Method for operating a light steering projection system and light steering projection system

Abstract

A method for operating a light steering projection system, comprising providing a light steering projection system comprising at least one laser, at least one phase modulator, at least one amplitude modulator, at least one projection lens, and a camera system, including a camera sensor; capturing a reference image using the camera system when the projection system operates in non-steered mode, in which the phase modulator applies a same phase to all pixels; capturing one or more test images using the camera system when the projection system operates in steered mode, in which the phase modulator generates varying illumination patterns by applying different phases to different pixels; comparing the test images to the reference image to determine relative changes in illumination; determining whether the relative changes exceed a predetermined threshold; and if the relative changes exceed the predetermined threshold, adjusting target brightness values of images to be displayed such that a radiance emitted by the projection system remains below a predetermined laser safety classification threshold corresponding to a predefined laser safety classification.

Description

[0001] METHOD FOR OPERATING A LIGHT STEERING PROJECTION SYSTEM AND LIGHT STEERING PROJECTION SYSTEM

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to projection systems, and more particularly to a method for operating a light steering projection system as well as to a light steering projection system employing such method.

[0004] TECHNICAL BACKGROUND

[0005] Movies and other visual content are often enjoyed by projecting images onto a screen for viewing. One factor that strongly affects the realism and impact of projected images is dynamic range - the difference between the highest and lowest light intensity in an image. There is increasing demand for high resolution, high dynamic range (HDR) projectors capable of projecting images with high intensity highlights. Such projectors can provide significantly enhanced viewing experiences.

[0006] Light steering is an emerging technology that may be used to realize HDR projectors. Light steering involves concentrating light that would otherwise be directed to darker areas of an image to provide bright image highlights. These highlights may have light intensities many times higher than the full frame uniform intensity achievable by the same projector. As such, light steering technology can help achieve both high dynamic range and high maximum intensity in highlights for a vivid viewing experience.

[0007] As the demand for more immersive and compelling viewing experiences increases, there is growing interest in projector technologies that can deliver higher light intensities. At the same time, ensuring user safety and regulatory compliance remains paramount. This creates engineering challenges in balancing performance capabilities with safety requirements in advanced projection systems. Projectors capable of very high light intensity output, whether achieved using light steering or other technologies, present potential safety concerns. There is a risk that a person's vision could be damaged if they look directly at the output of such a projector. To mitigate this risk, standards specify limits on the maximum radiant exposure that projectors can deliver at fixed distances from their output. Projector manufacturers must ensure their systems comply with these safety standards and regulations.

[0008] The laser safety standard IEC 60825-1 :2014 provides specific criteria for classifying laser products. For cinema projection systems, the goal is typically to achieve a classification of Class 1 Risk Group 3 (RG3) or lower. The standard specifies a formula in Clause 4.4 for determining the classification:

[0009] LT= (1 MW.m-2.sr1) / a

[0010] Where:

[0011] LT is the maximum radiance (or maximum radiant exposure) level emitted by the projector (or the projection system)’s light beam to be classified as a laser class 1 device. a is the angular subtense of the apparent source, determined at 200mm from the closest point of human access.

[0012] This formula establishes the relationship between various factors that determine the laser classification. For a light steering projector, the ability to create very bright highlights could potentially cause the system to exceed the limits for Class 1 RG3 and move into a higher, more restrictive classification such as Class 4. This would be undesirable for most cinema applications, as it may require additional safety measures and limit the usability of the projector in typical viewing environments. To partially solve this problem, various approaches have been proposed for monitoring and controlling light output in projection systems. US Patent 11,463,665 describes a closed loop driving system for a highlighter type projector that uses an image sensor to provide feedback for improving highlights projected by the projection system. The system captures images of the illumination pattern incident on an amplitude modulator and uses this feedback to adjust the driving of the projection system. However, this approach relies on absolute threshold comparisons which can be unreliable over time due to sensor degradation and optical component changes, making it insufficient for maintaining stable laser safety classification.

[0013] WO 2023 / 104787 attempts to address some of these limitations by introducing reference illumination to the sensor system to provide more absolute measurements. This approach includes a calibration light source that directs calibration light onto portions of a light sensor, allowing the system to determine irradiance levels based on the response to both the projected light and the calibration light. While this method removes some sensor degradation effects, it still suffers from degradation of other optical components in the system and cannot fully account for all factors that affect the actual light output from the projection lens.

[0014] Both approaches face fundamental challenges in providing reliable, long-term monitoring of laser safety classification limits. The degradation of optical components over time, variations in environmental conditions, and the complex relationship between measured sensor values and actual projected light intensity create uncertainties that can compromise compliance to a desired / predefined laser safety classification. Additionally, these systems do not adequately address the specific challenges posed by light steering technology, where the concentration of light into small highlights can dramatically affect the laser classification while being difficult to predict and control accurately.

[0015] DISCLOSURE OF THE INVENTION

[0016] The invention is based on the technical problem of ensuring that a light steering projection system maintains its intended laser safety classification while still leveraging the capabilities of light steering technology to enhance image quality and dynamic range. Existing monitoring approaches suffer from degradation effects and cannot reliably maintain laser classification limits over time, particularly when light steering concentrates light into high-intensity highlights that may exceed one or more predefined laser safety classification thresholds which correspond to predefined laser safety classifications.

[0017] The problem is solved by a method according to claim 1 respectively a system according to claim 11. Independent claims 21 and 22 relate to a controller respectively to a computer program product for implementing the inventive method. Advantageous embodiments are defined in the dependent claims, which provide enhanced functionality including temperature compensation, calibration processes, adjustable brightness values, adjustable power of any one or combination of the at least one laser, controllable function of any one or combination of the at least one phase modulators, and various camera system configurations for improved monitoring and control of the light steering projection system.

