Confusing errors when saving zero-dimension images instead of clear validation #9389

What did you do?

Attempted to save an image with zero width or zero height.

from PIL import Image

img = Image.new('RGB', (0, 50))  # zero-width image
img.save('test.gif')
img.save('test.png')

What did you expect to happen?

A clear validation error like:

ValueError: Cannot save image with zero width or height (got size: (0, 50))

What actually happened?

GIF save:

ValueError: max() iterable argument is empty

(from GifImagePlugin.py line 959 in _get_optimize)

PNG save:

SystemError: tile cannot extend outside image

(from ImageFile.py line 682 in _encode_tile)

Context

I encountered this when using ImageGrab.grab(bbox=...) with programmatically-determined coordinates. When window detection returned invalid bounds (e.g., bbox=(50, 50, 50, 100) resulting in width=0), the save operation failed with these confusing errors.

from PIL import ImageGrab

frame = ImageGrab.grab(bbox=(50, 50, 50, 100))  # bad coords → width=0
print(frame.size)  # (0, 50)
frame.save('output.gif')  # confusing error

Note on existing issues

• Issue Image of size zero is not getting initialized #2259 intentionally allowed creating zero-dimension images (for mathematical operations like fold/reduce)
• Resizing to zero dimensions gives a clear error: height and width must be > 0
• But saving zero-dimension images was never given proper validation

Suggested fix

Add dimension validation at the start of Image.save():

if self.size[0] == 0 or self.size[1] == 0:
    raise ValueError(
        f"Cannot save image with zero width or height (got size: {self.size})"
    )

Environment

• Pillow version: 12.1.0
• Python version: 3.12.5
• Platform: Windows 11