# how compute the pixel sum for image?

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houssem rouine le 11 Avr 2018
Commenté : Walter Roberson le 28 Oct 2019
Hello freinds, I am a beginner in matlab and i want know how compute the pixel sum for image
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What is wrong with
doc sum
?! Even as a beginner it is surely the most obvious place to look.
You do need to collapse the image to 1d though or use a double sum, e.g.
pixelSum = sum( myImage(:) );
houssem rouine le 11 Avr 2018
thank you so much for your helping.

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### Réponses (1)

Pawel Jastrzebski le 11 Avr 2018
1. Use imread - output to load the image into Matlab and store it as a matrix - it can be anything between 2d and 4D matrix
2. Dimension 1 and 2 of the matrix are width and height of the image in pixels
% load the image into the matrix
dims = size(A)
NoOfPixels = prod(dims)
% Note if 'dims' is bigger than 2 elements then:
% NoOfPixels = prod(dims(1:2))
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Fhynthiazien Bobby le 28 Oct 2019
Hi, i tried using the code and my output is as below:
dims =
531 614 3
NoOfPixels =
978102
Therefore sir, does the value 978102 represents the overall sum of pixel for the image??
Walter Roberson le 28 Oct 2019
No, in that code, NoOfPixels is the number of array elements in the image. It is not necessarily the number of pixels: the number of pixels would be dims(1)*dims(2) . The difference comes about for RGB, in which there are 3 array elements per pixel.
If you are looking for the sum of the pixels, you need to define what that means for RGB.
sum(A, [1 2]) %since R2019a

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