libheif fails to read supposed 12-bit uncompressed HEIF that heif-enc just wrote

[bobfriesenhahn]

I believe that this is due to a subtle bug in heif-enc related to the HDR/SDR issue.

heif-enc --verbose --bit-depth 12 --uncompressed -o heif-uncompressed-12.heif input_truecolor.png

produces a file that libheif fails to read (returns a null pointer for a plane).

But this works:

heif-enc --verbose --bit-depth 12 --uncompressed -o heif-uncompressed-12.heif input_16.png

The two PNG files are attached.

input_16.png.gz

input_truecolor.png.gz

The resulting output should look like this:

[bobfriesenhahn]

The "12 bit" uncompressed file that heif-enc writes, and GraphicsMagick can "successfully" read appears to be corrupt in that the samples are at wrong levels so the gradient is lost. A PNG file which shows what I see is attached.

The exact same code path is used to read 12-bit AVIF, and that looks fine.

[bobfriesenhahn]

GraphicsMagick has no HEIF writer at all yet, but I think that the reader is pretty much done (in the development code) and it is able to handle arbitrary bit depths (e.g. 9 if that was to somehow appear). It is useful to have on the side to see what happens.

[farindk]

I checked your files. I get it the other way around:

• input_truecolor.png is a 8 bit RGB PNG. The (--bit-depth option has no effect, since it is 8 bit input). It encodes and decodes fine with the uncompressed codec.
• input_16.png is a 16 bit greyscale PNG. It encodes or decodes incorrectly with the uncompressed codec.

I'll now check where the incorrect coding comes from...

[farindk]

Encoding 16 bit for monochrome and YCbCr is currently unsupported in the 'uncompressed' codec. This will be implemented in v1.22.0. I have added at least an error message when one tries to do so.

$ heif-enc input_16.png --bit-depth 12 --uncompressed -o heif-uncompressed-12.heif
Could not encode HEIF/AVIF file: Unsupported feature: Unsupported data version: Unsupported colourspace