Hello to the support,

I run the website minecraft-heads.com and so, I am working with skinfiles and render images a lot. I came across some skinfiles, which didnt include any transparency but were still shown correctly ingame. The interesting thing: Only the inner layer was shown. Even some not transparent content on the outer layer was hidden.

So I did some research and found out, that the outer layer of a skinfile is hidden on a head if there's no transparent pixel in the whole skinfile. I attached some examples.

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UPDATE:

After a discussion with the support, the bug report is reduced to the Skinfile Preview within the Minecraft Launcher hiding the second layer of the head, if there's no transparency in the skinfile at all.

Therefor, example 3 and 4 show the behaviour.

Most likely this behaviour is somehow related to this old feature for 32x64 skinfiles, where the second layer of a head should be hidden if there's no transparency: https://bugs.mojang.com/browse/MC-101150

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Lets look at some examples:

1) No transparency, white background => shown as Jukebox on the inner layer only in the Minecraft Launcher and the game

/give @p minecraft:player_head{display:{Name:'{"text":"Jukebox"}'},SkullOwner:{Id:[I;366921839,-1320598256,-1075067766,1418073745],Properties:{textures:[{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvZWFmY2Y0NDNiNWI1MWI3MzUyNjg4OTY0ZGE0NmZkYjMzMGQwNTdjNDAzZGM4ZDJjNjdlM2M3MTY5YWRjNjM0NyJ9fX0="}]}}} 1

2) Transparency => shown as white block on the outer layer in the Launcher and the game

/give @p minecraft:player_head{display:{Name:'{"text":"Jukebox"}'},SkullOwner:{Id:[I;366921839,-1320598256,-1075067766,1418073745],Properties:{textures:[{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvMWQ2OThkMmJmMWM0OTU2OWJhYzU5NGMwZjhjMzkxN2I5OTVjZGQxMDdkZDljM2MyMDcwNmU5NTZiZWFmZmU3YiJ9fX0="}]}}} 1

3) No transparency, large skinfile => same as 2)

/give @p minecraft:player_head{display:{Name:'{"text":"Big and White"}'},SkullOwner:{Id:[I;1931365067,850149589,-1957330689,-351153852],Properties:{textures:[{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvNjE5ZjU2ZWUzMzdiOTA0MmZiNTdiMzc3MDgzMDMzZTEzNzkwMzYwNThmZDAzODZmYTdmOTc1Nzg3MGE3ZTBjYyJ9fX0="}]}}} 1

4) No transparency, large, red background => Shown as valid jukebox on the inner layer in the previewer, shown as red cube on the outer layer in Minecraft

/give @p minecraft:player_head{display:{Name:'{"text":"Big and Red"}'},SkullOwner:{Id:[I;-1387188967,-1133819370,-1119303347,820417908],Properties:{textures:[{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvMzVhOTQxMGE3MzE0MTZjNjc4ZWZmZDczYjBhNzQ5NTdlMTBkZGE5ZWVkMDFkODIxOGY1OGQ1YTI5YTU3ODU5NCJ9fX0="}]}}} 1 

5) Link: No transparency but content on the head => Link is shown without the outer layer hair, just the inner layer. White background is hidden

/give @p minecraft:player_head{display:{Name:'{"text":"Link"}'},SkullOwner:{Id:[I;-54146875,1435914048,-1833397616,-327866182],Properties:{textures:[{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvODQzZmVkZTg3MDAwNTg4ZmJkMzIzODQ0ODgwZmY1YWExZDA2ZThmMmUyMWU5ZTM1MzhlMmRjZTFjMjJlYWQ3MyJ9fX0="}]}}} 1 

Conclusions:

• If there's no transparent area in a skinfile and the background is white, the outer layer of the head seems to be hidden
  => Bug: I would expect a not-transparent area to be shown. Especially if there's content like in example 5, I would wonder why this is hidden at all.

• If there's no transparent area and the background is for ex red (example 4), the outer layer is hidden in the Minecraft Launcher but not in the game - therefor the preview does not show  the correct head.
  => BUG: Differences between the Minecraft Launcher preview and the ingame rendering of the skinfile
• I found some examples where I could also get this behaviour of hiding the outer layer on big skinfiles, but I didnt fully find it out. There's definitly a logic to hide the outer layer on big skinfiles, too.

I really wonder why there's this mechanic to hide some parts of the skin if there's no transparency at all.

If you do not plan to fix it, could you explain the mechanic? That would make it a lot more understandable and I could write a docu in the Minecraft wiki about this so people do not wonder...