How to change the pixel value of rgb unit8 image to NaN or black
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I have a rgb image, I want to change the pixel values greater than (r:175,g:255,b:55) to Nan or black . How can I do that. Please let me know Image info: I , uint8 0 255
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Accepted Answer
Image Analyst
on 22 May 2013
% See where all channels exceed (175, 255, 55) and
% set image to black for those pixels. (untested)
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Threshold each at the particular color
binaryRed = redChannel > 175;
binaryGreen = greenChannel > 255;
binaryBlue = blueChannel > 55;
% Find where all exceed threshold.
mask = binaryRed & binaryGreen & binaryBlue;
% Mask image to be black there.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask,class(rgbImage)));
imshow(maskedRgbImage);
More Answers (2)
Alex Taylor
on 22 May 2013
I think we would need some clarifying information to answer this question.
What does it mean to have a pixel value "greater" than (175,255,55)? If any one of the three channels is greater than your cutoff, do you want to clip to black? If all three channels are greater than your cutoff, do you want to clip to black?
Also, integer types do not define NaN, so you are going to need to use an integral value to represent black (e.g. 0).
Have you considered converting your image to grayscale before thresholding the intensity values? Have you considered thresholding in a different colorspace (working on the L channel in LAB space) then converting back?
2 Comments
Image Analyst
on 22 May 2013
Alex is right. We need the big picture here. WHY do you think you need to do that? What do you really want to do? It's possible that setting pixels to nan or black is not really the best approach to what you want to accomplish. So please share what you want to accomplish instead of focusing on what you think may be the best approach. Do you want to measure something (e.g. area, shape, or mean color) of objects of a particular color, or something else? You can upload your picture to http://snag.gy and tell us what you want to do or measure in your picture.
9 Comments
Image Analyst
on 22 May 2013
I'm 99% certain you don't need to convert anything to nan or black. What do you think you'd do if that were done?
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