[0018] According to a first aspect of the present disclosure defined in claim 1, a method for operating a light steering projection system is provided. The method includes providing a light steering projection system comprising at least one laser, at least one phase modulator, at least one amplitude modulator, at least one projection lens, and a camera system. The phase modulator is a spatial light modulator having individually controllable pixels that can apply different phase values to incident light. In a non-steered mode, the phase modulator applies the same phase to all of its pixels, essentially functioning as a mirror with minimal diffraction losses. In a steered mode, the phase modulator generates varying illumination patterns by applying different phases to different pixels, thereby for instance concentrating light into specific areas to create bright highlights.

[0019] The method includes capturing a reference image using the camera system when the projection system operates in non-steered mode, establishing a baseline measurement. During steered mode operation, one or more test images are captured and compared to the reference image to determine relative changes in illumination. When these relative changes exceed a predetermined threshold, indicating that the light steering may cause the system to exceed its intended laser safety classification, the method adjusts target brightness values of images to be displayed such that a radiance emitted by the projection system remains below a predetermined laser safety classification threshold corresponding to a predefined laser safety classification. The radiance may be resulting from the projected image.

[0020] This approach differs fundamentally from prior art solutions by using relative measurements rather than absolute threshold comparisons. By comparing current illumination levels to a reference baseline captured by the same camera system, the method eliminates the reliability issues caused by sensor degradation and optical component changes over time. The reference baseline operation can be based on a lumen cap, which is a The system relies primarily on the linearity of the camera sensor, which can be assured through proper sensor selection, rather than attempting to maintain absolute calibration of the entire optical path. This relative measurement approach, combined with the lumen cap and dynamic brightness adjustment, provides a robust method for maintaining laser safety classification in light steering projection systems while preserving image quality and dynamic range capabilities.

[0021] As used herein, “radiance” refers to the optical power per unit area per unit solid angle emitted from the projector or projection system, typically measured in watts per square meter per steradian (W / m2sr). This parameter may directly relate to the potential exposure risk for human eyes and skin. The method may comprise monitoring of the radiance resulting from the projected image, including any increases due to light steering or other operational modes. When the measured radiance, as determined by the camera system, exceeds a predetermined threshold associated with the predefined laser classification, the projection system may automatically adjust the target brightness values of the images to be projected / displayed. This ensures that the projection system operates within the safety limits of the selected laser class, thereby maintaining compliance with applicable regulatory standards and preventing unintentional escalation to a higher, more restrictive classification.

[0022] The lumen cap may be implemented in various configurations depending on the specific application requirements and operational constraints. The lumen cap may be established or predetermined as a factory setting that provides a fixed maximum light output in non-steered operation mode, determined during manufacturing based on the projector's optical components and intended laser safety classification. Alternatively, the lumen cap may be configured as a fixed setting established at installation, allowing for customization based on the specific projection environment while maintaining stability throughout the system's operational life.

[0023] In embodiments, the predetermined lumen cap, which sets the maximum allowable light output of the projection system, is not chosen arbitrarily, but is calculated to ensure compliance with the selected laser safety classification (for example, Class 1 RG3). This calculation takes into account both the regulatory threshold for maximum permissible radiance and the expected relative change in illumination that may occur due to light steering.

[0024] In more advanced embodiments, the lumen cap or preferably the predetermined threshold may be implemented as an adjustable setting that can be modified over time. Such adjustable lumen caps or preferably the adjustable predetermined threshold may be automatically adjusted based on component degradation over time, ensuring that the system maintains its intended laser safety classification even as optical components age and their performance characteristics change. Temperature variations, which can affect laser output and optical component behavior, may also trigger automatic adjustments to the lumen cap to compensate for thermal effects on the system's light output. Additionally, system calibration results obtained (as will be outlined below) during periodic maintenance or recalibration procedures may provide data that necessitates lumen cap adjustments to maintain optimal performance while ensuring continued compliance with laser safety standards.

[0025] This flexibility in lumen cap or threshold configuration allows the light steering projection system to adapt to various operational scenarios while maintaining the fundamental laser safety classification constraint that prevents the system from exceeding its intended laser classification limits.

[0026] The predetermined threshold used to determine when brightness adjustments are necessary may be calculated based on laser safety classification requirements, such as for example the standards set forth in IEC 60825-1 :2014 for maintaining Class 1 RG3 classification or lower, particularly based on the predetermined laser safety classification threshold. This threshold represents the maximum allowable increase in brightness that can occur through light steering before the system risks exceeding its intended laser safety classification. The threshold calculation may take into account one or more factors such as the established or predetermined lumen cap, the projection distance, screen characteristics, and the specific wavelengths of the laser sources. By basing the threshold on established laser safety standards rather than arbitrary values, the system ensures compliance with regulatory requirements while maximizing the available dynamic range for image enhancement. The relationship between the lumen cap and the predetermined threshold creates a comprehensive safety framework that prevents the light steering capabilities from pushing the projection system into a higher, more restrictive laser classification category.

[0027] According to preferred embodiments, the camera system may utilize specific test patterns to enhance the accuracy and reliability of the relative change measurements. The reference image captured in non-steered mode may comprise a test pattern specifically designed for calibration and monitoring purposes. These test patterns provide known illumination characteristics that facilitate precise comparison with subsequent measurements. Similarly, the one or more test images captured in steered mode may comprise corresponding test patterns projected with light steering active, allowing for direct comparison of the same pattern under different operational conditions. The use of standardized test patterns eliminates variables introduced by content-dependent illumination variations and provides consistent reference points for measuring the effectiveness of light steering operations.

