# What would be the outcome of this line?

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Stelios Fanourakis on 25 Feb 2019
Commented: Rik on 25 Feb 2019
Hi
If I use this line code
for col = col1 : col2
row2 = find(mask(:, col), 1, 'last'); % Get bottom row of mask
heights(col) = row2 - topRow;
end
The heights will be a number of pixel intensity (e.g. pixel intensity value of X - pixel intensity value of Y) OR will be a number of pixels (e.g. 320 - 310 pixels = 10 pixels)??
Thank you

Stelios Fanourakis on 25 Feb 2019
Ok, now I know that the above line gives an arithmetic value, like 320-310 = 10 pixels.
But why when I use the line
heights(col) = rgbImage(320,col) - rgbImage(340,col);
I get the difference of pixel intensity values of those two pixels on the image? What's the difference between those two lines?
For instance if the pixel at position X: 320 Y: 454 has value of RGB: 88
And the pixel at position X: 340 Y: 454 has value RGB: 90
I will get result 2.
Why should I get result of 2 and NOT 20 which is the number of pixels between the two points?
Can someone explain clearly the difference?
Rik on 25 Feb 2019
You are subtracting positions to get a distance, you are subtracting values to get an intensity difference.
Since in this line
heights(col) = rgbImage(320,col) - rgbImage(340,col);
you're doing the second, it stands to reason you get an intensity difference, not a distance.