Replacing RGB value for image segmentation

Question

Bruno Fcav 2019-3-20

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https://ww2.mathworks.cn/matlabcentral/answers/451076-replacing-rgb-value-for-image-segmentation

评论： Image Analyst 2019-3-21

Hi!

Is it possible, for certain RGB values of pixels in an image, to make modifications like this below?

For example, for pixels with values in ranges: Red between 170 - 120, Green 150 - 120 and Blue between 70 - 50, I would not like to modify. But for pixels that are not in this range, I'd like to make them in black color.

Thanks.

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Answer 1

Image Analyst 2019-3-20

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Sure. Just make a mask and apply it:

rgbImage = imread('peppers.png');
subplot(2, 1, 1);
imshow(rgbImage);
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Create a mask for each channel and use it to zero out the image.
mask = ~(redChannel >= 120 & redChannel <= 170);
redChannel(mask) = 0;
mask = ~(greenChannel >= 120 & greenChannel <= 150);
greenChannel(mask) = 0;
mask = ~(blueChannel >= 50 & blueChannel <= 70);
blueChannel(mask) = 0;
% Recombine separate color channels into a single, true color RGB image.
rgbImage2 = cat(3, redChannel, greenChannel, blueChannel);
subplot(2, 1, 2);
imshow(rgbImage2);

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Bruno Fcav 2019-3-20

EsmeraldaCut.png

It did not work very well for what I need, but it must have been my mistake. I'd like to segment only the light green parts of the figure. For this I studied some color trends for the areas of interest and arrived at the ranges of values that I proposed in my question. I'll try to change the methodology ...

Image Analyst 2019-3-21

testRGBImage.m

It was a mistake to try to segment this in RGB color space. You need to use a colorimetric color space like HSV. I used the Color Thresholder app on the Apps tab of the tool ribbon to determine thresholds to use in HSV color space. Try the attached demo.