I = imread ("spritesheet.png");
for i = 1:rows(I)
  for j = 1:columns(I)
    if I(i,j,1) == 0 && I(i,j,2) == 136 && I(i,j,3) == 255
      I(i,j,:) = 0;
    endif
  endfor
endfor
imwrite(I,"spritesheet_w_background.png");