How to create a grid HEIF

[TimYao18]

I saw the code do ImageGrid::write() but I don't know how to use it. I think this is related with Box_iref, iloc and iinf box.
Is there spec or handbook to do this? I have 23008-12 and 14496-12 spec but don't understand how this works..
Could somebody give me some hint?

And is iref_box can reference to single image encoding, not grid?

[farindk]

(Duplicate of #648)

Writing tiled images are not supported yet, but I think this is something we should now finally add.

The easiest way to understand how these images work is probably to look at an example. Basically all HEIC images from the iOS camera are tiled and you can have a look with heif-info -d how they are structured. However, it won't be easy to add in a PR.

Tiled images have a "master" image of type grid:

| | Box: infe -----
| | size: 21   (header size: 12)
| | item_ID: 49
| | item_protection_index: 0
| | item_type: grid
| | item_name: 
| | content_type: 
| | content_encoding: 
| | item uri type: 
| | hidden item: false

which references all tiles:

reference with type 'dimg' from ID: 49 to IDs: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Each of these images is encoded like a normal image.