Edit an indexed PNG palette

An indexed PNG does not store red, green and blue at every position. It stores a small integer and a PLTE table that says which colour each integer means. Changing one table entry recolours every pixel carrying that index without rendering the image into a new grid.

The workbench probes the file header and reports the entry count. When palette output is available, the exported file copies the compressed pixel data and replaces only the selected RGB triplet in PLTE, then recomputes that chunk's CRC.

The Palette panel shows the table itself as a grid: every entry numbered as the file stores it, with the share of pixels that point at it, read from the inflated index rows. Choose an entry to set its value directly, and let its family — nearby entries an antialiased edge is made of — move with it. After saving, the page compares the two files and prints the proof: size unchanged, every byte outside PLTE identical, the PLTE checksum verified.

1. It applies only to colour-type-3 indexed PNG, not to true-colour PNG, JPEG, WebP or a file merely named .png.
2. One visible object can use several entries for antialiasing and shading, so changing a single swatch may leave a fringe.
3. Two objects sharing the same entry cannot be separated without changing pixel indices, which this lossless path deliberately refuses to do.

• Change a logo's colourFlat-art selection by one ΔE radius, exact hex replacement and the indexed-PNG table path.
• Map onto a paletteMove every pixel to its nearest of your 2–16 swatches, with usage per swatch.
• Indexed PNG palettesAt most 768 bytes rewritten, one CRC recomputed, and no pixel index touched.
• Replace a colourThe dropper armed on open, two swatches, one operation and nothing else to manage.