P vs. L Mode in PIL: When to Use Palettized or Luminance Images?

Differences between P and L Mode in PIL

PIL's P mode (palettised) and L mode (luminance) offer distinct advantages and disadvantages when working with images.

P Mode (Palettised)

• Stores each pixel as an index into a palette with up to 256 colors.
• Less storage space required compared to RGB (1/3 of the size).
• Limited to 256 unique colors, potentially resulting in banding or artefacts.

L Mode (Luminance)

• Single-channel image representing only the luminance (brightness), interpreted as grayscale.
• Compact storage but represents only grayscale, not color.

Conversion Between Modes

You can convert between modes using the convert(mode) function:

# Convert to RGB mode
image.convert('RGB')

# Convert to P mode
image.convert('P')

# Convert to L mode
image.convert('L')

Example Images

• P Mode: A GIF file or a greyscale image with limited shades.
• L Mode: A black-and-white photo or a greyscale image with smooth transitions.

Notes

• Images can be stored in RGB even when appearing grayscale by setting R, G, and B components equal.
• Greyscale images can be stored in P mode by ensuring all palette entries have R, G, and B values equal.

Best Practices

To avoid potential issues, convert images to RGB on opening:

im = Image.open("image.jpg").convert('RGB')

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