Projection display apparatus and projection display method

Abstract

A projection display apparatus (50) irradiates an image modulation device with a luminous flux from a light source, and enlarges and projects an image formed on the image modulation device by using a projection lens. The projection display apparatus comprises: a detection unit (51) that detects the focal length of the projection lens; and a video processing unit (52) that sets the maximum display gradation of a display in the image modulation device to a reference value when the detected focal length is shorter than a threshold value, and sets the maximum display gradation of the display in the image modulation device to a limit value smaller than the reference value when the detected focal length is longer than the threshold value.

Description

Projection-type display device and projection-type display method

[0001] The present invention relates to a projection-type display device and a projection-type display method.

[0002] Projection-type display devices such as projectors are classified into risk groups according to the photobiological safety requirements of the IEC 62471-5 standard. Risk groups are classified into 0, 1, 2, and 3. Projection-type display devices in risk group 2 or lower can be used by general consumers without any particular restrictions. On the other hand, projection-type display devices in risk group 3 must be installed by a professional installer. In the case of projection-type display devices that use interchangeable projection lenses, the risk group is determined separately for the projection-type display device and the interchangeable projection lens. If the projection-type display device is in risk group 2, depending on the interchangeable projection lens, it may be divided into risk group 2 or lower and risk group 3, or all interchangeable projection lenses may be in risk group 2 or lower. In this case, when installing using an interchangeable projection lens in risk group 3, or when replacing it with an interchangeable projection lens in risk group 3, installation by a professional installer is required. If a projection-type display device is in risk group 3, installation and replacement of projection lenses must be carried out by the installer, regardless of whether interchangeable projection lenses are used. When using a projection-type display device in risk group 3, or a projection-type display device in risk group 2 or lower that uses interchangeable projection lenses in risk group 3, it is necessary to set up a no-entry zone to prevent dangerous projected light from entering people's eyes. In other words, there are restrictions on the use of projection-type display devices in risk group 3.

[0003] Furthermore, projection display devices with laser light sources are further classified into laser classes according to the IEC 60825-1 standard. Projection display devices that project visible light are classified into laser classes 1, 2, 3R, 3B, and 4, but laser classes 3B and 4 are restricted from being sold to general consumers.

[0004] However, an exception is provided in IEC 60825-1 (3rd edition), and if the projection display device meets specific conditions, it is evaluated by ICE 62471-5. The projection display device is classified as laser class 1 when it meets the specific conditions and laser class 4 when it does not meet the specific conditions. A projection display device of laser class 4 cannot be sold to the general public either.

[0005] Such various restrictions according to the IEC standards are caused by the increase in the brightness of the visible light projected by the projection display device. Also, even with the same brightness, various restrictions occur when the projection ratio of the projection lens becomes longer. Hereinafter, a risk group or laser class that can be sold to the general public without various restrictions is referred to as a "safety class".

[0006] As a method for avoiding such various restrictions, Patent Document 1 discloses a technique for controlling the output of a laser light source so that it does not exceed the exposure radiation limit value (AEL value) for satisfying the safety class of the projection display device in accordance with the change in the focal length (projection ratio) of a projection lens having a zoom function (hereinafter sometimes referred to as a "zoom lens").

[0007] However, in the technique disclosed in Patent Document 1, since the change in the light source output is performed stepwise in accordance with the focal length of the zoom lens, the output of the light source must always be changed first and then the focal length must be changed, resulting in complicated control.

[0008] International Publication No. 2010 / 109621

[0009] The problem to be solved is that in a projection display device with higher brightness, the control for maintaining safety regarding brightness is complicated over the entire range of the focal length of the projection lens.

[0010] One aspect of the present invention is a projection-type display device that irradiates an image modulation device with a light beam from a light source and magnifies and projects a display image formed on the image modulation device using a projection lens, comprising: a detection unit for detecting the focal length of the projection lens; and an image processing unit that, when the detected focal length is shorter than a threshold, sets the maximum display gradation of the display on the image modulation device to a reference value, and when the detected focal length is longer than the threshold, sets the maximum display gradation of the display on the image modulation device to a limit value smaller than the reference value.

[0011] Furthermore, one aspect of the present invention is a projection-type display method in a projection-type display device that irradiates an image modulation device with a light beam from a light source and magnifies and projects a display image formed on the image modulation device using a projection lens, wherein the focal length of the projection lens is detected, and if the detected focal length is shorter than a threshold, the maximum display gradation of the display on the image modulation device is set to a reference value, and if the detected focal length is longer than the threshold, the maximum display gradation of the display on the image modulation device is set to a limit value smaller than the reference value.

[0012] According to the present invention, in a projection-type display device with higher brightness, it is possible to easily control brightness safety across the entire focal length range of the projection lens.