[0028] The camera system may operate in different modes depending on the specific monitoring requirements and operational constraints. In a real-time mode during projection, the camera continuously captures images and provides immediate feedback on light steering performance, enabling at least one of dynamic adjustment of brightness values, dynamic adjustment of power (or current) values to any one or combination of the at least one laser, and dynamic controlling of any one or combination of the at least one phase modulator, during content playback. This realtime monitoring ensures that any unexpected increases in light concentration are immediately detected and corrected. Alternatively, a start-up check mode may be employed where the camera performs a series of measurements using predetermined test patterns when the projection system is initialized, verifying that the light steering capabilities remain within acceptable limits before content projection begins. A periodic check mode at predetermined intervals provides ongoing verification of system performance without the computational overhead of continuous monitoring, striking a balance between laser safety classification assurance and system efficiency.

[0029] In one embodiment, temperature compensation may be applied to maintain stable laser output and ensure the lumen cap remains effective over varying environmental conditions. In this embodiment, the method includes monitoring the temperature of the laser components, as laser diode performance characteristics change significantly with temperature variations. Based on measured temperature variations, the output of the laser is automatically adjusted such that the output remains below a predetermined or established lumen cap, preventing thermal effects from causing unintended increases in light output that could compromise the laser safety classification. This temperature compensation ensures consistent performance across different operating environments and prevents thermal drift from affecting the precision of the light steering control system.

[0030] In a particularly preferred embodiment, the method includes a calibration process that establishes the operational parameters for the light steering projection system. While the core monitoring and adjustment functionality can operate with pre- established parameters, this calibration process provides optimal performance by tailoring the system behavior to the specific installation environment and projection conditions.

[0031] The calibration process may be performed at installation to initially configure the system for its intended operating environment, and may be repeated at predetermined intervals to account for component aging and environmental changes over time. During calibration, the system determines expected screen brightness based on the established lumen cap and relevant projection parameters such as screen size, projection distance, and optical component characteristics. The actual screen brightness is then measured in non-steered mode, providing a real-world baseline that accounts for factors such as screen gain, ambient conditions, and actual optical system performance.

[0032] By comparing the measured screen brightness to the expected screen brightness, the calibration process identifies any discrepancies between theoretical and actual system performance. Based on this relationship, derating information is determined that will be used during operation to ensure that brightness adjustments maintain the system within its intended laser safety classification. When the actual screen brightness is less than expected - indicating conditions such as an oversized screen, component degradation, or suboptimal installation parameters - the derating information provides the scaling factors needed to adjust target brightness values appropriately.

[0033] The derating information determined during this calibration process may be stored in a calibration file that contains all relevant information for generating highlights with correct brightness at desired locations. This calibration file serves as the reference data that guides the ongoing monitoring and adjustment process, ensuring that the light steering system operates safely while maximizing image quality within the constraints of the available light budget. The derating process may be implemented in different ways depending on the specific requirements and detected conditions. In a simple approach, when the actual screen brightness is half of the expected brightness (indicating, for example, an oversized screen), the entire brightness range may be scaled proportionally - for instance, a target range of 20 to 2000 nits may be scaled down to 10 to 1000 nits. However, in more sophisticated implementations, the derating may preserve the lower brightness levels while more aggressively reducing the peak brightness levels, such as scaling the same 20 to 2000 nit range to 14 to 1000 nits. This approach maintains better reproduction of darker content areas while ensuring that the highlight peaks remain within the laser safety classification limits. The specific derating strategy may be selected based on factors such as the degree of brightness discrepancy, the content type being projected, and the desired balance between laser safety classification compliance and image quality preservation.

[0034] Thus, the invention advantageously allows handling both simple proportional scaling and more nuanced approaches that better preserve image quality in the lower brightness ranges.

[0035] According to another aspect of the invention as defined in claim 11 , a light steering projection system is provided that implements the inventive method through integrated hardware and software components. The system comprises at least one laser as the primary light source, at least one phase modulator configured to operate in both non-steered and steered modes, at least one projection lens for directing light toward the projection screen, and a camera system configured to capture images for monitoring purposes. The projection system is typically configured for cinema projection applications, and will as such comprise a multitude of lasers of at least three different colors.

[0036] The phase modulator represents a key component that enables the light steering functionality by selectively applying phase modifications to different regions of the incident light beam. In the non-steered mode, the phase modulator applies a uniform phase to all of its pixels, effectively functioning as a reflective element that maintains the original light distribution. In the steered mode, the phase modulator generates varying illumination patterns by applying different phases to different pixels, thereby redirecting and concentrating light to create desired highlight effects. The camera system serves as the monitoring component that enables the relative measurement approach central to the invention. Unlike prior art systems that rely on absolute measurements prone to degradation effects, the camera system captures both reference images in non-steered mode and test images in steered mode, allowing for reliable relative comparisons that remain stable over time.

[0037] The controller represents the intelligence of the system, coordinating the operation of all components to maintain laser safety classification while optimizing image quality. The controller may be implemented as a single integrated unit or may comprise separate modules, processors, or computing elements that work together to perform the required functions. For example, the controller may include dedicated image processing modules for handling camera operations, separate control modules for laser output management, and central coordination modules for overall system control. The controller manages the capture timing of reference and test images, performs the critical comparison calculations to determine relative changes in illumination, evaluates whether these changes exceed the predetermined threshold, and implements the necessary brightness adjustments when required. This integrated approach ensures that all system components work together seamlessly to achieve the dual objectives of enhanced image quality through light steering and maintained compliance with laser safety standards, regardless of whether the controller functionality is centralized in a single unit or distributed across multiple interconnected modules.

