Finding x,y coordinates of pixel by RGB color value

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awezmm
awezmm 2017-5-5
评论： Image Analyst 2018-1-23
Hi, Is there a reverse impixel function? I want to find the x and y coordinates of pixels in a color image by searching for them only with a RGB color value. I have tried converting into a binary image and searching for the '1' values by using
BW = im2bw(RGB, level)
and then [rows,cols] = find(BW==1);
but I am confused on how to set a level to implement an RGB value so that only my specific color pixels will show up as white in the binary image.
Is there a better way to find the coordinates of pixels only by using RGB value?
thanks!

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Image Analyst
Image Analyst 2017-5-5
Try this:
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Find where each color plane is your exact desired color value.
mask = redChannel == desiredRedValue && ...
greenChannel == desiredGreenValue & ...
blueChannel == desiredBlueChannel;
[rows, columns] = find(mask); % Note [rows, columns] = [y, x], NOT [x, y]
WHY do you want to do this. You probably don't need to and there is a better way if I just knew what you were going to do after this.
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awezmm
awezmm 2017-5-6
Thank you for your response. I've only been doing image processing for about the past 40 Minutes so I too have just barely scratched the surface. I am trying to catch ahead though.
My previous inquiry was too confusing. I was looking for a false range mask for rows and a completely DIFFERENT false range mask for columns. For instance if i only wanted to search in X coordinates of 10-20 and Y coordinates of 90-100? Is there a way to syntax a DIFFERENT false ranges for columns and rows.
Eventually I will be finding the distance between coordinates. And, yes I have gone through your demos. However, I believe this is the best way to go forward because I figured out that the desiredColor value can be a range in each channel and thus I can be easily searching for many different RGB values at the same time.
Image Analyst
Image Analyst 2017-5-6
I don't know what a "false range" is.
If you want to know what coordinates have x between 10 and 20 and y between 90 and 100, then do
indexes = columns >= 10 & columns <= 20 & rows >= 90 & rows <= 100;
% Extract only those in the range
c2 = columns(indexes);
r2 = rows(indexes);

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更多回答（1 个）

Franklin Prashanth C
编辑：Image Analyst 2018-1-23
How can I get these xy coordinate values, so that I can use it.?
[rows, cols] = find(BW==1); or
[rows, columns] = find(mask);
  1 个评论
Image Analyst
Image Analyst 2018-1-23
It just depends on whether you want the columns called "col" or "columns" and whether your binary image is called BW or mask. The ==1 is not necessary and can get deleted.

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