[0013] This is a schematic block diagram showing the configuration of a projection display device according to the first embodiment of the present invention. This is a graph for illustrating a comparative example. This is a graph for illustrating the display control processing performed by the projection display device according to the first embodiment. This is a flowchart showing an example of the flow of display control processing performed by the projection display device according to the first embodiment. This is a graph for illustrating the display control processing performed by the projection display device according to the second embodiment of the present invention. This is a graph for illustrating an example of the image quality mode in the initial state of the projection display device according to the second embodiment. This is a graph for illustrating another example of the image quality mode in the initial state of the projection display device according to the second embodiment. This is a flowchart showing an example of the flow of display control processing performed by the projection display device according to the second embodiment. This is a graph for illustrating the display control processing performed by the projection display device according to the third embodiment of the present invention. This is a graph for illustrating the display control processing performed by the projection display device according to the fourth embodiment of the present invention. This is a block diagram showing the minimum configuration of a projection display device according to an embodiment of the present invention.

[0014] Hereinafter, a projection-type display device and a projection-type display method according to one embodiment of the present invention will be described with reference to the drawings.

[0015] [First Embodiment] First, a projection-type display device and projection-type display method according to the first embodiment of the present invention will be described.

[0016] Figure 1 is a schematic block diagram showing the configuration of the projection-type display device 1 according to the first embodiment. The projection-type display device 1 is, for example, a projector. The projection-type display device 1 connects to an external device by wire or wireless connection and generates a display image H based on the video signal received from the external device. The projection-type display device 1 then projects the generated display image H as a projected image G onto a projection surface such as a screen S. The projection-type display device 1 is a projection-type display device equipped with a projection lens 104 (zoom lens) having a zoom function, or a projection-type display device used by attaching an interchangeable projection lens (interchangeable projection lens) having a zoom lens.

[0017] The projection display device 1 comprises a light source unit 101, an illumination optical system 102, an image modulation device 103, a projection lens 104, a detection unit 105, an image processing unit 106, a light source drive control unit 107, and a lens recognition unit 108. The projection display device 1 irradiates the image modulation device 103 with a light beam from the light source unit 101, and projects the display image H formed on the image modulation device 103 as a projected image G using the projection lens 104.

[0018] The light source unit 101 is a laser light source such as a semiconductor laser or a solid-state laser. The light source unit 101 includes a phosphor and a laser for exciting the phosphor. The light source unit 101 may also have a laser for illumination light. Alternatively, the light source unit 101 may consist only of a laser. Furthermore, the light source unit 101 is not limited to a laser light source, but may also be a mercury lamp, a light-emitting diode, etc. The light source unit 101 irradiates the illumination optical system 102 with its illumination light.

[0019] The illumination optical system 102 is a lens system for uniformly illuminating the image modulation device 103 with light emitted from the light source unit 101 in proportion to its size.

[0020] The image modulation device 103 is a microdisplay that generates the display image. For example, the image modulation device 103 may be a transmissive liquid crystal light bulb, a DMD (Digital Micromirror Device), or an LCOS (Reflective Liquid Crystal System). The image modulation device 103 is illuminated by a light beam from the light source unit 101.

[0021] The projection lens 104 is a fixed or interchangeable zoom lens. The projection lens 104 may be an electric or manual lens. The projection lens 104 magnifies and projects the display image generated by the image modulation device 103 onto the projection surface. The projection lens 104 has a changeable focal length. The projection display device 1 can be fitted with multiple projection lenses 104 of different types. In other words, the projection display device 1 is an interchangeable zoom lens (projection lens 104). Each projection lens 104 has a lens ID to identify its type.

[0022] The detection unit 105 detects the zoom position corresponding to a change in the focal length of the projection lens 104, i.e., a change in the zoom magnification. The zoom position here refers to the position of a part of the internal lens group that constitutes the projection lens 104 when the focal length of the projection lens 104 (projection distance to the screen S or zoom magnification) is determined by moving a part of the internal lens group along the optical axis. For example, the detection unit 105 detects the zoom position by detecting the value of a potentiometer built into the projection lens 104. Note that the detection unit 105 may detect the zoom position by other methods, such as an encoder, rather than being limited to a potentiometer.

[0023] The video processing unit 106 performs image quality adjustment and resolution conversion on the video signal input to the projection display device 1, and outputs the converted video signal to the image modulation device 103. At this time, the video processing unit 106 determines the maximum drive current (i.e., maximum display gradation) of the image modulation device 103 based on the zoom position detected by the detection unit 105 and the type of projection lens 104 recognized by the lens recognition unit 108. The maximum display gradation is the maximum gradation in the display of the image modulation device 103. Then, the video processing unit 106 controls the image modulation device 103 with the determined maximum drive current. For example, the video processing unit 106 switches the image quality mode of the projection display device 1. The image quality modes will be described later. The video processing unit 106 includes a CPU (Central Processing Unit), memory, and a circuit for driving the image modulation device 103 (such as an LCD (Liquid Crystal Display) drive circuit or a DMD drive circuit). Each part of the video processing unit 106 may be a separate component or an integrated component.

[0024] The light source drive control unit 107 is responsible for supplying power to drive the light source unit 101 and controls the amount of power supplied to the light source unit 101 based on the detection result of the detection unit 105. The light source drive control unit 107 is composed of a CPU, memory, and a circuit for driving the light source unit 101 (such as a lamp drive circuit, LED drive circuit, or laser drive circuit). Each part of the light source drive control unit 107 may be a separate component or an integrated component.

