gif writer with pillow

gif-writer.py

"""Write a gif where a line moves horizontally.

Note that this code does not work with pillow 3.4.0
(only the first frame is written).
Tested with pillow 5.0.0.

"""

from PIL import Image


if __name__ == "__main__":
    SIZE = 100
    images = []

    # write the gif
    for offset in range(SIZE):
        img = Image.new('L', (SIZE, SIZE), 0)
        pixmap = img.load()
        for row in range(SIZE):
            pixmap[offset, row] = 255
        images.append(img)
    first, *lasts = images
    assert lasts, "only one frame in gif"
    first.save('progress-bar.gif', save_all=True, append_images=images, duration=10)


    # count number of frames
    gif = Image.open('progress-bar.gif')
    nb_frame = 1
    try:
        while True:
            gif.seek(gif.tell()+1)
            nb_frame += 1
    except EOFError:
        pass
    assert nb_frame == SIZE, 'nb frame: ' + str(nb_frame)


def basic_use():
    import random
    from PIL import ImageDraw
    img = Image.new('RGB', (400, 400), (255, 255, 255))
    draw = ImageDraw.Draw(img)
    draw.line((0, 5, 10, 5), (0, 0, 0), 2)
    draw.line((5, 0, 5, 10), (0, 0, 0), 2)
    img.save("test-bad-lines.png", 'PNG')

    rand = lambda: random.randint(0, 255)
    rand_color = lambda: (rand(), rand(), rand())
    pixmap = img.load()
    for i in range(400):
        for j in range(400):
            pixmap[i, j] = rand_color()
    img.save("test-random.png", 'PNG')