Overly large PA palette

[bryghtlabs-richard]

What did you do?

I converted an image->RGBA->PA and counted the palette colors.

What did you expect to happen?

I expected the palette to contain no more colors than the number of pixels in the image, or possibly no more than rounding up to the next power of two.

What actually happened?

The palette contains many more entries than pixels in the image.

What are your OS, Python and Pillow versions?

• OS: Windows 11
• Python: 3.13.3
• Pillow: 11.2.1

--------------------------------------------------------------------
Pillow 11.2.1
Python 3.13.3 (tags/v3.13.3:6280bb5, Apr  8 2025, 14:47:33) [MSC v.1943 64 bit (AMD64)]
--------------------------------------------------------------------
Python executable is C:\Python313\python.exe
System Python files loaded from C:\Python313
--------------------------------------------------------------------
Python Pillow modules loaded from C:\Users\RichardAllen\AppData\Roaming\Python\Python313\site-packages\PIL
Binary Pillow modules loaded from C:\Users\RichardAllen\AppData\Roaming\Python\Python313\site-packages\PIL
--------------------------------------------------------------------
--- PIL CORE support ok, compiled for 11.2.1
--- TKINTER support ok, loaded 8.6
--- FREETYPE2 support ok, loaded 2.13.3
--- LITTLECMS2 support ok, loaded 2.17
--- WEBP support ok, loaded 1.5.0
*** AVIF support not installed
--- JPEG support ok, compiled for libjpeg-turbo 3.1.0
--- OPENJPEG (JPEG2000) support ok, loaded 2.5.3
--- ZLIB (PNG/ZIP) support ok, loaded 1.3.1.zlib-ng, compiled for zlib-ng 2.2.4
--- LIBTIFF support ok, loaded 4.7.0
*** RAQM (Bidirectional Text) support not installed
*** LIBIMAGEQUANT (Quantization method) support not installed
*** XCB (X protocol) support not installed
--------------------------------------------------------------------

Input Image is 2x2 [[Black, Reddish], [Greenish, Blueish]] (it's not really blurry, there's really only 4 colors in the image, but if I don't zoom in with HTML, it's too small to see):

from PIL import Image
img = Image.open("rgb.png")
img = img.convert("RGBA")
img = img.convert("PA", palette=Image.ADAPTIVE, colors=4) # No difference removing palette and colors
print("Palette:", img.getpalette())
print("Data:", list(img.getdata()))