[0025] The lens recognition unit 108 recognizes the type of projection lens 104 attached to the projection display device 1. For example, the lens recognition unit 108 recognizes the type of projection lens 104 by reading the lens ID from the projection lens 104 attached to the projection display device 1.

[0026] Next, as a comparative example to the display control processing of the projection-type display device 1 according to this embodiment, display control processing in related technologies will be described.

[0027] Figure 2 is a graph illustrating a comparative example. In graph G0 shown in this figure, the vertical axis represents the light source luminous flux (light source output (unit: W (watts)) or laser drive current), and the horizontal axis represents the projection ratio (throw ratio) of the projection lens 104. Since the projection ratio decreases as the focal length of the projection lens decreases, in this embodiment the focal length of the projection lens is expressed in terms of the projection ratio. The dotted line L1 shown in graph G0 indicates the boundary line between risk group 2 (hereinafter referred to as "RG2") and risk group 3 (hereinafter referred to as "RG3") in the ICE62471-5 standard. At each projection ratio, the light source output below this dotted line L1 is RG2, and the light source output above this dotted line L1 is RG3. In other words, this dotted line L1 indicates the standard boundary.

[0028] The solid line L2 shown in Graph G0 illustrates an example of controlling the light source output in a projection-type display device according to a comparative example. In the illustrated example, when the projection ratio exceeds 3.5, the value of the dotted line L1 becomes smaller than the maximum output of the light source, which is 100W. Therefore, the projection-type display device according to the comparative example drives the light source at its maximum output of 100W when the projection ratio is 3.5 or less, and controls the light source output so as not to exceed the standard boundary (dotted line L0) when the projection ratio exceeds 3.5.

[0029] However, this type of control has the problem of being complex because, in order to change the light source output in stages according to the focal length of the projection lens, the light source output must be changed first, and then the focal length must be changed.

[0030] Next, an overview of the display control processing in the projection-type display device 1 according to this embodiment, which solves these problems, will be described. Displays including the projection-type display device 1 usually have multiple image quality modes, and the chromaticity of white, red, green, and blue is changed depending on the image quality to change the color tone and color gamut of the displayed image. In particular, the projection-type display device 1 has an image quality mode that prioritizes brightness and an image quality mode that matches multiple color standards. Compared to the image quality mode that prioritizes brightness, the other image quality modes are generally dimmer. Here, the image quality mode that prioritizes brightness is defined as "Image Quality Mode 1 (First Image Quality Mode)," and "Image Quality Mode 2 (Second Image Quality Mode)" is defined as having 80% of the brightness of "Image Quality Mode 1" and matching the color standard. In "Image Quality Mode 1," the projection-type display device 1 can display at the maximum gradation of the image modulation device 103 (corresponding to the "reference value") when displaying "all white." On the other hand, in "Image Quality Mode 2," the projection display device 1 can only display up to 80% of the maximum gradation (corresponding to a "limit value smaller than the reference value") when displaying "all white."

[0031] In this embodiment, the maximum display gradation (reference value) in "Image Quality Mode 1" is set to the maximum gradation of the image modulation device 103, and the maximum display gradation (limit value) in "Image Quality Mode 2" is set to 80% of the maximum gradation. However, the limit value can be set to 90% of the maximum gradation, 70% of the reference value, or any other value where the limit value is classified as RG2 across the entire focal length range of the projection lens 104. In other words, the limit value is a value that does not exceed the standard boundary between RG2 and RG3 across the entire focal length range of the projection lens 104. That is, the limit value is a display gradation that satisfies the standard (safety standard) for the projected light from the projection display device 1 to be classified as RG2 across the entire focal length range of the projection lens 104.

[0032] Figure 3 is a graph illustrating the display control processing performed by the projection-type display device 1 according to the first embodiment. In graph G1 shown in this figure, the vertical axis represents the maximum display gradation level of the image modulation device 103 (unit: % (percent)), and the horizontal axis represents the projection ratio (Throw Ratio; Throw Ratio) of the projection lens 104. The maximum display gradation level is the maximum display gradation level of the display in the image modulation device 103 (percentage of the maximum gradation). The dotted line L11 shown in graph G1 indicates the boundary line between RG2 and RG3. For each projection ratio, the maximum display gradation level below this dotted line L11 is RG2, and the maximum display gradation level above this dotted line L11 is RG3. In other words, this dotted line L11 indicates the standard boundary.

[0033] In the illustrated example, when the maximum display gradation level of the image modulation device 103 is 100%, the projection display device 1 is classified as RG2 when the projection ratio of the projection lens 104 is less than 3.5, and the projected light from the projection display device 1 is classified as RG3 when the projection ratio of the projection lens 104 is 3.5 or greater. Hereinafter, when the maximum display gradation level of the image modulation device 103 is 100% (the maximum display gradation of the display in the image modulation device 103 is the reference value), the projection ratio value that is the boundary between RG2 and RG3 (3.5 in this example) will be referred to as the "boundary value".

