I am aware that transparent pixels in an animated GIF frame are determined by a transparent color index, where we can set a pixel to be transparent by assigning it to the value of the transparent color index when the transparent color flag is set to 1.
However, I have no clue how to determine what is the transparent color index of an animated GIF frame and whether the transparent color flag is set, as well as how to determine which pixels in a frame are of this color. I have looked around tools such as ImageMagick, wand, and Pillow, but I am not able to formulate a solution to find the number of transparent pixels.
Some pseudocode (in Python style) I have in mind to formulate my solution:
def count_transparent(frame):
count = 0
if transparent_flag(frame):
transparent_pixel = find_transparent_pixel(frame)
for row in frame:
for col in frame:
# Compare the colors
if frame[row][col] == transparent_pixel:
count += 1
return count
What tools/methods can I use (and how can I use them) to obtain information to find information pertaining to the transparent color flag and the transparent pixel for each animated GIF frame, where I am also allowed to iterate over each position of a frame?
The closest I have found is gifsicle, which appears to allow me to find information about the transparent color flag and the transparent pixel, but I am unable to iterate over each position of a frame with it. I appreciate something that I can use with Python, though a solution of any language is also welcome.
In ImageMagick, you can determine the number of transparent pixels by extracting the alpha channel, negate it so transparent is white and then getting the average (in range 0 to 1) of that image multiplied by width*height. For the 10th frame (starting at 0)
convert image.gif[9] -alpha extract -negate -format "%[fx:mean*w*h]" info:
should give you the number of transparent pixels.