OPPapers.com

A Color Transformation For The Compression Of Cmyk

ABSTRACT
A CMYK image is often viewed as a large amount of device-dependent data ready to be printed. In several circun-
stances, CMYK data needs to be compressed, but the conversion to and from device-independent spaces is imprecise
at best. In this paper, with the goal of compressing CMYK images, color space transformations were studied. In
order to have a practical importance we developed a a new transformation to a YYCC color space, which is device-
independent and image-independent, i.e. a simple linear transformation between device-dependent color spaces. The
transformation from CMYK to YYCC was studied extensively in image compression. For that a distortion measure
that would account for both device-dependence and spatial visual sensitivity has been developed. It is shown that
transformation to YYCC consistently outperforms the transformation to other device-dependent 4D color spaces
such as YCbCrK, while being competitive with the image-dependent KLT-based approach. Other interesting con-
clusions were also drawn from the experiments, among them the fact that color transformations are not always
advantageous over independent compression of CMYK color planes and the fact that chrominance subsampling is
rarely advantageous.
1. INTRODUCTION
Images for monitor display are commonly stored or transmitted in popular color spaces such as RGB, CIELAB,
YUV, YCbCr, etc..1,2 Images to be printed are commonly rendered in a subtractive color space such as CMYK.1,2
Sometimes documents contain pictures in other color spaces which are then converted to CMYK for printing.
It is often necessary to compress CMYK images for a number of reasons, such as bandwidth or memory reduction.
Fig. 1 shows a printing system path in which a CMYK image bitmap is generated and possibly compressed. JPEG3
is a standard for image compression and is widely used. Other compressors such as SPIHT4 are becoming very
popular and work is underway to define a new...