Lossless compression of pre-press images using a novel colour decorrelation technique

Abstract

In the pre-press industry colour images have both a high spatial and a high colour 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. Most existing compression schemes operate on gray-scale images. How­ever, in the case of colour images higher compression ratios can be achieved by exploiting inter-colour redundancies. In this paper a new lossless colour transform is proposed, based on the KLT. This transform removes redundancies in the colour 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 colour transform typically saves about a half to two bit per pixel, compared to a purely predictive scheme. The results also suggest that combining the proposed KLT scheme with the state-of-the-art CALIC gray-scale-only coder could significantly increase the compression ratio of that scheme.