METHOD OF COMPRESSING IMAGE DATA HAVING A UNIFORM BACKGROUND TINT

The method of compressing image data having a background tint is carried out by general apparatus 10. Greyscale image data containing stroke based symbols is retrieved to form a pixel data stream 10S of digital image data. The stream has stroke foreground pixels and non-stroke background pixels. The greyscale image data has levels of greyscale extending along an intensity scale from a minimum low intensity level 34L to a maximum high intensity level 34H. The stroke foreground pixels of the digital image data are predominantly pixels at the maximum greyscale level, and the non-stroke background pixels are predominantly pixels at the minimum greyscale level. A clamping range 34R of low intensity greyscale levels is determined extending continuously from the minimum greyscale level up to a greyscale level at least as great as the predominant level forming the non-stroke background pixels. A low intensity greyscale clamping level greater than the minimum greyscale level is determined. The greyscale levels of the retrieved image data that are within the clamping range are clamped to the low intensity clamping level to provide a uniform shade of low intensity background tint. The clamped digital image data is compressed to reduce the data storage requirements therefor, and entered into data storage device 10M.