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File Formats: What the Encoder Did Before You Read the Pixels

Lesson 5 of The Image as Data. A JPEG quality sweep costs almost nothing in PSNR and takes Canny's edge agreement from 0.949 to 0.895. Chroma subsampling saves 40% of the bytes for 0.09 of ΔE. And OpenCV and Pillow decode every JPEG here bit-for-bit identically — the disagreement is a 16-bit PNG, which Pillow silently opens as 8-bit.