How to Extract Frame From GIF, and Reconstruct the Details of each Frame?

Question

I try to extract each frame from GIF file.

I found two ways to deal with this problem.

1 Find an online tool to solve it.

https://ezgif.com/split

It is an excellent tool. It can redraw the details. Frames extracted from the GIF are in high quality.

2 Try to use python library to solve this problem.

I use PIL, but it comes with a knotty problem. The frame extracted lost many details with white edges.

So I want to ask what is the algorithm EZGif take, and how to implement it with python?

Answer 1

Got a useful reference of your problem.

import os
from PIL import Image


'''
I searched high and low for solutions to the "extract animated GIF frames in Python"
problem, and after much trial and error came up with the following solution based
on several partial examples around the web (mostly Stack Overflow).
There are two pitfalls that aren't often mentioned when dealing with animated GIFs -
firstly that some files feature per-frame local palettes while some have one global
palette for all frames, and secondly that some GIFs replace the entire image with
each new frame ('full' mode in the code below), and some only update a specific
region ('partial').
This code deals with both those cases by examining the palette and redraw
instructions of each frame. In the latter case this requires a preliminary (usually
partial) iteration of the frames before processing, since the redraw mode needs to
be consistently applied across all frames. I found a couple of examples of
partial-mode GIFs containing the occasional full-frame redraw, which would result
in bad renders of those frames if the mode assessment was only done on a
single-frame basis.
Nov 2012
'''


def analyseImage(path):
    '''
    Pre-process pass over the image to determine the mode (full or additive).
    Necessary as assessing single frames isn't reliable. Need to know the mode 
    before processing all frames.
    '''
    im = Image.open(path)
    results = {
        'size': im.size,
        'mode': 'full',
    }
    try:
        while True:
            if im.tile:
                tile = im.tile[0]
                update_region = tile[1]
                update_region_dimensions = update_region[2:]
                if update_region_dimensions != im.size:
                    results['mode'] = 'partial'
                    break
            im.seek(im.tell() + 1)
    except EOFError:
        pass
    return results


def processImage(path):
    '''
    Iterate the GIF, extracting each frame.
    '''
    mode = analyseImage(path)['mode']

    im = Image.open(path)

    i = 0
    p = im.getpalette()
    last_frame = im.convert('RGBA')

    try:
        while True:
            print "saving %s (%s) frame %d, %s %s" % (path, mode, i, im.size, im.tile)

            '''
            If the GIF uses local colour tables, each frame will have its own palette.
            If not, we need to apply the global palette to the new frame.
            '''
            if not im.getpalette():
                im.putpalette(p)

            new_frame = Image.new('RGBA', im.size)

            '''
            Is this file a "partial"-mode GIF where frames update a region of a different size to the entire image?
            If so, we need to construct the new frame by pasting it on top of the preceding frames.
            '''
            if mode == 'partial':
                new_frame.paste(last_frame)

            new_frame.paste(im, (0,0), im.convert('RGBA'))
            new_frame.save('%s-%d.png' % (''.join(os.path.basename(path).split('.')[:-1]), i), 'PNG')

            i += 1
            last_frame = new_frame
            im.seek(im.tell() + 1)
    except EOFError:
        pass


def main():
    processImage('foo.gif')
    processImage('bar.gif')


if __name__ == "__main__":
    main()

Answer 2

GIF transparency in PIL is broken. Not sure why it is that way, but it`sa fact.

You can try using my GIF library instead, for which I`ve just made a Python frontend:

from PIL import Image

def GIF_Load(file):
    from platform import system
    from ctypes import string_at, Structure, c_long as cl, c_ubyte, \
                       py_object, pointer, POINTER as PT, CFUNCTYPE, CDLL
    class GIF_WHDR(Structure): _fields_ = \
       [("xdim", cl), ("ydim", cl), ("clrs", cl), ("bkgd", cl),
        ("tran", cl), ("intr", cl), ("mode", cl), ("frxd", cl), ("fryd", cl),
        ("frxo", cl), ("fryo", cl), ("time", cl), ("ifrm", cl), ("nfrm", cl),
        ("bptr", PT(c_ubyte)), ("cpal", PT(c_ubyte))]
    def intr(y, x, w, base, tran): base.paste(tran.crop((0, y, x, y + 1)), w)
    def skew(i, r): return r >> ((7 - (i & 2)) >> (1 + (i & 1)))
    def WriteFunc(d, w):
        cpal = string_at(w[0].cpal, w[0].clrs * 3)
        list = d.contents.value
        if (len(list) == 0):
            list.append(Image.new("RGBA", (w[0].xdim, w[0].ydim)))
        tail = len(list) - 1
        base = Image.frombytes("L", (w[0].frxd, w[0].fryd),
                               string_at(w[0].bptr, w[0].frxd * w[0].fryd))
        if (w[0].intr != 0):
            tran = base.copy()
            [intr(skew(y, y) + (skew(y, w[0].fryd - 1) + 1, 0)[(y & 7) == 0],
                  w[0].frxd, (0, y), base, tran) for y in range(w[0].fryd)]
        tran = Image.eval(base, lambda indx: (255, 0)[indx == w[0].tran])
        base.putpalette(cpal)
        list[tail].paste(base, (w[0].frxo, w[0].fryo), tran)
        list[tail].info = {"delay" : w[0].time}
        if (w[0].ifrm != (w[0].nfrm - 1)):
            list.append(list[max(0, tail - int(w[0].mode == 3))].copy())
            if (w[0].mode == 2):
                base = Image.new("L", (w[0].frxd, w[0].fryd), w[0].bkgd)
                base.putpalette(cpal)
                list[tail + 1].paste(base, (w[0].frxo, w[0].fryo))
    try: file = open(file, "rb")
    except IOError: return []
    file.seek(0, 2)
    size = file.tell()
    file.seek(0, 0)
    list = []
    CDLL(("%s.so", "%s.dll")[system() == "Windows"] % "gif_load"). \
    GIF_Load(file.read(), size,
             CFUNCTYPE(None, PT(py_object), PT(GIF_WHDR))(WriteFunc),
             None, pointer(py_object(list)), 0)
    file.close()
    return list

def GIF_Save(file, fext):
    list = GIF_Load("%s.gif" % file)
    [pict.save("%s_f%d.%s" % (file, indx, fext))
     for (indx, pict) in enumerate(list)]

GIF_Save("insert_gif_name_here_without_extension", "png")