[0038] Preferred embodiments of the light steering projection system provide enhanced functionality and operational flexibility. The controller may be further configured to execute any of the method steps described above, allowing the system to implement the full range of operational modes and adjustment strategies including the various test pattern approaches, operational modes, temperature compensation, and calibration processes. The system is specifically configured to maintain a laser classification of Class 1 RG3 or lower, while also maximizing the light steering capabilities available within those constraints.

[0039] The camera system may be implemented in various configurations depending on the specific installation requirements and operational constraints. In one embodiment, the camera system is integrated within a projector housing of the projection system, providing a compact and protected monitoring solution that eliminates external components and reduces installation complexity. This integrated approach also minimizes the risk of misalignment or interference from external factors. Alternatively, the camera system may be external to the projector housing and positioned to capture images from the projection system, allowing for flexible placement and potentially better access to the full projected image area. External camera systems may be particularly advantageous in installations where the projector housing space is limited or where direct observation of the screen image is preferred. In some implementations, the system may comprise multiple cameras placed at different locations to provide comprehensive monitoring coverage, redundant safety verification, or specialized monitoring of different aspects of the light steering performance.

[0040] In embodiments requiring enhanced thermal stability, the controller may be further configured to apply temperature compensation by adjusting output of the laser based on measured temperature variations. This temperature compensation capability is particularly valuable in environments with significant temperature fluctuations or in high-performance installations where maximum light output consistency is required. The temperature compensation algorithms may account for the specific thermal characteristics of the laser diodes used in the system, ensuring that thermal effects do not compromise either the light output stability or the laser safety classification.

[0041] The camera system may comprise an imaging sensor positioned to receive a portion of light from an optical path of the projection system, enabling direct monitoring of the light steering effects without requiring external image capture. This internal monitoring approach provides real-time feedback on the actual light distribution being generated by the phase modulator, allowing for precise control of the light steering intensity and pattern accuracy.

[0042] The system may further comprise at least one amplitude modulator configured to receive illumination patterns from the phase modulator, providing additional control over the final projected image characteristics. The amplitude modulator works in conjunction with the phase modulator to create the final image, with the phase modulator providing the light steering functionality and the amplitude modulator providing the content-specific intensity modulation. To ensure robust and safe operation, the controller may be configured to disable light steering if brightness increases continue to exceed the predetermined threshold after adjusting target brightness values. This fail-safe mechanism provides a final safety layer that prioritizes compliance with the intended laser safety classification over image enhancement capabilities, ensuring that the system cannot inadvertently exceed its intended classification even in fault conditions or unexpected operational scenarios.

[0043] The controller may be further configured to perform advanced operational functions that enhance both laser safety classification compliance and image quality optimization. In some embodiments, the controller determines a light budget based on the established lumen cap and measured screen brightness, representing the total amount of light available for content reproduction. This light budget encompasses both base light for general illumination and highlighter components for creating enhanced brightness features. The controller may then adjust the target brightness values based on the available light budget, ensuring that the system operates within its optical and safety constraints while maximizing the utilization of available light resources. When insufficient light budget is detected, the controller may implement appropriate scaling strategies to maintain image quality within the available constraints.

[0044] The controller may also be configured to generate and store calibration data containing the derating information for use during operation. This calibration data serves as a persistent reference that guides the ongoing brightness adjustment process, ensuring consistent performance across different operating sessions and environmental conditions. The stored calibration data may include relationships between measured and expected screen brightness, derating factors for different operational scenarios, and system-specific parameters that optimize the light steering performance for the particular installation.

[0045] In embodiments requiring robust feedback control, the controller may implement an iterative adjustment process, repeatedly adjusting the target brightness values and re-evaluating the relative changes until the relative changes fall below the predetermined threshold. This iterative approach provides enhanced safety assurance by ensuring that any adjustments successfully bring the system into compliance rather than simply applying a single correction that may prove insufficient.

[0046] According to further aspects of the invention, a controller for a light steering projection system is provided as defined in the independent claims. The controller comprises a processor and memory storing instructions that, when executed, implement the inventive method steps. This controller may be implemented as a standalone unit or integrated within the projection system, providing the computational intelligence necessary for the relative measurement approach and dynamic brightness adjustment capabilities.

[0047] Additionally, a computer program product is provided comprising instructions that, when executed by a processor, cause the processor to perform the inventive method. This computer program product enables the implementation of the inventive approach on various hardware platforms and allows for software updates and enhancements to the light steering control algorithms while maintaining the core safety and performance benefits of the relative measurement approach.

[0048] Further advantages and details of the invention will become apparent from the following detailed description of preferred embodiments in conjunction with the drawing, which comprises five figures.

[0049] BRIEF DESCRIPTION OF THE DRAWING

[0050] Fig. 1 illustrates a simplified optical setup demonstrating the problem addressed by the invention, showing how projection distance affects the light intensity required to achieve the same brightness on screens at different distances.

[0051] Fig. 2 illustrates a schematic layout of an optical system for a projector, according to aspects of the present disclosure.

[0052] Fig. 3 depicts a schematic layout of a light steering projector system with integrated image sensing, according to an embodiment. Fig. 4 shows a schematic diagram of an optical setup using a reference light source for testing a sensor.

[0053] Fig. 5 depicts a flow diagram of a projection system with light steering and feedback control, according to aspects of the present disclosure.

