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In a picture, there are many different colors. How can I just want to find the position of one color. In the following picture, if I would like to find the coordinates of the position of blue, how can I achieve that? Thank you very much! enter image description here

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By Blue you mean RGBColor[0,0,1]? Is PixelValuePositions ok? –  Kuba Oct 31 '13 at 7:17
    
@Kuba I think that is a good answer. image = Import["1wEvU.jpg"]; PixelValuePositions[image, Blue, 0.4] gave me {{1605, 810}, {1606, 810}, {1604, 809}, {1605, 809}, ... –  Nasser Oct 31 '13 at 7:22
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1 Answer 1

up vote 13 down vote accepted
image = Import["http://i.stack.imgur.com/1wEvU.jpg"];

Look for anything within 0.3 of Blue:

pv = PixelValuePositions[image, Blue, .3]

{{1614, 784}}

Just one pixel is that close to pure Blue. To display it:

HighlightImage[image, pv, "HighlightColor" -> White, 
  Method -> {"DiskMarkers", 20}]

It's over by the Balloon(?).

image

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Ooh, I've never come across HighlightImage before. +1, but why is it community wiki? –  Simon Woods Oct 31 '13 at 10:35
    
@SimonWoods :) Too long to be yet another comment-as-answer, but didn't want to snatch credit away from commenters... –  cormullion Oct 31 '13 at 10:37
    
@cormullion Can PixelValuePositions be used to find some "strange" color? –  KathyLL Oct 31 '13 at 21:35
    
@kathyLL any color will work, if you know its RGB values. But strangeness needs defining! :) –  cormullion Oct 31 '13 at 21:51
    
@cormullion Thanks a lot! –  KathyLL Nov 1 '13 at 18:21
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