DIY Java CMYK-to-RGB Conversion Beats Built-in ColorConvertOp by 6x

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A Java developer investigating a slow image-decoding bottleneck found that manually converting CMYK pixel data to RGB was dramatically faster than using Java's built-in ColorConvertOp filter. The custom approach processed a sample page in just 11 seconds on a Mac, compared to 73 seconds with the standard ColorConvertOp method. A key optimisation in the manual version caches the last converted pixel value, avoiding redundant calculations for repeated colours — particularly beneficial for large areas of uniform colour. The developer has retained the original code in hopes that Oracle will eventually optimise the filter function, but is currently using the faster DIY implementation.

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