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Better sRGB to greyscale conversion

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Better sRGB to greyscale conversion is an October 2025 technical blog post on 30fps.net about converting gamma-encoded sRGB to greyscale without misusing Rec. 709 weights in gamma space.

It covers why weighting R-prime, G-prime, and B-prime with Rec. 709 coefficients mixes luma and luminance, the linearize-then-Y-then-encode pipeline, alternative gamma-space weights from Poynton via image-processing books, Asahi Lina coefficients for saturated primaries, photo comparisons against linear sRGB and CIELAB L-star, and notes on Photoshop Rec. 601 practice.

It is for graphics and shader programmers who sample sRGB textures and need a clearer luma-versus-luminance model. Some color-management vocabulary helps, though beginners can still follow the three-step correct path.

The post is a free web article with formulas, comparison images, error maps, and a short footnote to related HDR display material.

It is useful when greyscale paths look slightly wrong on saturated colors and you must choose between true linear luminance and approximate gamma-space luma weights.