The objective image quality evaluation of DCT(discrete cosine transform) compressed images is usually achieved using MSE(mean square error) and PSNR(peak signal to noise ratio) with the geometric degradation of images out of consideration

which is the very key to the optical measurement system based on position information. DCT compression experiemnts made with two images with high spatial redundancy show that MSE and PSNR do not change much under 4?4 processing block and 1:2 compression ratio

but there is a geometric degradation of 1 or 2 pixels; considering the total error of the optical measurement system is generally only 1 or 2 pixels

a change in position of more than 1 pixel resulting from DCT compression will have a significant influence on the accuracy of the measurement system. A good deal of attention should

therefore

be paid to geometric degradation during DCT compression.