Method and apparatus for providing bit-rate reduction and reconstruction of image data using dither arrays

摘要

An apparatus and method for providing bit-rate reduction and reconstruction of image data. Bit-rate reduction of 32-bit CMYK combinations into 16-bit code words is performed on a pixel by pixel basis by stepwise calculations or by using LUTs. Bit-rate reduction takes place during PostScript TM interpretation where the output image pixels are generated in a possibly arbitrary order. Bit expansion from 16-bit code words to 32-bit data for 8 bits per component of the CMYK image values is performed while real time printing, preferably by direct table look up. During bit-rate reduction, the image data may be non-linearly corrected to compensate for perceptual non-uniformities and for non-linearities in the input/output relationship of the reproduction device. Quantization and coding may be accomplished by thresholding the non-linearly corrected image data by values from a dither array. The coded image is stored in the frame buffer and subsequently retrieved, de-dithered, dequantized and inversely transformed for the perceptual non-linearity before printing.