Image processing apparatus for preventing occurrence of moire in a reconstructed image

An image processing apparatus for image compression and decompression, in which an image is grouped into a set of blocks, image data of each block is converted into a number of coefficients through discrete cosine transformation, the coefficients are quantized so as to generate a compressed image, and the compressed image is converted into a reconstructed image with respect to each block through de-quantization and through inverse discrete cosine transformation, said apparatus comprising:

• a) smoothing means, including a plurality of soothing filters having mutually different smoothing effects, for smoothing image data of the reconstructed image by using a smoothing filter selected from among the plurality of smoothing filters based on a smoothing filter selector signal, and for providing smoothed image data;
• b) filter selector signal generating means for generating the smoothing filter selection signal to which the smoothing means is responsive, the filter selector signal generating means including:
• 1) averaging means for producing a set of values of averages of the coefficients with respect to a plurality of blocks in the reconstructed image, and for generating a distribution of the averages of the coefficients for a target block;
• 2) discrimination means, responsive to the averaging means, for analyzing the distribution of the averages of the coefficients for the target block, for determining whether or not peak values in the distribution are substantially on a diagonal line of the target block, the diagonal line extending from a corner of the distribution representing a lowest-order position to a corner representing a highest-order position in the target block, and for generating the smoothing filter selection signal;
• and
• 3) a line memory, responsive to the discrimination means, for receiving the smoothing filter selection signal, and providing the smoothing filter selection signal to the smoothing means;
• c) a halftone imaging means, connected to an output of the smoothing means, for receiving the smoothed image data and for subjecting the smoothed image data to a halftone imaging process, and for providing output image data;
• and
• d) output means, connected to an output of the halftone imaging means to receive the output image data, for providing a processed image which is derived from the reconstructed image.