On Color Transforms and Bit Allocation for Optimal Subband Image

Evgeny Gershikov and Moshe Porat,
Department of Electrical Engineering, 
Technion - Israel Institute of Technology 
Haifa 32000, Israel


Although subband transform coding is a useful approach to image
compression and communication,the performance of
this method has not been analyzed so far for color images,especially
when the selection of color components is considered.
Obviously,the RGB components are not suitable for such a compression
method due to their high inter-color correlation.
On the other hand,the common selection of YUV or YIQ is rather
arbitrary and in most cases not optimal.In this work
we introduce a rate distortion model for color image compression and
employ it to nd the optimal color components and
optimal bit allocation (optimal rates)for the compression.We show that
the DCT (discrete cosine transform)can be used
to transform the RGB components into an ef cient set of color
components suitable for subband coding.The optimal rates
can be also used to design adaptive quantization tables in the coding
stage with results superior to xed quantization
tables.Based on the presented results,our conclusion is that the new
approach can improve presently available methods
for color image compression and communication.

Elsevier Signal Processing: Image Communicatio, Vol. 22, pp. 1-18 (2007). 

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