In some texts that lossy preprosessing is called 'vector quantization'. The changes are lossy, they cannot be taken back after saving the image. Mathematical methods are developed to change image content cleverly before indexing to make a 255 colors palette possible to fit better. Unfortunately photos have gradients, 255 colors is often not enough. If the image has only 255 or less colors and the transparency is only full or none (=no partially transparent pixels) the result of course is perfect as is, you do not need any clever conversion methods. That depends on used dithering settings and how complex coloring the image has. indexing to 255 (+ full transparency) colors before saving as PNG gives nearly 75% size reduction, but the result looks out often pixelated or there's harmful banding. That's I came here to ask: How can I do the same within my gimp installation or by using the Linux command line tool imagemagick?įormat PNG8 ie. Have your cake and eat it too!Īs I find the service very important for running a website, I don't want to be dependent on them - they can disappear tomorrow, but I still have to minize pictures. The result better PNG files with 100% support for transparency. All unnecessary metadata is stripped too. By reducing the number of colors, 24-bit PNG files can be converted to much smaller 8-bit indexed color images.

When you upload a PNG (Portable Network Graphics) file, similar colors in your image are combined. On their website they write the following about how they do that: I recently discovered, which helped me to minimize a picture on my website from over 60k to less than 20k by keeping the same quaility (for me personally at first sight, I'm not so into graphics so I can not tell you exactly - it's my subjective opinion).

Tinypng alternative