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How to know the real row and column indices of a pixel in the image

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Salad Box
Salad Box on 23 Oct 2019
Commented: Salad Box on 23 Oct 2019
Hi,
I have an image. See below.
>> fn = 'Unknown.jpg';
>> RGB = imread(fn);
>> whos RGB
Name Size Bytes Class Attributes
RGB 235x214x3 150870 uint8
>> s = size(RGB);
>> RGB = reshape(RGB, s(1)*s(2),3);
>> whos RGB
Name Size Bytes Class Attributes
RGB 50290x3 150870 uint8
After 'reshape', now 'RGB' becomes 50290 by 3.
I wonder that given a row index such as 37987 in the current form of RGB, how to find the corresponding pixel in the image and eventually draw a circle around that pixel on the image.
The main thing is to find the correspoinding pixel in the image.
I tried. However, the pixel I found is outside that image and is white as [255 255 255] which doesn't seems right at all.

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Answers (1)

Walter Roberson
Walter Roberson on 23 Oct 2019
which_pixel = 37987;
[r, c] = ind2sub([s(1), s(2)], which_pixel);
And remember that row corresponds to Y and column corresponds to X.

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Salad Box
Salad Box on 23 Oct 2019
Fabulous!!!!
It worked perfectly!!! You saved my day!!! Thanks a million!!!

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