How to save "nclx_profile" in a HEIC image?

[wiggin15]

I'm trying to add the "nclx_profile" metadata to a new HEIC file.
I'm setting this key as a dict in pil_image.info, but when I save and load the photo the data isn't there.

Full example code to reproduce:

import numpy as np
import pillow_heif
from PIL import Image
from io import BytesIO

from pillow_heif import register_heif_opener
register_heif_opener()

nclx_profile = {
 'color_primaries': 1,
 'transfer_characteristics': 2,
 'matrix_coefficients': 1,
 'full_range_flag': 1,
 'color_primary_red_x': 0.0,
 'color_primary_red_y': 0.0,
 'color_primary_green_x': 0.0,
 'color_primary_green_y': 0.0,
 'color_primary_blue_x': 0.0,
 'color_primary_blue_y': 0.0,
 'color_primary_white_x': 0.0,
 'color_primary_white_y': 0.0
}

# create a new, blank image
pil_image = Image.fromarray(np.ones((16, 16, 3)).astype(np.uint8))
# sset nclx_profile
pil_image.info['nclx_profile'] = nclx_profile
# save to an in-memory file (works if we save to disk too)
tmp = BytesIO()
pil_image.save(tmp, format="heif")
# re-open the image and see if nclx_profile is there
Image.open(tmp).info['nclx_profile']    # KeyError!

[bigcat88]

I am not sure that it is not set, need to check, earlier versions of libheif was able to set it, but was not able to retrieve it after set, as libheif does not support reading of nclx embedded in stream and not in image.
And during encoding libheif embeds it in stream.
I will take a look today at this.

[bigcat88]

https://github.com/strukturag/libheif/blob/794a791b5048ff2bcdb6507c4413719652f568cf/libheif/heif.h#L997-L1002

When libheif will add such ability, I immediately will add tests for this in pillow_heif, as I myself waiting for it.

[wiggin15]

Are you saying that the NCLX data is indeed stored, but not read?

I have a HEIC file (that I can't share, unfortunately) where there are multiple images and each of them does have the information read correctly by pillow-heif

from pillow_heif import open_heif
i = open_heif("myfile.heic")
i[0].info['nclx_profile']  # working
i[1].info['nclx_profile']  # working

I'm trying to construct a similar file using:

primary_pil.save(..., append_images=[secondary_pil])

and putting the nclx_profile on both PILs' info.
I'm not entirely sure how my HEIC was generated but I'd be surprised if they didn't use libheif themselves...

[bigcat88]

This is real, a perfect issue.

Thank you for pointing on this.
Need to set macOS_compatibility_workaround_no_nclx_profile flag to false, to make it works.
But in current version it is not possible.

Will try to do a fix for a new one that is coming.

[bigcat88]

Done. New version will be published, as soon as Python3.12 RC1 will come and cibuildwheel will get update for it(early August).

[bigcat88]

done, new version is out

[bigcat88]

P.S.: In new upcoming version #171 NCLX is saved by default.