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I'm trying to use Magick.NET to save palettized images generated by my program. Currently I'm using the following process:

  1. Create the image with MagickImage img = new(MagickColors.Green, (uint)Width, (uint)Height);
  2. Set img.ColorType = ColorType.Palette; and img.ColormapSize = 256;. Note that for the purpose of my issue (slow), it does not matter if step 2 is merged into the construction step 1.
  3. Copy the pixel data from my buffer to the image with SetByteArea, passing 4 identical bytes of the palette index for each pixel (so I don't have to care which byte is used to store the palette index).
  4. Set up the palette with SetColormapColor

This works, but step 2 (specifically setting ColorType is EXTREMELY slow; for the image I'm working with (8192x7680) it takes 18 seconds. Step 1 is also slower than I'd expect, taking about 2 seconds. How can I drastically speed up this process?

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  • Manually constructing a TGA file in a buffer (almost instantaneous) then passing it to the MagickImage constructor reduces the construction time to about 2 sec; not great, but tolerable. However this really isn't an answer to the question as the entire point of using Magick.NET was so that I wouldn't need to write any file format code... Commented Apr 16 at 6:42
  • Avoid ColorType.Palette Set the image to palettized mode during creation or use a direct pixel-writing method that assumes an indexed format. Write 1 byte per pixel (palette index) instead of 4, using a method designed for indexed images. Define the colormap in a single operation or during initialization. Use Magick.NET’s pixel cache or direct buffer manipulation to reduce copying. Use MagickFormat.Png8 to ensure the image is treated as 8-bit indexed from the start. Commented Apr 16 at 9:36
  • @SzymonRoziewski ...how do I do any of that? I tried doing MagickImage img = new(MagickColors.Green, (uint)Width, (uint)Height) { ColorType = ColorType.Palette, ColormapSize = 256 }; but this was not any faster than doing it in separate steps. Commented Apr 16 at 21:20
  • Can you post here a working example? Commented Apr 17 at 10:06
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