How can I set up an RGB threshold

Question

Feynman 2013-11-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/104920-how-can-i-set-up-an-rgb-threshold

评论： Image Analyst 2014-3-27

I am given an image and using an input value by the user called thrper I am to calculate a threshold value for each of the color layers I have made

[image_R, image_G, image_B] = seperate_RGB_components(image_RGB)
I am to only use explicit loops such as for,if and else. In his example my professor sets thrper to .75 meaning the bottom 75% values will be converted to black and the top 25% will be converted to white (0 and 255 respectively). Will I need to use a combination of for and if loops to do so? Or is there a simpler method using only one of the explicit loops?

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Answer 1

David Sanchez 2013-11-5

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/104920-how-can-i-set-up-an-rgb-threshold#answer_114177

在 MATLAB Online 中打开

There are easy ways to do this, but if you MUST use for loops and if conditionals:

[image_R, image_G, image_B] = seperate_RGB_components(image_RGB)
thrper = .75 % threshold
% separate the layers
image_R = image(:,:,1);
R_thres = sum(sum(image_R))/numel(image_R);
image_G = image(:,:,2);
G_thres = sum(sum(image_G))/numel(image_G);
image_B = image(:,:,3);
B_thres = sum(sum(image_B))/numel(image_B);
% apply filter
[rows cols] = size( image_R ); % number of rows and columns
% RED LAYER
for k_r = 1:rows
for k_c = 1:cols
  if (image_R(k_c,k_r) < R_thres)
      image_R(k_c,k_r) = 0;
  else
      image_R(k_c,k_r) = 255;
  end
end
end
% GREEN LAYER
for k_r = 1:rows
for k_c = 1:cols
  if (image_G(k_c,k_r) < G_thres)
      image_G(k_c,k_r) = 0;
  else
      image_G(k_c,k_r) = 255;
  end
end
end
% BLUE LAYER
for k_r = 1:rows
for k_c = 1:cols
  if (image_B(k_c,k_r) < B_thres)
      image_B(k_c,k_r) = 0;
  else
      image_B(k_c,k_r) = 255;
  end
end
end

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Sabanam 2014-3-27

After getting individual Segmented image R,G,B,how can i show single segmented image or combine three results?

Image Analyst 2014-3-27

What would the single image represent? Do you want to AND or OR the three individual images together? We have no idea how you want to, or should, combine your 3 images. Why not start your own thread with your own image attached?

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Answer 2

Feynman 2013-11-5

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/104920-how-can-i-set-up-an-rgb-threshold#answer_114246

在 MATLAB Online 中打开

    image_R = image(:,:,1);
    R_thres = sum(sum(image_R))/numel(image_R);
    image_G = image(:,:,2);
    G_thres = sum(sum(image_G))/numel(image_G);
    image_B = image(:,:,3);
    B_thres = sum(sum(image_B))/numel(image_B);
This code won't calculate the range of the image RGB will it? The function should prompt the user to enter a percentage to be saved as thrper and by finding the range of values in the image layer find the points in which the pixel value should be reset to 0 or 255 so if the red layer had values ranging from -100 to 300 the threshold value should be 200 so any pixel below 200 will be set to 0 and any value above 200 will be set to 255