Alpha channel with unci tiled output?

[jerstlouis]

I initially dismissed this as a potential bug in GDAL, but it seems that our unci tiled output is missing an alpha channel.

For example this output should be padded with transparent pixels:

https://maps.gnosis.earth/ogcapi/collections/blueMarble/map.heif?width=1000&tile-size=256

heif-info will say:

image: 1024x512 (id=1), primary
  tiles: 4x2, tile size: 256x256
  colorspace: RGB
  bit depth: 8
  color profile: no
  alpha channel: no 
  depth channel: no

The alpha channel is working fine when not using tiled output.

We're using heif_colorspace_RGB, heif_chroma_interleaved_RGBA to create the prototype image and the encoding_options passed to heif_context_add_unci_image() has save_alpha_channel set to true. Could this be a current bug or limitation in libheif?

Thanks @farindk !