Lossless Compression of Pre-press Images Using a Novel Colour Decorrelation Technique

In the pre-press industry color images have both a high spatial and a high color resolution. Such images require a considerable amount of storage space and impose long transmission times. Data compression is desired to reduce these storage and transmission problems. Because of the high quality requirements in the pre-press industry only lossless compression is acceptable. Most existing lossless compression schemes operate on gray-scale images. In this case the color components of color images must be compressed independently. However, higher compression ratios can be achieved by exploiting inter-color redundancies. In this paper a new lossless color transform is proposed, based on the Karhunen-Lo eve Transform (KLT). This transform removes redundancies in the color representation of each pixel and can be combined with many existing compression schemes. In this paper it is combined with a prediction scheme that exploits spatial redundancies. The results proposed in this paper show that the color transform eeectively decorrelates the color components and that it typically saves about a half to two bit per pixel, compared to a purely predictive scheme.