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Given x and y coordinates of any point in an image, how to know if it is black or white

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Hasan
Hasan on 20 Mar 2014
Edited: Nitin on 21 Mar 2014
Given x and y coordinates of any point in an image, how to know if it is black or white?

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Answers (2)

Nitin
Nitin on 21 Mar 2014
Edited: Nitin on 21 Mar 2014
By the intensity value you get at that point.
For example, if your image is double:
I = im2double(imread('img.bmp'));
% Edited the mistake as suggested by ImageAnalyst
val = I(y,x);
if val is zero, then it is black.
if val is one, then it is white.
Have a look at a binary image and it will make sense.
I= imread('img.bmp');
bin_img=im2bw(I);
imshow(bin_img),colorbar

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Image Analyst
Image Analyst on 21 Mar 2014
If it's logical or single or double,
if theImage(y, x) == 0
% It's black.
else
% It's white.
end
Or, it if's uint8 instead of logical or double or single, if it's 0 it's black, if it's 255 it's white, and if it's in between it's a shade of gray.
Be careful of the common mistake Nitin made where he said I(x, y). The row (y) is the first index and the column (x) is the second coordinate, so if you want the value at some x,y coordinate, it would be I(y, x).

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