[0054] DESCRIPTION OF PREFERRED EMBODIMENTS

[0055] Fig. 1 illustrates a key problem addressed by the present invention. A light steering projection system 10 (also called projector for short), projects light within a certain projection cone schematically indicated by lines 12 and 14 representing upper and lower boundaries of such cone. Lines 16 and 18 schematically represent screens at different distances from the projector. Screen 16 is positioned at a distance of 1 unit from the projector, while screen 18 is at a distance of 2 units. To achieve the same perceived brightness on both screens, the projector 10 must output significantly more light to screen 18 than to screen 16. Specifically, assuming rectangular screens with the same aspect ratio, the area of screen 18 is 4 units (in this case units related to the area), while the area of screen 16 is 1 unit. This relationship follows from the inverse square law of light propagation, where doubling the projection distance results in four times the illuminated area for the same projection cone angle. This means that to maintain the same brightness on screen 18 as on screen 16, the projector must output 4 times as much light. This increased light output can potentially cause the projector to exceed its intended laser classification, which may be measured as schematically indicated by sensor 20, potentially moving from e.g. a Class 1 RG3 device to a more restrictive e.g. Class 4 classification.

[0056] The present invention addresses this challenge by using a camera system to monitor relative changes in illumination and adjusting target brightness values when necessary, ensuring that the projector maintains its intended laser classification while still providing optimal image quality across a range of projection scenarios. The monitoring may be performed continuously during operation, at system start-up, or at periodic intervals, depending on the specific implementation and operational requirements. The system employs a camera system to capture reference images in non-steered mode and test images during light steering operation, comparing these images to determine when brightness adjustments are required to stay within the intended laser classification limits.

[0057] In a preferred embodiment, a reference image using the camera system is captured when the phase modulator operates in non-steered mode, where it applies the same phase to all pixels. During light steering operation in steered mode, where the phase modulator applies different phases to different pixels to concentrate light into highlights, the camera captures test images. By comparing these test images to the reference image, the system determines relative changes in illumination, calculating a highlight factor (HLF) that indicates how much brighter the steered light has become compared to the baseline. When this relative change exceeds a predetermined threshold calculated based on laser safety classification requirements, the system automatically adjusts the target brightness values of the incoming video signal to maintain compliance with the predefined laser classification, for the projector having an established lumen cap. This relative measurement approach eliminates reliability issues caused by sensor degradation over time, relying primarily on the linearity of the camera sensor rather than absolute calibration of the entire optical path.

[0058] For example, when projecting to a nearby screen (like screen 16 in Fig. 1), the system operates within its established lumen cap with sufficient light budget available to achieve desired brightness levels without requiring derating. When projecting to a more distant screen (like screen 18), the system may need to apply derating to the target brightness values to ensure it can maintain its predefined laser classification. The calibration process measures the actual screen brightness compared to expected values, and when the actual brightness falls short due to factors such as increased projection distance or oversized screens, the system applies appropriate derating factors to scale the content brightness accordingly. This approach allows the projector to provide optimal image quality within the available light budget while ensuring safety and regulatory compliance. The system continuously monitors its light output using the camera system and adjusts as necessary to stay within the predetermined thresholds for its intended laser classification, preventing the transition from Class 1 RG3 to the more restrictive Class 4 classification that would significantly limit the projector's usability in typical cinema environments. Referring to Fig. 2, an exemplary layout of a light steering projection system 10 is illustrated. Within a projector housing 22, system 10 includes at least one laser 24, at least one phase modulator 26, at least one amplitude modulator 28, and at least one projection lens 30. In some aspects, the system may also include other optical components such as lenses 32, mirrors 34, and other optical components such as, but not limited to, filters, polarizers, rods, and diffusers, which can be used to relay the light from one point to another.

[0059] The phase modulator 26 is configured to generate, from light provided by the at least one laser 24, an illumination pattern or highlight image, which is incident on the amplitude modulator 28 and then projected via projection lens 30. In some cases, if the phase modulator 26 is configured to apply the same phase to all pixels, it essentially works as a mirror with some minor diffraction losses. This configuration is referred to as a non-steered mode.

[0060] The amount of light that can be steered by the phase modulator 26 is referred to as the steerable light. This steerable light is an important part of the light budget, which determines how many highlights of certain brightness can be maximally made with a given system. In some cases, if there are multiple phase modulators, the light budget can be denoted as being the sum of the steerable light of the separate modulators. If there is a non-steerable component present, it also contributes, or sums, to the final light budget.

[0061] Such a non-steerable component can be a phase modulator being configured in non-steered mode. It can also be a portion of light which does not interact with the phase modulator but goes straight to the amplitude modulator.

[0062] In some embodiments, the light steering projection system also includes a camera system, of which in the schematic drawings only camera sensor 36 is shown. The camera system can measure relative changes in brightness when the projector is steering light. This provides information on how strong light is being steered and hence on how many times brighter the final brightness is getting. Because of the relative way of measuring, the impact of components degrading over time is eliminated. The system only relies on the linearity of the sensor, which can be assured by using a respective high-quality sensor. In the embodiments shown in Figures 2, 3 and 4, the camera system can be made as an internal component of the projector. In these embodiment the camera system is constructed to capture a small portion of the light in the projector. This light is split from the main optical path, which can be done in multiple ways. As shown in Fig. 2, this can be done by putting a partially transparent glass plate 38 in the optical path, and putting the camera sensor 36 and optics in the reflection path. As shown in Fig. 3, this can be done by putting the camera sensor 36, and other optics like lenses 32, behind a partially transparent mirror 40. As shown in Fig. 4, which shows the part of a projector indicated by the dashed-dotted line VI in Fig. 2 (but differently configured), where the camera sensor 36 and lenses 32 are behind a partially transparent mirror 40, onto which also light from a reference brightness source 42 can also be shown to test / calibrate the camera sensor 36. As in Fig. 2, a small portion of the light from the phase modulator is split from the main optical path by putting a partially transparent glass plate 38 in the optical path. The reference brightness source 42 can be used to enhance the quality of the captured image, particularly in low-light conditions or when the projected light is of low intensity. The reference brightness source 42 can be provided by a separate light source, such as a LED or another laser, and can be directed towards the camera sensor 36 using a partially transparent mirror 40 or other optical components.

