Dynamic Range Compression for Natural Print Tonality
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Solution Overview
Problem
The dynamic range of printed images illuminated with high-luminance light often results in unnatural tonality and contrast, particularly in dark regions, due to the compression of luminance values, which prevents sufficient tone expression.
Innovation Solution
An image processing apparatus and method that dynamically converts the luminance range of captured images by obtaining reference values based on print medium and observation environment information, generating a conversion line to match the input and output luminance signals, ensuring suitable contrast and tonality across the entire image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If dynamic range compression is performed to match the narrower output dynamic range, then the output image can be displayed on standard printing devices, but the tonality in dark regions becomes unnatural and contrast is lost
Solution Approach 1:
The patent applies different compression rates to different luminance regions of the image. Specifically, the dark region compression rate is set lower than the bright region compression rate, allowing dark regions to retain more tonal information and contrast while still achieving overall dynamic range compression for standard device compatibility.
Solution Approach 2:
The patent dynamically adjusts compression parameters based on the input image's dynamic range characteristics and the expected observation environment. The control unit varies the compression rate according to luminance levels, applying stronger compression to bright regions and weaker compression to dark regions, thereby maintaining natural tonality across the entire image.
2Illumination intensity
If high-luminance light is used for illumination exhibition to widen the perceivable dynamic range, then more luminance information can be perceived, but dark regions become overly bright and lose their intended tonality
Solution Approach 1:
The patent applies preliminary compensation processing to dark regions before printing, anticipating the effect of high-luminance illumination. By reducing the compression rate for dark regions and adjusting their luminance values upward in advance, the patent counteracts the brightening effect that will occur during illumination exhibition, thereby maintaining the intended dark region tonality when viewed under high-luminance light.
3Reliability
If a fixed anchor point is used for dynamic range compression to maintain creator's intent, then the reference luminance value is preserved, but the overall contrast and tonality of the image deteriorates
Solution Approach 1:
The patent replaces the fixed anchor point approach with dynamic compression rate adjustment. Instead of forcing a single reference luminance value to remain fixed, the system dynamically varies compression rates across different luminance regions while maintaining the overall dynamic range compression. This allows the image to preserve natural contrast and tonality across all regions rather than sacrificing overall quality to maintain a single anchor point.
Data Source
AI summary
An image processing apparatus includes an obtaining unit to obtain image data and a dynamic range conversion unit to convert an input luminance signal included in the image data into an output luminance signal for an image printing apparatus by using a conversion parameter. A dynamic range of luminance of the converted image data is narrower than that of the unconverted image data before the dynamic range conversion. When the input luminance signal indicates an input black reference luminance value, the output luminance signal indicates an output black reference luminance value, and, when the input luminance signal indicates a predetermined reference input luminance value, the output luminance signal indicates a reference output luminance value, the reference output luminance value being a value calculated based on the predetermined reference input luminance value and the output black reference luminance value for observing a print product to be printed by the printing apparatus.