Chroma subsampling in AVIF conversion

[YouriAndropov]

Hi,
I'm converting PNG files to AVIF using Magick.NET in PowerShell, but I can't get 4:4:4 chroma subsampling to work. None of these attempts have had any effect:

$OldImage.SetAttribute("sampling-factor", "4:4:4")
$OldImage.Settings.SetDefine("avif:chroma-subsample", "0")
$OldImage.Settings.SetDefine("sampling-factor", "4:4:4")
$OldImage.Settings.SetDefine([ImageMagick.MagickFormat]::Avif, "chroma-subsample", "4:4:4")

The output always shows YUV 4:2:0 when inspected with ExifTool.
Is 4:4:4 supported for AVIF in Magick.NET? If so, what's the correct way to set it?
Thanks.

[dlemstra]

It looks like I will need to add a new HeicWriteDefines to simplify this for you. For now you should set heic:chroma to 444. You need to use heic here instead because that is the module that contains the avif encoder.

[YouriAndropov]

It worked as intended, thanks a lot.

[YouriAndropov]

Hi Dirk,

Just a friendly follow-up on this one: I've updated to 14.17.2 and heic:chroma is still working fine for me, so no rush at all. I noticed HeicWriteDefines hasn't landed yet (only HeicReadDefines is there), so I wanted to check whether it's still on your list.

Having a typed Chroma property would make AVIF 4:4:4 encoding much easier to discover — I spent quite some time trying sampling-factor and avif:* defines before asking here.

Thanks again for your help and for Magick.NET!

[dlemstra]

I just pushed a change that adds the HeicWriteDefines. This will become available in the next release (15.1.0).