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How does one get a certain number of DominantColors and is it always possible to do so? I have tried specifying the number as well as the option ColorCoverage -> 0.

Example:

example of DominantColors output

More examples: 1, 2, 3

J. M.'s missing motivation
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Alderson
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    DominantColors[img, no. of colors]. Your problem may not be so trivial. In that case give an example where you think it is not working. – Sumit Jan 11 '17 at 17:59
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    @Sumit, I added an example. – Alderson Jan 11 '17 at 18:14
  • It's not possible using just options, it may return fewer than the requested number of colors. – M.R. Jan 11 '17 at 21:15
  • maybe request a few more than you need and take the top n. DominantColors[img,8, {"Color", "Count"}] It would be better if your uploaded example was just the image, not a screenshot with the white around it..BTW. – george2079 Jan 11 '17 at 22:34
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    FWIW I can not reproduce any case where DominantColors returns less than the requested number. (unless starting with an image with fewer discrete colors) @E.Alderson what version do you have? Can you see if you have this issue with some standard example, eg ExampleData[{"TestImage", "Splash"}] – george2079 Jan 11 '17 at 23:07
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    @george2079, Mathematica 11.0.1. The issue mostly occurs when working with monochromatic images (I added more examples). It works fine on Example Data. – Alderson Jan 12 '17 at 10:30
  • no issues with the new examples either ( v10.1 ). Even If I make a truely monochromatic image img=ImageMultiply[ColorConvert[ExampleData[{"TestImage", "Splash"}], "Grayscale"], Red] it works fine. – george2079 Jan 12 '17 at 15:43
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    Have you seen this? – J. M.'s missing motivation Jan 12 '17 at 17:32

1 Answers1

1

This seems to work in every case I've tried (v. 10.4, Mac).

ColorQuantize forces the number of colors in the image. Here's a screenshot of the original:

enter image description here

Here's the quantized image:

quantizedImage = ColorQuantize[img, 5]

enter image description here

My code worked fine on the screen shot of the poser's image, though admittedly the colors are rather dark.

Here are the extracted colors:

DominantColors[quantizedImage, 5]

{RGBColor[0.242519, 0.347167, 0.144226], 
 RGBColor[0.233793, 0.319928, 0.134609], 
 RGBColor[0.357113, 0.483923, 0.216957], 
 RGBColor[0.340756, 0.432562, 0.162432], 
 RGBColor[0.16798, 0.278479, 0.11706]}

or

Graphics[
 Table[{SortBy[DominantColors[quantizedImage, 5],Mean][[i]], 
        Disk[{2 i, 0}]}, 
      {i, 5}]]

enter image description here

I believe the dark colors arise because most of the image is quite dark, and the light highlights, while centered, represent a very small portion of the total image.

David G. Stork
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    I tried to grab the OP's image, had to do a screencapture for it, but here it is. But I couldn't get it to work with your code – Jason B. Jan 11 '17 at 20:01
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    @user9490, didn't work for me too, I got only two colors. – Alderson Jan 11 '17 at 20:02
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    This does give the five colors from the quantized image, they are a bit darker than the dominant colors found by the built-in function: RGBColor@*Most /@ Union[Flatten[ImageData[quantizedImage], 1]] – Jason B. Jan 11 '17 at 20:06
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    I have been using this function for color extraction, even though it does not produce the desired output:color[img_] := MapAt[RGBColor, Tally[Flatten[ImageData[ColorQuantize[ImageResize[img, 50], 5]], 1]], {All, 1}] col[img_] := First[#] & /@ color[img]; – Alderson Jan 11 '17 at 20:10
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    @David didn't work for me either – M.R. Jan 11 '17 at 21:04