Printers process large quantity of data when printing. For example, printing on an A3 size (297 mm 420 mm) at
300 dpi resolution requires 17.4 million pixels, and about 66 Mbytes in a 32-bits/pixel-color image composed of Yellow
(Y), Magenta (M), Cyan (C) and Black components. Containing such a large capacity of Random Access Memories
(RAMs) in a printer causes an increase in both cost and the size of memory circuits. Thus, image compression techniques
are examined in this study to cope with these problems.
A still-image coding, being standardized by JPEG (Joint Photographic Experts Group)', will presumably be utilized
for image communications or image data bases. The JPEG scheme can compress natural images efficiently; it is unsuitable
for text or Computer Graphics (CG) images for degradation of restored images. This scheme, therefore, cannot be implemented
for printers which require good image quality.
We studied codings which are more suitable for printers than the JPEG scheme2. Two criteria were considered to
select a coding scheme suitable for printers: i.e., (1) no visible degradation of input printer images; (2) capability of image
edition. Especially in terms of criteria (2), a fixed-length coding was adopted; an arbitrary pixel data code can be easily
read out of an image memory. Then we implemented an image coding scheme in our new sublimation full color printer.
Input image data are compressed by coding before being written into an image memory.