[0034] Furthermore, the solid line L12 shown in Graph G1 illustrates an example of controlling the maximum display gradation level of the image modulation device 103 in the projection-type display device 1 according to this embodiment. In this embodiment, the image processing unit 106 of the projection-type display device 1 switches the image quality mode near the boundary value. In this embodiment, the image processing unit 106 provides a margin and sets the threshold to 3.4, which is slightly before the boundary value of 3.5. The image processing unit 106 then controls the maximum display gradation level of the image modulation device 103 to 100% when the projection ratio of the projection lens 104 is less than the threshold of 3.4, and to 80% when the projection ratio of the projection lens 104 is greater than the threshold of 3.4. Specifically, the image processing unit 106 sets the image quality mode to "Image Quality Mode 1" when the projection ratio of the projection lens 104 is less than the threshold of 3.4, and sets the image quality mode to "Image Quality Mode 2" when the projection ratio of the projection lens 104 is greater than the threshold of 3.4. As a result, the projected light from the projection display device 1 can be maintained at RG2 across the entire projection range of the projection lens 104 (the entire range of the focal length). In the example described above, the threshold is set to 3.4, but the threshold can be any value shorter than the boundary value.

[0035] However, the above-described switching of image quality modes is only effective when the projection lens 104 has a projection ratio range that is classified as RG3 when the maximum display gradation level of the image modulation device 103 is 100%. In other words, when the maximum display gradation level of the image modulation device 103 is 100%, there is no need to switch the image quality mode for the projection lens 104 that is classified as RG3 across the entire projection ratio range. Therefore, the image processing unit 106 performs the above-described switching of image quality modes only when the type of projection lens 104 installed in its device is a specific type. The specific type is, for example, the type of projection lens 104 that has a projection ratio range that is classified as RG3 when the maximum display gradation level of the image modulation device 103 is 100%.

[0036] Figure 4 is a flowchart showing an example of the flow of display control processing performed by the projection display device 1 according to the first embodiment. The projection display device 1 performs the display control processing shown in this figure when the power is turned on (initial state), when the zoom position of the projection lens 104 is changed, or when the replacement of the projection lens 104 is detected, etc.

[0037] First, the lens recognition unit 108 recognizes the type of projection lens 104 attached to the projection display device 1, and outputs the recognized type of projection lens 104 to the image processing unit 106 (step S101).

[0038] Next, the image processing unit 106 determines whether the type of projection lens 104 is a specific type that has been set in advance (step S102). If the type of projection lens 104 is not a specific type (step S102; No), the image processing unit 106 terminates the process.

[0039] On the other hand, if the projection lens 104 is of a specific type (step S102; Yes), the detection unit 105 detects the zoom position of the projection lens 104 and outputs the focal length (projection ratio) of the projection lens 104 corresponding to the detected zoom position to the image processing unit 106 (step S103).

[0040] Next, the image processing unit 106 determines whether the focal length (projection ratio) of the projection lens 104 is less than a predetermined threshold (step S104).

[0041] The image processing unit 106 sets the image quality mode to "Image Quality Mode 1" (step S105) if the focal length (projection ratio) of the projection lens 104 is less than a predetermined threshold (step S104; Yes). That is, if the focal length (projection ratio) of the projection lens 104 is less than a predetermined threshold, the image processing unit 106 sets the maximum display gradation level of the image modulation device 103 to 100%. After that, the process ends.

[0042] On the other hand, when the focal length (projection ratio) of the projection lens 104 is greater than or equal to a predetermined threshold (step S104; No), the image processing unit 106 sets the image quality mode to "image quality mode 2" (step S106). That is, when the focal length (projection ratio) of the projection lens 104 is greater than or equal to a predetermined threshold, the image processing unit 106 sets the maximum display gradation level of the image modulation device 103 to 80%. Then, the process ends.

[0043] As described above, the projection display device 1 in the present embodiment is a projection display device 1 that irradiates a light beam from the light source unit 101 to the image modulation device 103 and enlarges and projects the image formed on the image modulation device 103 by the projection lens 104, and includes a detection unit 105 that detects the focal length of the projection lens 104, and when the detected focal length is shorter than the threshold value, sets the maximum display gradation of the display in the image modulation device 103 to the reference value, and when the detected focal length is longer than the threshold value, sets the maximum display gradation of the display in the image modulation device 103 to a limit value smaller than the reference value, and an image processing unit 106.

[0044] With such a configuration, the projection display device 1 in the present embodiment switches the maximum display gradation of the display in the image modulation device 103 to the reference value or the limit value depending on whether the focal length of the projection lens 104 is shorter or longer than the threshold value. Thereby, in a projection display device 1 with higher brightness, it is possible to maintain safety regarding brightness (for example, satisfy the conditions classified into risk group 2) over the entire focal length range of the projection lens 104 with simple control without controlling the light source light beam with respect to the projection ratio.

