Well, I disagree on both counts. I am not going to design all my websites over a constraint that images should be a multiple of 8 in both dimensions. In other words, I don't want to test the sweet spot of JPEG, I want to test its performance in real life.
Also, PSNR is a measure of the distance between two images. It's cool. What I want is to see whether the images "look" similar or not. I can find two images that look exactly the same and that have a PSNR greater than two other images that look greatly different. In other words, PSNR is a poor approximation of the visual similarity of two images. That's not what I'm looking for. For example, PSNR doesn't take into account the density of a screen when comparing two images while I just showed that it is greatly different at 100dpi vs 200dpi.
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