Can you email the project and images? contact@esotericsoftware.com It could be due to how the images were created, but I'd like to take a look at it. Maybe I can fix it in the editor and texture packer, so there would be nothing special you need to do when creating the images.

Thanks, I just took a look at the project. Seems to be caused by Linear filtering. Turning it off removed the black borders but of course you end up with a far more pixelated look then. Nate will also be looking into it.

Fixed in 1.4.26, thanks!

The problem occurs because linear filtering samples the RGB values of neighboring pixels. It doesn't care if those neighboring pixels have an alpha of zero. This means the RGB of pixels you cannot see affects the pixels you can see!

There are two ways to fix this for your runtime code: 1) Use premultiplied alpha, OR 2) I added a texture packer setting called "bleed". This copies the color of neighboring pixels to the pixels that have an alpha of 0, which fixes the issue for non-premultiplied alpha.

It's weird that this happens inside Spine Editor though.

It doesn't anymore, Spine now converts all images to premultiplied alpha in-memory when they are loaded. The problem in the editor was the same as it would be in a runtime (wasn't using premultiplied and the source images had strange RGB values in pixels with zero alpha). The editor actually uses spine-libgdx.

Yeah, weird thing is that I've never exported premultiplied alpha-formatted for images I use to animate in Spine Editor ('cause Photoshop can't really do that anyway) and this sort of thing never happened to me. It's always been really clean. I assumed either Spine had always done the conversion behind the scenes when loading images or it wasn't using a premultiplied alpha blending shader.

The only premultiplied alpha export I've ever done was for making the texture atlas and sheet.

And from what I've seen just opening PNG files in various places though, Photoshop already makes the bordering RGB values bleed into the transparent pixels anyway.

So that made me think it was some weird program or unusual export settings that caused it that Spine wasn't automatically handling (if it made sense for it to handle at all).

Anyway. Weeeerd.