regionprops() of imcomplement() of the image, requesting 'SubarrayIdx', and use those to access the image.
Note: you should also consider regionprops() of imcomplement() of the image, requesting 'Image' . You could use this if you are not interested in analyzing grayscale levels, just on/off
Note: if your image is binary, and your characters can have disconnected parts, then
regionprops(double(~BinaryImage), ...)
This prevents regionprops from considering each disconnected component separately.
Note: I am not familiar with the rules for Arabic, but in a number of other alphabets, the position of a character relative to the base-line can make a difference in the meaning of the character. For example in some languages a dot near the base-line is a period (punctuation) but a raised dot can indicate an accent or a vowel mark. Because of that, it is sometimes important to either not center the object, or else to also retain information about the object position for later testing against the base-line coordinates.