[0045] In addition, the projection display device 1 in the present embodiment is capable of replacing the projection lens 104, further includes a lens recognition unit 108 that recognizes the type of the projection lens 104 mounted on the device itself, and the image processing unit 106 sets the maximum display gradation of the display in the image modulation device 103 to the limit value only when a specific type of projection lens 104 is mounted.

[0046] When the reference value satisfies a predetermined condition regarding brightness (for example, a condition classified into risk group 2) throughout the entire focal length range of the projection lens 104, there is no need to set the maximum display gradation of the display in the image modulation device 103 to the limit value. Therefore, it is conceivable to set a specific type as the type of the projection lens 104 for which the reference value does not satisfy the predetermined condition in a part of the focal length. As a result, the projection display device 1 in the present embodiment can set the maximum display gradation of the display in the image modulation device 103 to the limit value only for the projection lens 104 for which the reference value does not satisfy the predetermined condition in a part of the focal length.

[0047] The threshold value is a value shorter than the focal length of the projection lens 104 at which the projection display device 1 fails to satisfy the safety standard when the display gradation in the image modulation device 103 is at the reference value, and the limit value is the display gradation that satisfies the standard throughout the entire focal length range of the projection lens 104.

[0048] With such a configuration, it is possible to limit the maximum display gradation to the limit value and control it to satisfy the standard (classified into risk group 2) before the projection light from the projection display device 1 fails to satisfy the safety standard (classified into risk group 3).

[0049] The threshold value is a value shorter than the focal length of the projection lens 104 classified into risk group 3 defined in ICE62471-5 when the display gradation in the image modulation device 103 is at the reference value, and the limit value is the display gradation for which the projection light from the projection display device is classified into risk group 2 defined in ICE62471-5 throughout the entire focal length range of the projection lens 104.

[0050] With this configuration, the projection display device 1 in this embodiment can satisfy the conditions for being classified as risk group 2 as defined in ICE 62471-5 across the entire focal length range of the projection lens 104. As a result, even a projection display device 1 with a large maximum gradation (reference value) (i.e., a high-brightness projection display device 1) can be classified as risk group 2 as defined in ICE 62471-5. Since the projection display device 1 is classified as risk group 2, there are no restrictions on sales to general consumers, and general consumers will be able to handle high-brightness projection display devices 1.

[0051] [Second Embodiment] Next, a projection-type display device and projection-type display method according to a second embodiment of the present invention will be described. The configuration of the projection-type display device 1 in this embodiment is the same as in the first embodiment, so its description will be omitted.

[0052] In the projection-type display device 1 of the first embodiment, the image quality mode switches frequently in a short period of time when the projection ratio of the projection lens 104 is repeatedly increased or decreased in a short period of time within a narrow range near a threshold. Also, when the firmware periodically acquires the zoom position, the detected value of the potentiometer may vary slightly even if the zoom position has not changed. In such cases as well, when the projection ratio of the projection lens 104 is near a threshold, the image quality mode similarly switches frequently in a short period of time. When the image quality mode switches frequently in a short period of time, the brightness of the image projected onto the projection surface is unstable. Therefore, the projection-type display device 1 of this embodiment differs from the first embodiment in that it switches the image quality mode using different thresholds depending on whether the focal length of the projection lens 104 is changed to be longer or shorter.

[0053] Figure 5 is a graph illustrating the display control processing performed by the projection-type display device 1 according to the second embodiment. In graph G2 shown in this figure, the vertical axis represents the maximum display gradation level of the image modulation device 103 (unit: % (percent)), and the horizontal axis represents the projection ratio of the projection lens 104. The dotted line L21 shown in graph G2 indicates the boundary line between RG2 and RG3. In the illustrated example, when the maximum display gradation level of the image modulation device 103 is 100%, the projected light from the projection-type display device 1 is classified as RG2 when the projection ratio of the projection lens 104 is less than 3.5, and the projected light from the projection-type display device 1 is classified as RG3 when the projection ratio of the projection lens 104 is 3.5 or greater.

[0054] Furthermore, the solid line L22 shown in graph G2 illustrates an example of controlling the maximum display gradation level of the image modulation device 103 in the projection-type display device 1 according to this embodiment. When the projection ratio of the projection lens 104 is changed to be larger after the change than before, the image processing unit 106 sets the image quality mode to "Image Quality Mode 1" while the projection ratio is smaller than the first threshold F1 (for example, 3.4), and to "Image Quality Mode 2" when it becomes larger than the first threshold F1. Conversely, when the projection ratio of the projection lens 104 is changed to be smaller after the change than before, the image processing unit 106 sets the image quality mode to "Image Quality Mode 2" while the projection ratio is larger than the second threshold F2 (for example, 3.2) which is different from the first threshold F1, and to "Image Quality Mode 1" when it becomes smaller than the second threshold F2.

[0055] By incorporating hysteresis characteristics in this way, even when the projection ratio repeatedly increases and decreases within a narrow range near the boundary value, or when there is variation in the detection value of the potentiometer, it is possible to suppress rapid switching of the image quality mode and suppress unintended changes in the brightness of the image. As a result, the projected light from the projection display device 1 can be maintained at RG2 across the entire projection ratio range of the projection lens 104.

