Two algorithms are presented for compressing image documents, with a high
compression ratio for both colour and monochromatic compound document images. The proposed
algorithms apply a new method of segmentation to separate the text from the image in a compound
document in which the text overlaps the background. The segmentation method classifies document
images into three planes: the text plane, the background (non-text) plane and the text’s colour plane,
each of which are processed using different compression techniques. The text plane is compressed
using the pattern matching technique, called JB2. Wavelet transform and zerotree coding are used
to compress the background plane and the text’s colour plane. Assigning bits for different planes
yields high-quality compound document images with both a high compression ratio and well
presented text. The proposed algorithms greatly outperform two well known image compression
methods, JPEG and DjVu, and enable the effective extraction of the text from a complex
background, achieving a high compression ratio for compound document images.
