grayscale image average without matlab function

Hi

I want to calculate the average of 3x3 cells of a matrix that contains the values of a grayscale image, which is a variable type is unit8

But for example, 2 cells have a value of 200, the sum of 2 of which is 400, but due to the Limitations of unit8 255 is calculated.

when use

pic=im2unit16(pic)

or

pic=unit16(pic)

then use imshow the result is a blank page

Thank you for your help

Answer 1

[Ameer Hamza]

First convert to uint16 (or double. Average the values and convert back to uint8

img = imread('pears.png');
r = img(:,:,1);
g = img(:,:,1);
b = img(:,:,1);

r = uint16(r);
g = uint16(g);
b = uint16(b);
img_gray = (r+g+b)/3;
imshow(uint8(img_gray))