[0056] In the example described above, the first threshold F1 is greater than the second threshold F2, but this is not limited to this case; the second threshold F2 may also be greater than the first threshold F1.

[0057] Figure 6 is a graph illustrating an example of the image quality mode in the initial state of the projection-type display device 1 according to the second embodiment. In graph G3 shown in this figure, the vertical axis represents the maximum display gradation level of the image modulation device 103 (unit: % (percent)), and the horizontal axis represents the projection ratio of the projection lens 104. The dotted line L21 and solid line L22 shown in graph G3 are the same as those in graph G2, so their explanation is omitted.

[0058] In this example, the video processing unit 106 sets the image quality mode to "image quality mode 2" if the projection ratio of the projection lens 104 (hereinafter referred to as the "initial value") detected when the projection display device 1 is powered on or in an initial state is between the first threshold F1 and the second threshold F2. That is, if the "initial value" of the projection ratio of the projection lens 104 is between the first threshold F1 and the second threshold F2, the video processing unit 106 sets the maximum display gradation level of the image modulation device 103 to 100% (using the initial value F0 of the maximum display gradation as the reference value).

[0059] Figure 7 is a graph illustrating another example of the image quality mode in the initial state of the projection display device 1 according to the second embodiment. In graph G4 shown in this figure, the vertical axis represents the maximum display gradation level of the image modulation device 103 (unit: % (percent)), and the horizontal axis represents the projection ratio of the projection lens 104. The dotted line L21 and solid line L22 shown in graph G4 are the same as those in graph G2, so their explanation is omitted. In this example, the image processing unit 106 sets the image quality mode to "image quality mode 1" when the "initial value" of the projection ratio of the projection lens 104 is between the first threshold F1 and the second threshold F2. That is, when the "initial value" of the projection ratio of the projection lens 104 is between the first threshold F1 and the second threshold F2, the image processing unit 106 sets the maximum display gradation level of the image modulation device 103 to 80% (limiting the initial value of the maximum display gradation F0).

[0060] Figure 8 is a flowchart showing an example of the flow of display control processing performed by the projection display device 1 according to the second embodiment. The projection display device 1 performs the display control processing shown in this figure when power is turned on to the projection display device 1 (initial state), when the zoom position of the projection lens 104 is changed, or when the replacement of the projection lens 104 is detected, etc.

[0061] The processes in steps S201 to S203 are the same as those in steps S101 to S103 in the first embodiment, so their explanation will be omitted.

[0062] Following step S203, the image processing unit 106 determines whether the changed focal length of the projection lens 104 is longer than the original focal length (step S204).

[0063] If the focal length of the projection lens 104 is changed to a longer value (step S204; Yes), the image processing unit 106 sets the threshold for switching the image quality mode to the first threshold F1 (step S205). Then, the process proceeds to step S207.

[0064] On the other hand, if the focal length of the projection lens 104 is changed to a shorter value (step S204; No), the image processing unit 106 sets the threshold for switching the image quality mode to the second threshold F2 (step S206).

[0065] Next, the image processing unit 106 determines whether the focal length (projection ratio) of the projection lens 104 is less than the threshold set in step S205 or step S206 (step S207).

[0066] The image processing unit 106 sets the image quality mode to "Image Quality Mode 1" (step S208) if the focal length (projection ratio) of the projection lens 104 is less than a threshold (step S207; Yes). That is, if the focal length (projection ratio) of the projection lens 104 is less than a threshold, the image processing unit 106 sets the maximum display gradation level of the image modulation device 103 to 100%. After that, the process ends.

[0067] On the other hand, if the focal length (projection ratio) of the projection lens 104 is greater than or equal to a threshold (step S207; No), the image processing unit 106 sets the image quality mode to "image quality mode 2" (step S209). That is, if the focal length (projection ratio) of the projection lens 104 is greater than or equal to a predetermined threshold, the image processing unit 106 sets the maximum display gradation level of the image modulation device 103 to 80%. After that, the processing ends.

[0068] As described above, the projection lens 104 of the projection display device 1 in this embodiment has a changeable focal length. When the focal length of the projection lens 104 is changed to be longer than before, the image processing unit 106 sets the maximum display gradation of the image modulation device 103 to a limit value when the focal length of the projection lens 104 becomes longer than a first threshold. When the focal length of the projection lens 104 is changed to be shorter than before, the image processing unit 106 sets the maximum display gradation of the image modulation device 103 to a reference value when the focal length of the projection lens 104 becomes shorter than a second threshold which is different from the first threshold.

[0069] By incorporating hysteresis characteristics in this way, even when the projection ratio repeatedly increases and decreases within a narrow range near the boundary value, or when there is variation in the detection value of the potentiometer, it is possible to suppress rapid switching of the maximum display gradation of the display in the image modulation device 103 and suppress unintended changes in the brightness of the image.

