Estimating relative objective quality among images compressed from the same original

This paper presents a new method for estimating the relative compression distortion among images encoded from the same original. Increasingly, many compressed versions of the same image are available over the Internet, but users may not have access to the original to measure their objective quality. We propose to cross-check each image against the quantization constraints of another version and obtain a conservative estimation of the difference in mean squared error (ΔMSE), indicating the relative objective quality between these images. Our proposed method is able to judge the relative quality correctly among compressed images with PSNR difference of as little as 0.5 dB, and it is applicable to images in mixed compression formats, such as JPEG and JPEG2000.