Heatmap shows where pure-white pixels drift after JPEG compression

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A white-background sneaker photo saved as a JPEG at quality 85 lost exactly-255 values, with 10,403 pixels changing and most of them clustered along the shoe outlines. The author built a heatmap and distance count to show the drift sits close to the subject rather than across open white. Counting drift at lower thresholds shows most changes are only one or two levels below pure white, though a few background pixels fall as low as 239. The author warns that whole-image percentages can understate the problem because they also include bright pixels from the shoe itself. The test was run to check compliance with Amazon's requirement for RGB 255 main images.

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