[0070] Furthermore, in this embodiment, the image processing unit 106 of the projection display device 1 sets the maximum display gradation of the display in the image modulation device 103 to a reference value when the initial value of the focal length of the projection lens 104 is between the first threshold and the second threshold.

[0071] With this configuration, the projection display device 1 in this embodiment can display in "image quality mode 1" with high gradation in its initial state.

[0072] Furthermore, in this embodiment, the image processing unit 106 of the projection display device 1 sets the maximum display gradation of the display in the image modulation device 103 to a limit value when the initial value of the focal length of the projection lens 104 is between the first threshold and the second threshold.

[0073] With this configuration, the projection display device 1 in this embodiment can display in "image quality mode 2," which has a lower gradation than "image quality mode 1," in its initial state.

[0074] [Third Embodiment] Next, a projection-type display device according to a third embodiment of the present invention will be described. The configuration of the projection-type display device 1 in this embodiment is the same as in the first embodiment, so its description will be omitted.

[0075] Figure 9 is a graph illustrating the display control process performed by the projection-type display device 1 according to the third embodiment. In graph G5 shown in this figure, the vertical axis represents the maximum display gradation level of the image modulation device 103 (unit: % (percent)), and the horizontal axis represents the projection ratio of the projection lens 104. The dotted line L21 and solid line L22 shown in graph G4 are the same as those in graph G2, so their explanation is omitted.

[0076] The dashed line L53 shown in Graph G5 indicates the image quality mode before acquiring data on the maximum and minimum zoom positions of the projection lens 104 that determines the projection ratio. In this embodiment, the image processing unit 106 sets the image quality mode to "Image Quality Mode 2" across the entire projection ratio range of the projection lens 104 before acquiring data on the maximum and minimum zoom positions of the projection lens 104 that determines the projection ratio. Then, after acquiring data on the maximum and minimum zoom positions, the image processing unit 106 executes the display control processing in the first or second embodiment.

[0077] With this configuration, the projection display device 1 in this embodiment always sets the image quality mode to "image quality mode 2" when the projection ratio of the projection lens 104 is not detected. This prevents the maximum display gradation of the display in the image modulation device 103 from becoming the reference value when the projection ratio is greater than the boundary value, and prevents the projection display device 1 from being unintentionally classified as RG3.

[0078] [Fourth Embodiment] Next, a projection display device according to the fourth embodiment of the present invention will be described. The configuration of the projection display device 1 in this embodiment is the same as in the first embodiment, so its description will be omitted. The light source unit 101 in this embodiment is a laser light source including semiconductor lasers and solid-state lasers. Furthermore, the projection display device 1 according to this embodiment satisfies the conditions for proceeding to evaluation according to ICE 62471-5 as specified in ICE 30825-1 (3rd edition).

[0079] Figure 10 is a graph illustrating the display control processing performed by the projection-type display device 1 according to the fourth embodiment. In graph G6 shown in this figure, the vertical axis represents the maximum display gradation level of the image modulation device 103 (unit: % (percent)), and the horizontal axis represents the projection ratio of the projection lens 104. The dotted line L61 shown in graph G6 indicates the boundary line between laser class 1 and laser class 4 as defined in IEC 60825-1. For each projection ratio, the maximum display gradation level below this dotted line L61 is laser class 1, and the maximum display gradation level above this dotted line L61 is laser class 4. In other words, this dotted line L61 indicates the standard boundary.

[0080] In the illustrated example, when the maximum display gradation level of the image modulation device 103 is 100%, the projection display device 1 is classified as laser class 1 when the projection ratio of the projection lens 104 is less than 3.5, and the projection display device 1 is classified as laser class 4 when the projection ratio of the projection lens 104 is 3.5 or greater. In other words, the boundary value in this example is 3.5.

[0081] In the first to third embodiments, the threshold is set so that the projection display device 1 is classified into risk group 2 as defined in IEC 62471-5. However, in this embodiment, the threshold is set so that the projection display device 1 is classified into laser class 1 in the evaluation according to ICE 62471-5, which is different from the first to third embodiments. The other display control processing of the projection display device 1 in this embodiment is the same as in the first to third embodiments, so its explanation is omitted.

[0082] As described above, the projection display device 1 in this embodiment satisfies the conditions for transitioning to evaluation according to ICE 62471-5 as defined in ICE 30825-1 (3rd edition), and includes a laser as a light source. Furthermore, the limit value in this embodiment is that the projection display device 1 has a gradation that is classified as laser class 3R or lower as defined in IEC 60825-1 across the entire focal length range of the projection lens 104.

[0083] With this configuration, the projection display device 1 in this embodiment, when the light source includes a laser, can satisfy the conditions for being classified as laser class 3R or less as defined in IEC 60825-1 across the entire focal length range of the projection lens 104. As a result, even a projection display device 1 with a large maximum gradation (reference value) (i.e., a high-brightness projection display device 1) can be classified as laser class 3R or less as defined in IEC 60825-1. Since the projection display device 1 is classified as laser class 3R or less as defined in IEC 60825-1, there are no restrictions on sales to general consumers, making it possible for general consumers to handle high-brightness projection display devices 1.