[0063] The camera system can also be made as an external component of the projector. In such embodiment, the camera is constructed to capture the image that arrives on the projection screen. Again, there are several ways to realize this. The camera can be made as a fixed part of the projector (e.g. mounted fixed above the projection lens).

[0064] Alternatively, the camera can be made as a separate component that connects to the projector via wire or wireless. In this case, the camera can then be mounted on a location where it can fully capture the projection screen.

[0065] Special routines in the algorithms need to be added to remove all the external influences on the camera (e.g. room lights, obstructions, etc.).

[0066] When used in real time mode, the camera requires a fast sensor and / or good subsampling. Subsampling introduces uncertainty because a large part of the information is not captured, so there is a risk of missing the actual maximum in the signal. It also requires a good flat fielding of the camera to compensate for any roll- off introduced by the optical path. The camera must also capture a high quality, representative image that has the same characteristics as the final on screen image, for any possible shape or brightness of the image.

[0067] The camera can be used in a “start-up check” mode. This can use a set of test patterns. This reduces the need for high quality, representative, images to only those specific patterns. Furthermore, it can use a set of test patterns which are characterized individually. For each of those patterns a set of coefficients is used to relate the camera capture to the on screen brightness. The parameters can be fixed from factory and can be adjustable to accommodate component swaps during the lifetime of the product. Strict procedures apply when changing any of these parameters.

[0068] The camera can be monochrome. Performing a classification check with a monochromatic camera requires the check to be performed RGB sequential. Laser sources need to be switched to get only one color onto the camera. Or light from the other colors needs to be steered off-screen, this means it also does not reach the camera. This method is a bit less accurate due to some stray light always getting through.

[0069] The camera can be RGB. Performing the classification check with a color camera means that the check can be performed with a single capture. A color camera has cross talk between pixels of different colors. The camera or the processing algorithm thus needs a color decomposition matrix. The matrix can be factory installed. Because we use laser wavelengths, we can assume that most projectors have spectra which are sufficiently similar to each other. A factory calibrated camera would thus respond similar in all projectors. The matrix can be computed in the projector itself. Because we will eventually use the camera for relative measurements it is possible to show, mathematically, that the matrix can differ up to a scale factor per color. By registering a certain list of patterns such a matrix can be constructed.

[0070] The camera can be used in a feedback system. If the camera detects a brightness increase which is too large, the content can be derated. After the content is derated a new check is performed until it passes. If the loop keeps going, at some point light steering is disabled. The camera can be made with buffers to account for various factors, including measurement errors, the impact of component swaps during the lifetime of the product, variance in projection lens throughput, and variance in laser wavelengths. Changes in laser wavelength(s) may cause the lumens per Watt ratio in the light beams to change, meaning that for the same lumen output the radiance may become higher. Since the laser safety classification is based on radiance, such variations can be critical if they shift in an unfavorable direction.

[0071] Fig. 5 depicts a flow diagram of a projection system with light steering and feedback control, according to aspects of the present disclosure. The process begins with the establishment of a lumen cap 44, which sets the maximum allowable light output in non-steered mode and serves as the foundation for the system's laser safety classification compliance.

[0072] The calibration process 50 receives inputs including the lumen cap 44, actual measured screen brightness 46 ("Nits on screen"), and expected screen brightness 48 ("Expected Nits on screen"). The calibration 50 compares these values to determine the relationship between the available light budget and the projection requirements. When the actual measured screen brightness 46 is less than the expected screen brightness 48, this indicates conditions such as an oversized screen or increased projection distance that may require content adjustment to maintain laser classification compliance.

[0073] The video signal processing begins with a video signal input 52, which undergoes signal capping 54 based on parameters determined by the calibration 50. This produces a capped video signal 56 that is fed into the light steering algorithm 58. The calibration 50 provides derating information to both the algorithm 58 and the signal capping 54 process, ensuring that the content brightness remains within the available light budget.

[0074] The algorithm 58 output controls the light steering 60 operation, which concentrates light to create highlights in the projected image. A camera 62 monitors the light steering 60 output and measures the highlight factor (HLF) - the ratio of steered to non-steered brightness. If the camera 62 detects that the HLF exceeds the predetermined threshold, it provides feedback to the signal capping 54 process to further reduce the content brightness. This feedback loop ensures that even if the initial calibration-based derating is insufficient, the system can dynamically adjust to maintain laser classification compliance.

[0075] Finally, the processed and controlled light beam representing an image with a certain brightness profile is projected onto the screen 64. This integrated approach combines calibration-based derating with real-time camera monitoring to ensure that the system maintains its intended laser classification while maximizing image quality within the available light budget.

[0076] The calibration process 50 accounts for various installation factors that affect the light budget. The actual measured screen brightness 46 reflects real-world conditions including screen size, projection distance, screen gain, and optical system performance. When this measured value falls short of the expected screen brightness 48, the calibration 50 determines appropriate derating factors to scale the content brightness accordingly, ensuring that the highlight generation remains within the laser classification limits, for the projector which is subject to an established lumen cap 44.

[0077] The highlight factor (HLF) is calculated as a ratio of the measured brightness in a steered light condition to the brightness in a non-steered condition. The camera system captures a reference image in the non-steered mode and stores it in memory. When the projection system operates in light steering mode, the camera system captures subsequent images and compares them to the stored reference image to determine the HLF. The highlight factor can be evaluated and determined at a location inside of the projector before the light is modulated by an amplitude modulator (28) or on the projection screen (64), with the amplitude modulator (28) in that case set to maximum throughput for all pixels, so that the illumination profile of the amplitude modulator is projected in an unmodified way on that projection screen.