Palette: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 51, 0, 0, 102, 0, 0, 153, 0, 0, 204, 0, 0, 255, 0, 0, 0, 51, 0, 51, 51, 0, 102, 51, 0, 153, 51, 0, 204, 51, 0, 255, 51, 0, 0, 102, 0, 51, 102, 0, 102, 102, 0, 153, 102, 0, 204, 102, 0, 255, 102, 0, 0, 153, 0, 51, 153, 0, 102, 153, 0, 153, 153, 0, 204, 153, 0, 255, 153, 0, 0, 204, 0, 51, 204, 0, 102, 204, 0, 153, 204, 0, 204, 204, 0, 255, 204, 0, 0, 255, 0, 51, 255, 0, 102, 255, 0, 153, 255, 0, 204, 255, 0, 255, 255, 0, 0, 0, 51, 51, 0, 51, 102, 0, 51, 153, 0, 51, 204, 0, 51, 255, 0, 51, 0, 51, 51, 51, 51, 51, 102, 51, 51, 153, 51, 51, 204, 51, 51, 255, 51, 51, 0, 102, 51, 51, 102, 51, 102, 102, 51, 153, 102, 51, 204, 102, 51, 255, 102, 51, 0, 153, 51, 51, 153, 51, 102, 153, 51, 153, 153, 51, 204, 153, 51, 255, 153, 51, 0, 204, 51, 51, 204, 51, 102, 204, 51, 153, 204, 51, 204, 204, 51, 255, 204, 51, 0, 255, 51, 51, 255, 51, 102, 255, 51, 153, 255, 51, 204, 255, 51, 255, 255, 51, 0, 0, 102, 51, 0, 102, 102, 0, 102, 153, 0, 102, 204, 0, 102, 255, 0, 102, 0, 51, 102, 51, 51, 102, 102, 51, 102, 153, 51, 102, 204, 51, 102, 255, 51, 102, 0, 102, 102, 51, 102, 102, 102, 102, 102, 153, 102, 102, 204, 102, 102, 255, 102, 102, 0, 153, 102, 51, 153, 102, 102, 153, 102, 153, 153, 102, 204, 153, 102, 255, 153, 102, 0, 204, 102, 51, 204, 102, 102, 204, 102, 153, 204, 102, 204, 204, 102, 255, 204, 102, 0, 255, 102, 51, 255, 102, 102, 255, 102, 153, 255, 102, 204, 255, 102, 255, 255, 102, 0, 0, 153, 51, 0, 153, 102, 0, 153, 153, 0, 153, 204, 0, 153, 255, 0, 153, 0, 51, 153, 51, 51, 153, 102, 51, 153, 153, 51, 153, 204, 51, 153, 255, 51, 153, 0, 102, 153, 51, 102, 153, 102, 102, 153, 153, 102, 153, 204, 102, 153, 255, 102, 153, 0, 153, 153, 51, 153, 153, 102, 153, 153, 153, 153, 153, 204, 153, 153, 255, 153, 153, 0, 204, 153, 51, 204, 153, 102, 204, 153, 153, 204, 153, 204, 204, 153, 255, 204, 153, 0, 255, 153, 51, 255, 153, 102, 255, 153, 153, 255, 153, 204, 255, 153, 255, 255, 153, 0, 0, 204, 51, 0, 204, 102, 0, 204, 153, 0, 204, 204, 0, 204, 255, 0, 204, 0, 51, 204, 51, 51, 204, 102, 51, 204, 153, 51, 204, 204, 51, 204, 255, 51, 204, 0, 102, 204, 51, 102, 204, 102, 102, 204, 153, 102, 204, 204, 102, 204, 255, 102, 204, 0, 153, 204, 51, 153, 204, 102, 153, 204, 153, 153, 204, 204, 153, 204, 255, 153, 204, 0, 204, 204, 51, 204, 204, 102, 204, 204, 153, 204, 204, 204, 204, 204, 255, 204, 204, 0, 255, 204, 51, 255, 204, 102, 255, 204, 153, 255, 204, 204, 255, 204, 255, 255, 204, 0, 0, 255, 51, 0, 255, 102, 0, 255, 153, 0, 255, 204, 0, 255, 255, 0, 255, 0, 51, 255, 51, 51, 255, 102, 51, 255, 153, 51, 255, 204, 51, 255, 255, 51, 255, 0, 102, 255, 51, 102, 255, 102, 102, 255, 153, 102, 255, 204, 102, 255, 255, 102, 255, 0, 153, 255, 51, 153, 255, 102, 153, 255, 153, 153, 255, 204, 153, 255, 255, 153, 255, 0, 204, 255, 51, 204, 255, 102, 204, 255, 153, 204, 255, 204, 204, 255, 255, 204, 255, 0, 255, 255, 51, 255, 255, 102, 255, 255, 153, 255, 255, 204, 255, 255, 255, 255, 255]
Data: [(0, 255), (57, 255), (65, 255), (208, 255)]

Expected something closer to:

Palette: [[Black][Red][Green][Blue]]
Data: [(0, 255), (1, 255), (2, 255), (3, 255)]

[radarhere]

I've created #9153 to resolve this. With that, your script outputs

Palette: [0, 162, 232, 34, 177, 76, 237, 28, 36, 0, 0, 0]
Data: [(3, 255), (2, 255), (1, 255), (0, 255)]