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JPEG compression

sophielwang.com · 153 words · saved by 1 readers

JPEG is a clever image compression algorithm that makes a change of basis before encoding. The rewritten image representation concentrates the signal that humans are most perceptive to, so that the remaining details can be discarded without horribly degrading visual fidelity. A digital image is a mapping from two-dimensional spatial coordinates to pixel values: 𝐼 : 𝐷 ⊂ 𝑍 2 → 𝐶 . I:D⊂Z 2 →C. Here 𝐷 D is a finite grid of pixel locations and 𝐶 C is the set of possible values. In the 𝑅 𝐺 𝐵 RGB model, 𝐶 = { 0 , … , 255 } 3 C={0,…,255} 3 , representing three 8-bit color channels. A property of human vision is that we are more sensitive to luminance (brightness) than to chrominance (color differences). Edges and fine detail in brightness are noticeable, while small variations in color are much harder to perceive. JPEG exploits this by separating brightness from color, meaning that instead of working directly in 𝑅 𝐺 𝐵 RGB, each pixel is converted to the Y'CbCr color space: (

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