[0078] The HLF calculation may involve pixel-by-pixel comparison between the reference image and the current image. In some cases, the system may calculate an average HLF across the entire image, while in other cases, it may calculate separate HLFs for different regions of the image. The system may use various statistical methods, such as mean, median, or maximum values, to determine the representative HLF for the image or region. In some implementations, the system may apply weighting factors to different regions of the image when calculating the HLF. For example, central regions of the image may be given higher weight than peripheral regions, as they may be more critical for maintaining the desired laser classification. This regional weighting approach allows the system to prioritize the most visually important areas while ensuring overall compliance with safety standards.

[0079] The calculated HLF is compared to a predetermined threshold value set based on the desired laser classification and relevant safety standards such as I EC 60825- 1:2014. If the HLF exceeds this threshold, the system initiates the derating process for the incoming video signal. The derating process involves scaling down the brightness of the video signal by a factor related to the extent by which the HLF exceeds the threshold.

[0080] The system may employ hysteresis in the decision-making process for derating. For example, once derating is initiated, the system may require the HLF to fall below a lower threshold before ceasing the derating process. This approach helps prevent rapid oscillations between normal operation and derating, ensuring stable system behavior. In some aspects, the system may implement a gradual derating process, where the derating factor is increased incrementally over time if the HLF remains above the threshold, minimizing sudden changes in image brightness that could be noticeable to viewers.

[0081] The calibration process generates a file containing information needed to produce highlights with correct brightness at desired locations. This calibration is performed at the installation location and registers the behavior of the light steering for that particular projector. The calibration file includes the desired nits on screen in nonsteered mode (a pre-filled value that remains consistent) and the actual measured nits on screen as determined during installation.

[0082] The ratio between the measured and expected nits is crucial for determining system behavior. When the actual screen brightness is less than expected (Yscreen < Yref), this indicates conditions such as an oversized screen or insufficient light budget, potentially requiring content derating to maintain the desired laser classification. This ratio also indicates whether sufficient light is available to correctly reproduce content on the screen. The highlight factor represents the amount of highlighting needed to achieve a given on-screen brightness. If the on-screen nits are lower than expected, the highlighter must work harder to reach the target, thereby increasing the HLF. For example, if the expected nits are 30 and the target nits are 300, a correct installation would yield an HLF of 10 (300 / 30). However, for an oversized screen where the actual screen nits drop to 15, the HLF would increase to 20 (300 / 15), potentially exceeding the threshold for the intended laser classification.

[0083] Derating is based on the ratio between the expected nits and the actual screen nits. If the ratio of screen nits to expected nits is 0.5, the system may derate the target brightness by a factor of 0.5. This scaling ensures that the HLF remains within acceptable limits while addressing image quality concerns. The derating process can be triggered either by the calibration-based comparison of screen brightness values or by the camera system detecting excessive HLF values during operation.

[0084] The system employs the concept of a light budget, which represents the total amount of light available to produce content. This budget is divided into base light and highlighter components. The base light provides uniform illumination across the screen, typically targeting 44 nits, while the highlighter component can be redistributed to create bright features. If the base light budget is incorrect - for example, providing only 22 nits instead of the expected 44 - content in the range between 22 and 44 nits must be produced using the highlighter bucket, which was intended for creating highlights above 44 nits. This situation represents a "not enough light budget" condition that can compromise image quality.

[0085] Screen characteristics significantly impact system performance and laser safety classification. Screen gain affects how much light is reflected back to viewers, with higher gain screens allowing for larger screen sizes without violating classification limits. The formulas used to determine expected nits on screen take screen gains into account, enabling more accurate calibration and derating calculations.

[0086] The system employs temperature compensation by continuously monitoring the temperature of the laser components. Temperature variations affect laser diode performance, including optical power output and wavelength shifts. Based on the monitored temperature, the system determines changes in the laser's optical power and wavelength characteristics. The system then adjusts the current supplied to the laser to maintain color balance and control the optical power output, ensuring that the system remains compliant with the predetermined lumen cap in both nonsteered and steered modes.

[0087] The lumen cap is typically established as a factory setting that provides a fixed maximum light output in non-steered mode. This cap serves as a baseline for calculating allowable brightness increases during light steering operations. For a given throw ratio with laser power set at the lumen cap, the system can only reach desired maximum brightness levels up to a certain screen size. Beyond this size, brightness begins to drop because no additional light can be added due to the lumen cap constraint.

[0088] If the camera applies derating multiple times and the HLF remains too high, light steering may be disabled, which may also enable informing the user that the system is maybe working in a fault condition mode where light steering is not operating predictably. The system may then provide several recovery options: rebooting the system to reset the electronics and retry the HLF measurement, recalibrating the system to update the calibration file and recalculate all derating factors, or manually triggering the camera to check the HLF. The system may implement a process for gradually re-enabling light steering capabilities while continuously monitoring the HLF to ensure stable operation within the limits of the intended laser classification of the projector.

[0089] The system logs these events and adjustments to assist in long-term performance optimization and troubleshooting. This logging capability enables analysis of system behavior over time and helps identify patterns that may indicate component degradation or other issues requiring maintenance attention.

[0090] ADDITIONAL TECHNICAL CONSIDERATIONS

[0091] The system may comprise multiple cameras placed at different locations to provide comprehensive monitoring coverage, redundant safety verification, or specialized monitoring of different aspects of the light steering performance. This multi-camera approach enhances the reliability of the relative measurement system and provides backup monitoring capabilities. Screen gain characteristics play a significant role in system calibration and laser safety classification. Higher gain screens reflect more light back to viewers, potentially allowing for larger screen sizes without violating Class 1 RG3 classification limits as specified in IEC 60825-1:2014. The calibration process accounts for screen gain when determining expected screen brightness values and calculating appropriate derating factors.

