Hello! could you please post your export settings to see what is causing the slow down? Regarding optimization, you can likely append the skins at runtime since you are not using meshes (at least from what I can tell from the screenshot). But I will ask Harri to chime in

You could theoretically place the single images in your Unity project as Sprites and attach them to the Spine Skeleton, as shown in the example scenes Spine Examples/Other Examples/Mix and Match and Spine Examples/Other Examples/Mix and Match Equip that come with the spine-unity unitypackage. You could then pack the atlas at runtime as in the examples, which would be only a small atlas per character.

However I would not recommend going down this path, as all your assets of the 420 folders should fit into two 2048x2048 textures. Having all characters on two atlas pages would be preferable in terms of draw calls, unless you always only have a single skin of the 432 showing in the whole scene.
Could you please post a screenshot of the Texture Pack Settings that you have used? Especially the Packing type under Output would effect the time and resources it takes to pack, did you try different settings here: Grid, Rectangles and Polygons? I would guess that e.g. Polygons could be problematic at such a high image count.

You could also try packing multiple smaller atlas pages by setting the Max width and Max height to e.g. 1024 or 512 instead of 2048.

Packing Skeleton and atlas separately
In general I would suggest not packing the texture atlas along with the skeleton, but exporting the Skeleton without the Atlas first (Texture atlas: Pack disabled), and then exporting the atlas separately as described here.

If this still fails, you could also try adding a very simple pack.json file in folders that you want separate pages for, and export the top directory with option Combine subdirectories enabled - it will then go over all your subdirectories and process them at once, with the pack.json files acting as atlas page separators.

hyodongwoo wrote

I exported with the 'Grid packing type' of the output setting and It works smoothly! However, there are too many images :think: is this the only way to export my file??

Sorry to hear that there are still problems remaining.
Are the exported textures that you show of size 2048x2048, or 1024x1024 or smaller?
Is each one of the atlas texture pages of the same size and fully packed? Or are some half-empty? If they are only partly filled, could you please check if there are any pack.json files in any of the texture subdirectories?

Have you tried executing the texture packer separately (separate from the skeleton export as described in my previous post)?

Thanks for your detailled reply!

Your screenshot shows a pack.json file in the subdirectory 128images/b1~5.
Now an important question: Is there a pack.json file in every subdirectory, like one in b6~10, one in b11~15 and so on? If that is the case, then you can delete them (or move them to a backup location in case they had a purpose) from the subdirectories, otherwise each pack.json file will result in a separate atlas page. The single pack.json file at the top directory 128images can stay as it is.

Thank you for the clarification.

You could place every ₅ (or 10?) of your subfolders into a new parent folder with a pack.json file only in the parent where you are receiving too many "narrow" atlas textures (e.g. 256 x 2048 px), and remove the pack.json file from the ₅ subfolders. This should then combine the ₅ subfolder atlas textures to a larger one.

Anyway, it is a pity that export is "not going well" otherwise, as this should all be done automatically.