A frame is *ignored* when a GIF is saved with a completely transparent frame included

[hsohliyt105]

What did you do?

I tried to save a gif file with a completely transparent frame.

What did you expect to happen?

What actually happened?

You can see that the last empty frame does not appear. Instead, the duration of the previous frame is delayed.

What are your OS, Python and Pillow versions?

• OS: I tried both Windows 10, MacOS, and Raspbian
• Python: 3.10.4
• Pillow: 9.3.0

Note that I came up with a simple code rather than my original code to keep this simple.

from PIL import Image, ImageDraw

image1 = Image.new("RGBA", (100, 100), "#00000000")
image2 = Image.new("RGBA", (100, 100), "#00000000")
image3 = Image.new("RGBA", (100, 100), "#00000000")

draw = ImageDraw.Draw(image2)
draw.rectangle((25, 25, 75, 75), fill = "#FF0000FF")

image1.save("example.gif", format="GIF", save_all=True, disposal=2, loop=0, duration=1000, append_images=[image2, image3])

This also happens when a completely black (#000000) image is appended, regardless of the transparency.

from PIL import Image, ImageDraw

image1 = Image.new("RGBA", (100, 100), "#00000000")
image2 = Image.new("RGBA", (100, 100), "#00000000")
image3 = Image.new("RGBA", (100, 100), "#00000000")

draw = ImageDraw.Draw(image2)
draw.rectangle((25, 25, 75, 75), fill = "#FF0000FF")

draw = ImageDraw.Draw(image3)
draw.rectangle((25, 25, 75, 75), fill = "#000000FF")

image1.save("example.gif", format="GIF", save_all=True, disposal=2, loop=0, duration=1000, append_images=[image2, image3])

*edit
I checked that "white" (#FFFFFF00) transparent images are normally appended to the image.

Example code:

from PIL import Image, ImageDraw

image1 = Image.new("RGBA", (100, 100), "#FFFFFF00")
image2 = Image.new("RGBA", (100, 100), "#FFFFFF00")
image3 = Image.new("RGBA", (100, 100), "#FFFFFF00")

draw = ImageDraw.Draw(image2)
draw.rectangle((25, 25, 75, 75), fill = "#FF0000FF")

image1.save("example.gif", format="GIF", save_all=True, disposal=2, loop=0, duration=1000, append_images=[image2, image3])

This will produce the wanted result. But anyways, I think this still is an issue.

[radarhere]

I've created PR #6787 to resolve this.