I modeled this apple, and as far as I know there doesn't seem to be anything wrong with the mesh... except I keep getting this split down the middle along the seam. There's nothing in the texture which would explain it. Can someone help me out by explaining this?

My guess is you need to check the normals on each half.

Does seem like a normal issue did you use a mirror modifier and perhaps did not apply it and make sure that clipping was checked and after applying it making sure you remove doubles?

Lobo3433 posted at 11:45AM Sun, 10 May 2020 - #4388705

Does seem like a normal issue did you use a mirror modifier and perhaps did not apply it and make sure that clipping was checked and after applying it making sure you remove doubles?

I checked and I did have a modifier attached, but not applied, and I did remove 34 doubles. That didn't fix it, but I think I'll scrap it and start again. I have several apple types anyway, so a little diversity will help.

Before you ask, yes, I did try to fix it, but I made it worse. Don't know what I did exactly, but that hole shouldn't be there. It's not in the mesh.

Looks like something got merged that shouldn't have there use to be a tool that has not been updated for 2.8 that I wish they would or at least get it working properly for 2.8 called Meshlint it was great in 2.79 and would show you all the info about a mesh like if it you had ngons and if verts were over lapping very useful but the current 2.8 version is still buggy

Actually, I still use 2.79. My computer's too old for 2.8. I'll check for Meshlint.

In your original post, that issue looks exactly like a mirroring issue. The UV's weren't mirrored or the mesh itself was not mirrored properly and didn't accept the mirrored UV's on one side. It doesn't look like a normals issue, but I haven't worked with 2.79 in years, so I don't really remember if that's something I've seen before with the normals.

The black spot looks like artifacts I've seen happen with baked textures where vertices somehow get out of alignment with the UVs during lighting calculations. I'm going to assume you didn't do any baking on this project, so that's probably not what happened there.

I definitely would start this model over again, because there's a number of issues there which may or may not be "fixable" at this point. Luckily it's a very simple mesh so it shouldn't take much time to start from scratch. If it's not too much trouble and you wouldn't mind sharing the .blend file of that problem mesh, I'd love to have a look at it. Especially the black spot is something I've only seen before with baking issues, so I'd really be interested to know exactly what could be causing that. If you can't share the file I understand. Good luck on the new model.

I'm beginning to think the problem is not the mesh, but somehow, the texture. I created a UV sphere yesterday, and used the same texture on it. I didn't do anything to the sphere, but got pretty much the same problem. I'm going to dump the texture and try another one to see what happens.

You're not baking/using a normal are you? Cause I can pretty easily create a very similar seam issue by baking a normal to geometry that isn't welded/merged at the seam, then welding/merging the seam and applying the normal map, or vice versa.

Does the seam persist if you apply the same half of the texture, to both halves of the model?

In this instance yes, because I've done this before. Either I never noticed it before, or it's more pronounced.

Same thing, different texture.

what you're seeing is the seam caused by the way you uv mapped it. The texture is mottled lighter red and darker red and they aren't lining up.

Looking at your apple texture, @RedPhantom is right, that's just not going to line up the way it is right now.

You can see on the one half you've got two light spots, with a dark spot in the middle near the pole, on the other half, you've got almost the opposite of that, two darker areas with a lighter spot at the pole. That's going to make for a very obvious seam.

You can fix it pretty easily in Blender with the texture painting tools, focus on the seam areas, you shouldn't have any problem painting that out. Just a matter of some color picker and painting, shouldn't take more than a few minutes to clean up.

You could also, flip the UV layout for one half, over lap the two halves in the UV layout, making sure that corresponding points along the seam line up. This will give you a mirrored texture for the two halves, not ideal, but an option, and it will sort out the seams.

Alternatively, and this is a LOT more laborious process, you can create a second UV map for your object [doesn't have to actually be the whole object, just the seams, and enough space either side to work with], changing where you put the seams, so that the seams on the second UV map are different from the first. Then bake off your textures from the current UV layout/texture set, to the new UV layout. Since the seams are different, you'll have the problem areas from your current texture at a place where you're able to work on them on the new texture. Paint them out, then reverse the process, baking the cleaned up seams back to your original UV layout. Not sure I'd go this route given the relative simplicity of the objects and textures in this case, I think the texture paint in Blender would be good enough, and far far quicker.

Okay, looks like you were right. I basically just made a quickie texture of one solid color, red, and re-textured the apple. Viola'! seam gone! I'll have to do a much better job at texturing.