Depends on your definition of area of the painting. Is every point with colour anything but absolute white considered as a part of the painting? Assuming that anything brighter than the mid level of gray to be an unpainted region, the following code must be able to get the area of a painting:
Im = imread('File location');
ImBW = Im(:,:,2);
imshow(ImBW);
threshold = 127;
area = 0;
for i = 1 : length(ImBW(:,1))
for j = 1 : length(ImBW(1,:))
if(ImBW(i,j)>threshold)
area = area+1;
end
end
end
Use this to compute the areas of the different images and take difference accordingly.
Hope it helps.