[0084] Alternatively, construction management may be performed by recording a program for realizing all or part of the functions of the projection display device 1 shown in Figure 1 onto a computer-readable recording medium, and then loading and executing the program recorded on this recording medium into a computer system. The term "computer system" here includes hardware such as the operating system and peripheral devices.

[0085] Furthermore, "computer system" includes the homepage provisioning environment (or display environment) if a WWW system is being used. "Computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and storage devices such as hard disks built into computer systems. "Computer-readable recording medium" also includes volatile memory within server and client computer systems that retain programs for a certain period of time. The above program may only implement a part of the aforementioned functions, and may also be implemented in combination with programs already recorded in the computer system. The above program may also be stored on a designated server and distributed (downloaded, etc.) via a communication line in response to requests from other devices.

[0086] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0087] Figure 11 is a block diagram showing the minimum configuration of a projection-type display device 50 according to an embodiment of the present invention. As shown in this figure, the projection-type display device 50 comprises at least a detection unit 51 and an image processing unit 52.

[0088] The detection unit 51 detects the focal length of the projection lens. The image processing unit 52 sets the maximum display gradation of the display in the image modulation device to a predetermined reference value if the detected focal length is shorter than a predetermined threshold, and sets the maximum display gradation of the display in the image modulation device to a limit value smaller than the reference value if the detected focal length is longer than the threshold.

[0089] 1, 50... Projection-type display device 101... Light source unit 102... Illumination optical system 103... Image modulation device 104... Projection lens 105, 51... Detection unit 106, 52... Image processing unit 107... Light source drive control unit 108... Lens recognition unit

Claims

1. A projection-type display device that irradiates an image modulation device with a light beam from a light source and magnifies and projects an image formed on the image modulation device using a projection lens, comprising: a detection unit for detecting the focal length of the projection lens; and an image processing unit that, when the detected focal length is shorter than a threshold, sets the maximum display gradation of the display on the image modulation device to a reference value, and when the detected focal length is longer than the threshold, sets the maximum display gradation of the display on the image modulation device to a limit value smaller than the reference value.

2. The projection lens has a changeable focal length, and the image processing unit sets the maximum display gradation of the display in the image modulation device to the limit value when the focal length of the projection lens is changed to be longer than before the change, and sets the maximum display gradation of the display in the image modulation device to the reference value when the focal length of the projection lens is changed to be shorter than before the change, and sets the maximum display gradation of the display in the image modulation device to the reference value when the focal length of the projection lens is shortened to be shorter than before the change, 3. The projection display device according to claim 2, wherein the first threshold is greater than the second threshold.

4. The projection lens is replaceable, and the device further comprises a lens recognition unit that recognizes the type of projection lens installed in the device, and the image processing unit sets the maximum display gradation of the display in the image modulation device to the limit value only when a projection lens of a specific type is installed.

5. The projection display device according to claim 2, wherein the image processing unit sets the maximum display gradation of the display in the image modulation device to the reference value when the initial value of the focal length of the projection lens is between the first threshold and the second threshold.

6. The projection display device according to claim 2, wherein the image processing unit sets the maximum display gradation of the display in the image modulation device to the limit value when the initial value of the focal length of the projection lens is between the first threshold and the second threshold.

7. The projection display device according to claim 1, wherein the threshold is a value shorter than the focal length of the projection lens at which the projection display device ceases to meet safety standards when the display gradation in the image modulation device is the reference value, and the limit value is a display gradation that satisfies the standard over the entire range of the focal length of the projection lens.

8. The projection display device according to claim 1, wherein the threshold is a value shorter than the focal length of the projection lens that classifies the projection display device into risk group 3 as defined in ICE 62471-5 when the display gradation in the image modulation device is the reference value, and the limit value is a display gradation that classifies the projection display device into risk group 2 as defined in ICE 62471-5 over the entire range of the focal length of the projection lens.

9. The projection display device according to claim 1, wherein the light source includes a laser, and the limit value is such that the projection display device is classified as a laser class 3R or less as defined in IEC 60825-1 over the entire range of the focal length of the projection lens.

10. The projection display device according to claim 9, which satisfies the conditions for transitioning to evaluation according to ICE 62471-5 as defined in ICE 30825-1 (3rd edition), wherein the threshold is a value shorter than the focal length of the projection lens that classifies the projection display device into laser class 4 as defined in IEC 60825-1 when the display gradation of the image modulation device is the reference value, and the limit is a display gradation that classifies the projection display device into laser class 1 as defined in IEC 60825-1 over the entire range of the focal length of the projection lens.

11. A projection-type display method in a projection-type display device, which irradiates an image modulation device with a light beam from a light source and magnifies and projects an image formed on the image modulation device using a projection lens, wherein the projection method includes detecting the focal length of the projection lens, setting the maximum display gradation of the display on the image modulation device to a predetermined reference value if the detected focal length is shorter than a threshold, and setting the maximum display gradation of the display on the image modulation device to a limit value smaller than the reference value if the detected focal length is longer than the threshold.

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