[0092] The system may utilize specific test patterns during calibration and monitoring operations. These test patterns provide known illumination characteristics that facilitate precise comparison between steered and non-steered modes. Each test pattern may be individually characterized with coefficients that relate camera measurements to actual on-screen brightness, enabling more accurate HLF calculations.

[0093] For RGB camera implementations, the system may employ color decomposition matrices to account for cross-talk between pixels of different colors. These matrices may be factory-installed based on laser wavelength characteristics or computed within the projector itself using predetermined pattern sequences.

[0094] The iterative feedback process may continue adjusting target brightness values and re-evaluating relative changes until the HLF falls below the predetermined threshold. If this iterative process fails to achieve compliance after multiple attempts, the system implements the fail-safe mechanism of disabling light steering entirely.

[0095] The camera system may incorporate buffers to account for measurement errors, component variance during the product lifetime, and variations in laser wavelengths that affect the lumens-per-watt ratio. These buffers ensure robust operation even when component characteristics drift over time.

Claims

- 25 -CLAIMS1. A method for operating a light steering projection system comprising at least one laser, at least one phase modulator, at least one projection lens, and a camera system; the projection system adapted to project an image on a screen and to operate in: a non-steered mode, in which the phase modulator applies a same phase to all of its pixels; and a steered mode, in which the phase modulator generates varying illumination patterns by applying different phases to different of its pixels; the method comprising: capturing a reference image using the camera system in non-steered mode; capturing one or more test images using the camera system in steered mode; comparing the test images to the reference image to determine relative changes in illumination; determining whether the relative changes exceed a predetermined threshold; if the relative changes exceed the predetermined threshold, adjusting target brightness values of images to be displayed such that a radiance emitted by the projection system remains below a predetermined laser safety classification threshold corresponding to a predefined laser safety classification .

2. The method of claim 1, wherein the reference image comprises a test pattern projected in non-steered mode.

3. The method of claim 1 or 2, wherein the one or more test images comprise test patterns projected in steered mode.

4. The method of any of claims 1 to 3, wherein capturing the one or more test images is performed in at least one of: a real-time mode during projection; a start-up check mode; and a periodic check mode at predetermined intervals.

5. The method of any of claims 1 to 4, further comprising applying temperature compensation by: monitoring temperature of the at least one laser;adjusting output of the at least one laser based on measured temperature variations such that the output remains below a predetermined lumen cap.

6. The method of any of claims 1 to 5, further comprising a calibration process performed at least one of at installation or at predetermined intervals, the calibration process comprising: determining expected screen brightness based on the predetermined lumen cap and projection parameters; measuring actual screen brightness in non-steered mode; comparing the measured screen brightness to the expected screen brightness; and determining derating information based on a relationship between the expected screen brightness and the actual screen brightness.

7. The method of claim 6, wherein adjusting the target brightness values comprises applying the derating information when the actual screen brightness is less than the expected screen brightness.

8. The method of any of claim 6 or claim 7, wherein the predetermined lumen cap is one of: a factory setting; a fixed setting established at installation; or an adjustable setting.

9. The method according to claim 8, wherein the predetermined lumen cap is calculated based on the predetermined laser safety classification threshold and an expected relative change in illumination.

10. The method of any of claims 6 to 9, wherein the predetermined threshold is calculated based on the predetermined laser safety classification threshold and the predetermined lumen cap.

11. A light steering projection system comprising: at least one laser;at least one phase modulator configured to apply a same phase to all of its pixels in a non-steered mode and to generate varying illumination patterns by applying different phases to different of its pixels in a steered mode; at least one projection lens; a camera system configured to capture images; and a controller configured to: control the camera system to capture a reference image in nonsteered mode; control the camera system to capture one or more test images in steered mode; compare the test images to the reference image to determine relative changes in illumination; determine whether the relative changes exceed a predetermined threshold; and if the relative changes exceed the predetermined threshold, adjust target brightness values of images to be displayed such that a radiance emitted by the projection system remains below a predetermined laser safety classification threshold corresponding to a predefined laser safety classification.

12. The system of claim 11 , wherein the camera system is integrated within a projector housing of the projection system.

13. The system of claim 11 , wherein the camera system is external to a projector housing and positioned to capture images from the projection system.

14. The system of any of claims 11 to 13, wherein the controller is further configured to apply temperature compensation by adjusting output of the at least one laser based on measured temperature variations.

15. The system of any of claims 11 to 14, wherein the controller is further configured to execute the method of any of claims 1 to 10.

16. The system of any of claims 11 to 15, wherein the camera system comprises an imaging sensor positioned to receive a portion of light from an optical path of the projection system.- 28 -17. The system of any of claims 11 to 16, wherein the controller is configured to maintain a laser classification of Class 1 RG3 or lower.

18. The system of any of claims 11 to 17, further comprising at least one amplitude modulator configured to receive illumination patterns from the phase modulator.

19. The system of any of claims 11 to 18, wherein the controller is configured to disable light steering if brightness increases continue to exceed the predetermined threshold after adjusting target brightness values.

20. The system of any of claims 11 to 19, wherein the controller is further configured to perform at least one of: determining a light budget based on the lumen cap and measured screen brightness, and adjusting the target brightness values based on the available light budget; generating and storing calibration data containing the derating information for use during operation; and iteratively adjusting the target brightness values and re-evaluating the relative changes until the relative changes fall below the predetermined threshold.

21. A controller for a light steering projection system, comprising: a processor; and a memory storing instructions that, when executed by the processor, cause the controller to perform the method of any of claims 1 to 10.

22. A computer program product comprising instructions that, when executed by a processor, cause the processor to perform the method of any of claims 1 to 10.

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