How to remove baked lighting from textures (and why AI textures have it)

Albedo: colour without light

In a modern PBR material, the colour texture is called the albedo or base colour. It is meant to be the colour of the surface itself: what a red brick looks like under perfectly even light, with no shadows, no highlights and no bright side. The renderer adds the light later, from the lights in the scene.

If the albedo already contains light, the scene adds light on top of light. Shadows double up, a dark side stays dark even when the sun moves round to it, and the model never quite sits in its environment. That is why game artists care so much about a clean albedo. PBR maps explained covers the other maps in the set.

Why AI-painted textures carry lighting

AI texturing paints a model by repainting rendered pictures of it from several cameras and projecting those pictures back onto the surface (how projection texturing works). Image models learned from photos and renders, and almost every photo has light in it. So when the model paints a view, it tends to paint a plausible light as well: a darker underside, shading in folds, sometimes a soft cast shadow.

Our studio asks the image model for even, flat lighting with no cast shadows, and that helps a lot. But it is a request, not a guarantee. Some shading still gets through, and because each view is painted separately, the light can differ a little from view to view. Where two views meet, that can show as a patch that is lighter or darker than its neighbour. Auto texture already runs a colour match between views to reduce this; delighting deals with what is left.

Photo-scanned (photogrammetry) textures have the same problem for a simpler reason: the photos were taken under real light, often outdoors, so the sun and sky are in every pixel.

How texture delighting works

Every delighting method tries to split the texture into two parts, surface colour and lighting, and keep only the colour. The hard part is that a dark patch could be either: a shadow on a light surface, or a light-coloured surface that is really dark. Tools answer that question in different ways:

• Use the model’s shape. If you know the geometry, you can predict where light is blocked (ambient occlusion) and which way each part faces, and undo the brightness those would cause. Unity’s experimental De-Lighting Tool, released in 2017 for photogrammetry assets, worked this way, using AO, normal and bent normal maps of the asset.
• Ask the user. Agisoft De-Lighter, a free tool released in 2019, has you mark which areas are lit and which are in shadow with a few brush strokes, then removes cast shadows and AO from photogrammetry textures based on those hints.
• Use smooth brightness. Lighting usually changes slowly across a surface, while colour detail changes quickly. So you can estimate the slow brightness changes with a wide blur and divide them out, keeping the fine detail. This is simple and fast, and it is what our studio does.
• Train a model. Research systems learn to split images into albedo and shading from large sets of examples. These can handle harder cases, but need a GPU model to run.

The best delighting is the light you never bake. Asking for flat, even lighting in the prompt, or rendering your bakes with no lights, saves most of the clean-up.

Remove lighting in the AI 3D Texturing Studio

In the AI 3D Texturing Studio, box 4 PBR maps has a checkbox called Remove lighting (evens out baked shadows and dark sides). It is free, it runs in your browser, and it works on whatever you painted in the studio, with Auto texture, Paint this view or the free brushes.

What it does

It looks at your painted texture at low resolution, works out how bright each area is compared with the model as a whole, and brightens the dark areas and tones down the bright ones towards that average. The comparison uses a wide, soft blur, so fine detail such as stitching, wood grain or small painted marks is kept. The correction is done in linear light and keeps each colour’s hue instead of washing it out to white.

The Remove lighting slider runs from 0.1 to 1 and starts at 0.8 when you tick the box. Lower values keep more of the original shading; 1 applies the full correction.

How to use it

1. Paint the model first (for example the bear sample with Auto texture). The PBR box stays disabled until something is painted.
2. Tick Remove lighting and press Make PBR maps. The preview switches to the full PBR material.
3. Turn the model round. If dark sides are still visible, raise the slider; if the colours look flat, lower it.
4. Download. While the PBR preview is on, Download textured model (GLB) carries the evened-out colour plus the normal, roughness, metal and AO maps. PBR maps (PNG) gives you albedo_delit, normal and ORM images (AO in red, roughness in green, metal in blue).

What it cannot do

This is a fast browser approximation, not a trained delighting model, and it helps to know its limits:

• It cannot tell dark paint from shadow. A large area that really is dark, such as black boots on a light outfit, gets brightened too. Lower the slider for models with big dark parts.
• Sharp, small shadows and highlights stay. It evens out broad shading and dark sides. A crisp cast shadow under a strap, or a small shiny spot, is too fine for the wide blur to catch.
• It works on the texture, not on the 3D scene. It does not know where the light came from; it only evens out brightness across the painted texture.
• It only works on paint made in the studio. The studio starts every model from grey clay, so it does not delight a texture that was already in your file.

For the patches it cannot fix, repaint them: brush over the area with Select region and press Paint the marked part, or use the free Heal brush on small spots. Fix grey spots on an AI-textured model and Repaint one part of a 3D model show how.

Questions