Legacy ImageMagick Discussions Archive

Update: A peer of mine directed me to this page: E-Dither Pixel Speckling . It describes how dithering "can produce the occasional odd-colored pixels in areas which would otherwise be fairly uniform in color". I believe this is the cause of my speckles. Since this is known and documented behavior, I ...

-colors 256 +dither If you want "+dither" to affect the processing of "-colors 256", put it before, not after. Thanks for the tip. If I do `+dither -colors 256`, the speckles go away... ... But I still think this is a bug if I just do `magick convert input.png -colors 256 output.png` and permit ...

Your one image probably has more than 256 colors to start. Correct. It has 259 colors. When you specify -colors 256 it forces some colors to change. That is what you are likely seeing. I certainly expect some colors to change, but I expect all instances of that color to change to another color. But ...

you probably end up with slightly different colors, such that two images do not have the same colormap. But the problem still occurs if I'm using only one image. Sorry if that wasn't clear from my previous message. (But even if I wasn't, isn't the 256 color limitation per-frame anyway? Wikipedia ...

Try this command: magick -delay 50 img_*.png -alpha on -layers optimize output.gif Ok, that works on my green squares test case. No change on my checkerboard test case, though - still the same artifacts as before. I now believe that the artifacts from the two test cases have different causes: the ...

The issue with the image pair I tested was solved simply by -colorspace gray -depth 8. If you're suggesting that as a general-purpose workaround, I don't know if I'd go as far as calling it a "solution", because I don't want my output to be grayscale. (To be clear, the sky in the checkerboard ...

So you're saying that the `-layers optimize` flag enforces gif color limitations even though the output isn't a gif? Ok, that seems reasonable. But even so, the sample input from my first post only has three unique colors, so the "artifacts appear due to colormap reduction" theory doesn't seem like ...

Thanks for your reply. I considered the possibility that "gifs can't have as many unique colors as pngs" might be the cause of the problem, but even if I execute the command: "C:\Program Files\ImageMagick-7.0.4-Q16\magick.exe" convert -delay 50 img_*.png -layers optimize output.png ... There are ...

I apologize for my late reply. I've installed the most recent release and I am still getting the same incorrect output as before. Version: ImageMagick 7.0.4-2 Q16 x64 2017-01-02 OS: Windows 10 Pro I have confirmed that I am not accidentally using an old version of ImageMagick, as I am explicitly ...

Including the `-alpha on` option as you suggest, does cause correct output to be produced. Thank you for suggesting this workaround. As to whether this behavior is something "actually broken" or simply just IM working as intended but in a surprising way, I'm still inclined to think that it truly is ...

ImageMagick version: 7.0.3-9 Q16 x64 2016-12-05, installed about an hour ago using ImageMagick-7.0.3-9-Q16-x64-dll.exe. Also reproducible with: ImageMagick 7.0.2-0 Q16 x64 2016-06-12 OS: Windows 10 Pro And Windows 7 Home Premium Steps to reproduce: 1) download the two .png images at http://imgur.com ...