How to preserve my input textures during a remesh?

About this document

In the remeshing process, the input model gets reconstructed from scratch, UVs are generated and textures are baked. As the newly generated mesh has different UVs, the original texture will not be displayed on the mesh correctly. 

Texture Baking

Texture Baking is the process of transferring 3D surface details into a 2D texture. Baking also allows for textures of one model to be transferred onto a different model. This can include surface normal information, ambient occlusion, position maps, and much more. 

Texture baking is automatically included in the remeshing process and by default transfers original texture information onto the newly generated model.
In cases where the input model has a normal map for surface details, additional steps are taken where a separate normal map is generated for the geometry and is then combined with the original detail-normal-map and recalculated, to match the newly generated mesh. 

To bake textures when remeshing, navigate to the 'Texture Output' Tab and select the desired textures you wish to have baked out. The 'Object Space Normal' and 'Custom Material Texture' maps are selected by default. 

The Custom Material Texture bakes out the 'Diffuse' Texture. The channel is labeled as the 'Custom Material Texture' because it can also bake out any other custom textures as well.

If the same texture is applied to multiple input meshes, the UV's cannot be stacked and will be packed next to one another due to the nature of remeshing. This UV stacking is not possible because new UV's are generated from the newly reconstructed mesh and are therefore not identical anymore - even if the mesh might look the same, it is not and therefore the UV's are also not connected to the original ones.

If a UV stack is desired, we recommend as an alternative to remeshing, to optimize the mesh and apply a Material Merge with the feature 'Stack duplicate Shells' enabled. This UV stacking and material merging allows for optimized texture density, optimal UV space usage, and draw call reduction.

For more information on Material Merging please read the following article about ‘Reducing draw calls by Material Merging’.

'Transfer' Texture

Instead of baking new textures for each channel, users can instead use the original input textures of the original model, on the remeshed mesh. This is possible by using a 'Transfer' texture.
A 'Transfer' Texture map is used to remap the texture using the UV coordinates as is explained in this article. 

This workflow allows the remeshed model to use the same textures as e.g., the previous LODs.