"Noise" in the background of GIF animations

[jiannmeng]

What did you do?

Saved an animated GIF with a plain background and an incrementing integer in the middle.

What did you expect to happen?

The output should look like this (the "good" gif):

What actually happened?

The output looks like this (the "bad" gif):

Notice the background is full of noise, and the noise at the bottom right changes every frame.

What are your OS, Python and Pillow versions?

• OS: Windows 10
• Python: 3.7
• Pillow: 6.2.1

from PIL import Image, ImageDraw, ImageFont
from io import BytesIO

save_kwargs = {
    "format": "GIF",
    "save_all": True,
    "duration": 100,
    "loop": False,
}

font = ImageFont.truetype(font="arial", size=36)
frames = []
for i in range(0, 20):
    frame = Image.new("RGB", (200, 200), color="#FFAD94")
    draw = ImageDraw.Draw(frame)
    draw.text((90, 90), str(i), font=font)
    frames.append(frame)

# Bad - Save the Image objects directly to an animated GIF.
frames[0].save("bad.gif", append_images=frames[1:], **save_kwargs)

# Good - Save each Image object as a static GIF, then stitch the GIFs together
# to form the animated GIF.
byteframes = []
for f in frames:
    byte = BytesIO()
    byteframes.append(byte)
    f.save(byte, format="GIF")
imgs = [Image.open(byteframe) for byteframe in byteframes]
imgs[0].save("good.gif", append_images=imgs[1:], **save_kwargs)

[radarhere]

By changing the mode of the image to P, I find that the following code works -

from PIL import Image, ImageDraw, ImageFont
from io import BytesIO

save_kwargs = {
    "format": "GIF",
    "save_all": True,
    "duration": 100,
    "loop": False,
}

font = ImageFont.truetype(font="/System/Library/Fonts/Supplemental/Arial.ttf", size=36)
frames = []
for i in range(0, 20):
    frame = Image.new("P", (200, 200), color="#FFAD94")
    draw = ImageDraw.Draw(frame)
    draw.text((90, 90), str(i), "#fff", font=font)
    frames.append(frame)

frames[0].save("bad.gif", append_images=frames[1:], **save_kwargs)

[jiannmeng]

Thanks @radarhere , changing "RGB" to "P" works perfectly - and was about 10x faster than "RGB" mode!

[radarhere]

Does that resolve this issue for you then?

[jiannmeng]

Yes, thank you!

[vikky1992]

If we are not creating the image by Image.new() method and we are reading an existing .png image, how can we set the mode parameter?

[radarhere]

To change an image from one mode to another, use the convert method - https://pillow.readthedocs.io/en/latest/reference/Image.html#PIL.Image.Image.convert