Is your normal map upside down? Find out, fix it, prove it.

Every artist has seen it: bumps that look like dents, a bevel lit from the wrong side, a map that looks fine in one program and inside-out in another. The usual reason is the green channel. OpenGL and DirectX normal maps are identical except that green points the other way, and nothing in the file says which one you have. Substance Painter will not guess; most tools just convert "by instruction" and trust that you picked right.

NormalProof checks every normal map on your object against an independent reference, tells you whether the Normal Map node reads it the right way, and fixes it — then checks again to prove the fix.

Checked against something real, not guessed

A map cannot tell you on its own which way it points. So NormalProof compares it with something that can:

• Your high-poly. Select it with the low-poly, and Blender bakes its own reference of the same pair. The green channel is compared texel by texel. On 44 CC0 models it confirmed the right map and caught the flipped one on 41, and said it could not tell on the other 3 — it never gave a wrong answer.
• The material's height map. No high-poly? If the material has a height or displacement map on a Displacement or Bump node, its slopes are the reference. On six CC0 material sets that ship both an OpenGL and a DirectX map, every verdict it gave was right.

The red channel is the same in OpenGL and DirectX, so it serves as a control: when the reference and the map do not agree even on red, the add-on says it cannot tell instead of guessing. With neither a high-poly nor a height map, it says there is nothing to check against.

It reads what the node actually receives

NormalProof does not guess from node names. It bakes exactly what arrives at the Normal Map node's Color input — through reroutes, mixes, a flip you already built — so what it checks is what Blender renders. On Blender 5.x it also reads the node's own OpenGL / DirectX switch.

One click to fix, and the proof

• Flipped green channel: on Blender 5.x the node's Convention is switched; on 4.2 a flip is inserted in front of that node, in that same connection. Press Fix again and it is taken back out.
• Normal map read as colour (sRGB): set to Non-Color — unless the same image is used as a colour somewhere else in the file, in which case it tells you to make a separate copy instead of breaking that material.
• After every fix the check runs again, and the panel shows the result.

Your scene is left as it was

The bakes run on temporary copies with their own materials and images. Your objects, materials, images, bake settings, render engine and selection are exactly as they were afterwards — checked, not assumed.

Why the numbers are trustworthy

35 to 36 automated checks (one needs the node switch that 4.2 does not have), zero problems, on Blender 4.2.9, 5.1.0, 5.2.0, 5.2.1 and 5.2.2. Fourteen deliberate breakages of the checking and fixing code were introduced one at a time, and the checks caught every one. On 51 real CC0 production files, the add-on looked at the 192 objects' own normal maps with no reference and raised no false alarm on any of them. On 44 of those models paired as high-poly and a reduced low-poly, it confirmed the baked map on 41, found the flipped copy and proved the fix on the same 41, and on the other 3 said it could not tell — no wrong verdict on any model.

Blender 4.2 and newer. Cycles (for the reference bakes). Sidebar tab: NormalProof.

License

GPL-3.0.