AVIF output is always saved in RGB even input is L

[MimoKar]

Describe the bug

When creating AVIF in L mode, it is always saved in RGB. the mode parameter in save function is not working - when added to force mode the image is not saved.

Steps/Code to Reproduce

Try to save some image which is in L mode.

Expected Results

Image is saved in L mode

Actual Results

no image saved

Versions

3.13.1 (tags/v3.13.1:0671451, Dec  3 2024, 19:06:28) [MSC v.1942 64 bit (AMD64)]
Windows-11-10.0.27768-SP0
0.21.0
{'libheif': '1.19.5', 'HEIF': 'x265 HEVC encoder (3.5+1-f0c1022b6)', 'AVIF': 'AOMedia Project AV1 Encoder v3.11.0', 'encoders': {'x265': 'x265 HEVC encoder (3.5+1-f0c1022b6)', 'aom': 'AOMedia Project AV1 Encoder v3.11.0', 'mask': 'mask'}, 'decoders': {'libde265': 'libde265 HEVC decoder, version 1.0.15', 'aom': 'AOMedia Project AV1 Decoder v3.11.0'}}

[bigcat88]

from PIL import Image
import pillow_heif

pillow_heif.register_avif_opener()

a = Image.open("../tests/images/non_heif/L_8__128x128.png")
a.save("test.avif")

b = Image.open("test.avif")
print(b.mode)
b.save("test2.avif")

c = Image.open("test2.avif")
print(c.mode)

Output:

L
L

Can you post the minimal reproducible code so I can see what the problem is?

[MimoKar]

Hi,

yes it is showing in my case same result. So then the result colorspace is expanded from 8-bit to 24-bit in avif files?
is there a way to force it to be 8-bit in avif (pure grayscale)?

[bigcat88]

Can you share your code and the input file you are testing it on because in my tests everything is working fine.

L mode is a grayscale image

[MimoKar]

i am not sure now how to correctly check the bits per pixel value in windows. i feel that irfanview is getting innacurate.
even the hief-enc is producing 24bpp images as per irfanview