Efficient Encoding of Colored Pictures in R, G, B Components

The encoding of colored pictures in components has attracted a lot of attention. In this paper, for their efficient transmission in the 2-3 bit/pel range, the direct encoding of the red (
R
), green (
G
), and blue (
B
) primaries is investigated. Differential PCM with vector quantization is used and the encoding efficiencies are compared to the similar result obtained using the properly converted luminance (
Y
) and chrominance (
I,Q
) component signals. A new quantization scheme is proposed for
RGB
encoding to improve the picture quality. As a result, it is shown that
RGB
encoding can attain a comparable or slightly higher encoding efficiency as compared to
YIQ
encoding, and a higher resolution can be obtained for strong color edges defined by the primary colors, but the resulting picture quality is much noisier; thus, it is better suited for such applications in which the edges of primary colors play important roles, such as in graphics materials. An adaptive vector quantization is introduced in order to apply the proposed
RGB
encoding scheme to a wider range of pictures. The quantity called activity is introduced, considering the form of the predictor used. The optimum adaptive scheme is derived and its effectiveness is verified through simulations.