Tile based color space transformation

Abstract

A system and method for tile type based color space transformation improves the performance and image quality of multifunction devices. The disclosed embodiments transform an input image on a tile by tile basis. If a tile is detected as neutral, simple 1D L* to CMYK Tone Reproduction Curves or Look-Up-Tables are used to convert the input pixels of the tile in L*a*b* to output pixels in CMYK. If a tile is detected as containing color content, then the input pixels are chrominance adjusted and subsequently converted to CMYK using regular tetrahedral interpolation.

Description

BACKGROUND[0001]The subject disclosure relates to the printing arts, the copying / scanning arts, the image processing arts, the color processing arts, spot color printing, and the like.[0002]While historically images were captured using photographic film, modern digital devices (such as scanners, cameras, etc.) capture images as pixels electronically, and most such digital devices capture images in a color space referred to as RGB, or red-green-blue color space. The RGB color space is utilized by image capture devices because such devices commonly include sensors that distinguish between the red, green, and blue colors.[0003]When processing images captured by digital devices to make color corrections, remove undesirable artifacts, improve image resolution, suppress background, prepare images for printing or display, etc. (which is sometimes referred to as image path processing) it is often useful to first convert the electronic images into a color space that is device independent, su...

AI Technical Summary

Benefits of technology

[0013]Accordingly, described herein in various embodiments is a tile type based color space transformation method that improves the speed of image processing. Specifically, the color space transformation method is selected on a tile by tile basis. In the disclosed method, if a tile is detected as neutral, simple 1D L* to CMYK TRCs are used to convert the input pixels in CIEL*a*b* to output pixels in CMYK; if a tile is detected as containing color content, then the input pixels are chrominance adjusted first and then converted to CMYK using formula which is more complex than 1D table looking up, for example and without limitation, regular tetrahedral interpolation. The disclosed method offers a significant savings in computation time for most jobs as 1D look-up tables are faster to execute than interpolation methods by at least an order of magnitude. For example, tetrahedral interpolation of an 8.5″×11″page at 600 dpi may process in about ˜300 msec while 1D look up tables of the same page may process in ˜30 msec. With the chrominance adjustment step, which sets the a* value and the b* value to 128 for neutral pixels, and properly designed 1D L* to CMYK TRCs, the disclosed methods and systems avoid potential switching artifacts due to different treatments for neutral pixels. The disclosed method can also be used in other conversions such as CIELab to YCbCr conversion. The disclosed methods fit nicely into tile type based processing frameworks in software based image path. There is no extra overhead in tile based neutral detection as the neutral based detection is a needed step in page-level neutral / color detection.

Problems solved by technology

Color space transformations using methods and formulae more complex than 1D look up tables, such as for example and without limitation tetrahedral interpolation, are one of the more computationally expensive functions in color image path for digital copiers and multifunction devices.

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