Vector Error Diffusion Palette for Bi-tonal Print Graininess
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Solution Overview
Problem
Bi-tonal printing engines struggle to minimize graininess in image highlight areas, as existing methods often result in darker secondary colors being output, leading to noticeable graininess.
Innovation Solution
The method employs vector error diffusion with a specially generated color-value palette that excludes white values and includes fictional C′, M′, Y′ values, using spectrophotometric analysis to correlate input-color-space pixel values with C, M, Y device output-color-space values, and applies luminance thresholding to suppress graininess in highlight regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional vector error diffusion is used with bi-tonal printing engines, then color images can be printed, but graininess appears in highlight areas due to darker secondary colors being output
Solution Approach 1:
The patent changes the parameter space by introducing fictional C′, M′, Y′ color values that lie between white and the actual C, M, Y values. This creates a expanded color value palette that allows the error diffusion algorithm to select lighter primary colors instead of darker secondary colors in highlight areas, thereby reducing graininess while maintaining printing capability
Solution Approach 2:
The fictional C′, M′, Y′ color values act as intermediaries between white and the actual C, M, Y color values. These intermediary values provide transition states that enable smoother error diffusion in highlight areas, preventing the direct selection of darker secondary colors that cause graininess
2Adaptability or versatility
If a complete color-value palette including white values is used, then all color ranges can be represented, but graininess increases in highlight regions
Solution Approach 1:
The patent extracts white values from the color-value palette used for error diffusion processing. By removing white values from the palette (while still supporting them as output), the algorithm is forced to use the fictional C′, M′, Y′ intermediary values instead, which prevents graininess in highlight areas while maintaining the ability to represent the full color range through the spectral analysis approach
3Stability of the object's composition
If pixel-value interpolation is used to smooth transitions, then color continuity is improved, but processing complexity and time increase
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing the fictional C′, M′, Y′ color values in the palette before processing. This pre-computation allows the error diffusion algorithm to directly select from these prepared intermediary values without requiring runtime interpolation calculations, thereby maintaining color continuity while reducing processing complexity
Data Source
AI summary
A vector error diffusion (VED) method employable in cycles with respect to a hi-tonal color printing engine which prints bi-tonal color images in a device output color space. The method generally includes (a) acquiring input color-image data which is characterized with an input color space, (b) processing, with available pre-established VED accumulated error data, such input data to produce a VED-processed input color-image data stream, (c) from such VED-processed input color-image data stream, creating, without employing interpolation, a VED-processed output color-image data stream which is characterized by the mentioned device output color space, and which is suitable for delivery to and use by the mentioned printing engine, and (d) changing, as appropriate for the next cycle, the VED accumulated error data which will be employed in that next cycle as pre-established VED accumulated error data.