loi I think it is probably a problem with the mipmap textures, as the resolution varies depending on the zoom level of the camera. If you are not familiar with mipmaps themselves, take a look at the mipmaps introduction page in the Unity manual:
https://docs.unity3d.com/2021.3/Documentation/Manual/texture-mipmaps-introduction.html

We have discussed in the past in the following thread how to assign a higher resolution mipmap image, so if you want to do that, it would be helpful:
https://esotericsoftware.com/forum/d/18075-using-your-own-mipmaps-with-spine

loi I am happy to help you! If you need any help in the future, please don't hesitate to ask us in this forum.

loi Unfortunately it is difficult to determine the cause from the screenshot alone, so could you send us via email a minimal Unity project that can reproduce the problem?: contact@esotericsoftware.com
Please include the URL of this forum thread in the email so we know the context. Then we can take a look at what's wrong.

loi now when I zoom out, lines that weren't originally present start to appear. I followed the tutorial using GIMP,

Which tutorial do you mean? Do you mean you've created mipmaps in Gimp? Are you sure you want to set mipmap levels manually? Unless you have a good reason for it, it's much easier to either disable mipmaps if you want none, or enable mipmaps and set a mip-map bias as mentioned here.

If you have to use manual mipmaps, please describe in detail:

• How you have exported your atlas textures (export settings, whether you're using PMA or straight alpha workflow),
• What you texture import settings in Unity are. Also try to disable any compression settings if enabled.
• How you're assigning mipmap levels in code.

loi The tutorial I was referring to is the "spine-unity import trouble" guide

I assume you mean the "[spine-unity] Import Troubleshooting" video here:

In general it's best to share a link, then there is no ambiguity left.

loi I disabled premultiplied alpha, set the minimum and maximum atlas size to 2048x1024, and used a padding value of 4. All other settings were left as default.

A padding of 4 might be causing your neighbour attachments in the atlas to blur over if you display a high mipmap level. Note that when displaying the first mip level, 2 texels are blurred together, on the next level 4, then 8.

Please have a try whether increasing the padding to 8 during atlas packing changes the situation, it should then show the stripes on the next zoom-out mip-map level. If that helps, you know that you could either set a maximum mipmap level (which can also be set in Quality settings) which not to exceed, or increase the padding. Theoretically you could also ensure your attachments are of size multiples of 8 and set padding to 0 or use atlas texture packing mode grid (which is rather wasteful though). Mesh Attachments might however still potentially mess with your packing though, so it might be best to limit the mip level.

loi When unwanted lines appeared, I followed the suggestion to use GIMP to preserve color values in transparent pixels.

Glad to hear you're not setting mipmaps yourself. You used GIMP to do what then? I didn't quite get what image editing you needed to do on your exported atlas textures.

loi By the way, this is unrelated to the white seam issue caused by mipmaps, but I think you should combine the texture atlas pages for this skeleton into a single page. In the Unity package you sent us, your skeleton has three materials, but the Materials array in the MeshRenderer contains 33 entries due to an unorganized draw order. This is quite inefficient. If you haven’t already read the Rendering section of the documentation, I highly recommend doing so: https://esotericsoftware.com/spine-unity-rendering

@loi

A few general things:

1.) White pixels in your atlas texture: If you just export your atlas texture as straight alpha with bleed enabled (and this is recommended), you should always see the outermost perimeter color (black in case of your black outlines) in transparent regions when hiding alpha in a trustworthy image editor (e.g. GIMP), not white pixels (unless your outermost part was white). If you see unexpected white pixels then likely the image has been processed with an image editor which does not respect and changes RGB values in completely transparent pixels (like Photoshop does unfortunatley).

2.) Straight alpha vs. PMA: Note that if you are using Gamma color space, you could also use PMA instead of straight alpha workflow. This should improve the situation with mipmaps slightly as well. Don't expect it to solve all problems though.

Regarding your specific white lines problem

Misaki found out the following:
1) Stripe at the leg: This is indeed due to mipmaps blurring-over the white (or cream) part of the hair-attachment next to it:

So during atlas packing you need to add more padding here. Alternatively you could also disable Strip whitespace X|Y which removes transparent areas during packing and instead manually add transparent areas yourself where you need them. The latter is more tedious though obviously than just increasing the padding to e.g. 8. Misaki confirmed the white line at the leg is no longer visible when increasing packing to 8.

Another alternative workaround could be to change the region attachment into a mesh attachment and cut the mesh more tightly at just the problematic parts.

2) Regarding the white line at the skirt:

This seems to be due to the skirt part overlapping a white cloth underneath, but covering it pretty precisely with not much "safety overlap". Now when mipmaps blur your covering top-layer skirt attachment texels together, an opaque covering black skirt texel and a transparent one are blurred together to a semi-transparent black one, showing the white parts underneath. This unfortunately is a theoretical problem with mip-maps again. This could be resolved by having wider black "safety-overlap" of the skirt attachments. Alternatively you could turn the skirt into a mesh attachment instead of multiple separate region attachments - when there are no attachment borders in the middle of the skirt, nothing can show through between them. It could also be resolved to make sure that there are no white parts underneath the black ones where there should be no white showing ever, so making the white cloth parts black in these areas or adding a black cover attachment in the middle if that's not possible.

loi I'm glad that your issue has been resolved! Thank you for getting back to us!

@loi Very glad it helped, thanks for your kind words!