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Theory and Practice of Sprixels: Difference between revisions

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==Color quantization==
==Color quantization==
The Kitty protocol accepts arbitrary RGBA 32-bit words in the sRGB color space; our natural internal format is 24bpp RGB plus two bits of alpha, so that's great—our colorspaces match. Sixel is a palette-indexed format. Common sizes are 16-, 256-, and 1024-entry palettes (in XTerm, this is controlled with the <tt>numColorRegisters</tt> X resource). Palettes are independent unless the <tt>privateColorRegisters</tt> resource is enabled). A color quantization step is thus necessary (note that this these quantizations can be performed in perfect parallelism when split across multiple frames/images, but not necessarily within a single frame). There are five essential color quantization algorithms:
The Kitty protocol accepts arbitrary RGBA 32-bit words in the sRGB color space; our natural internal format is 24bpp RGB plus two bits of alpha, so that's great—our colorspaces match. Sixel is a palette-indexed format. Common sizes are 16-, 256-, and 1024-entry palettes (in XTerm, this is controlled with the <tt>numColorRegisters</tt> X resource). Palettes are independent unless the <tt>privateColorRegisters</tt> resource is explicitly set false). A color quantization step is thus necessary (note that this these quantizations can be performed in perfect parallelism when split across multiple frames/images, but not necessarily within a single frame). There are five essential color quantization algorithms:


[[File:Penrosetiling.png|thumb|200px|right|These images throw libsixel for a loop; <tt>img2sixel</tt> chugs along, and then generates no output.]]
[[File:Penrosetiling.png|thumb|200px|right|These images throw libsixel for a loop; <tt>img2sixel</tt> chugs along, and then generates no output.]]