PBR Material and Linear Color Space in Movie, TV and Engine

Renderwow - 3/7/19 18:38

linear space

Linear material should be familiar with it. it's the physical materials that are widely used in games, movies and TV nowadays. There are many ways to implement pbr, and different PBRs have different characteristics. Nowadays PBR is always associated with linear space, although they are not absolutely dependent, but it's all about making rendering more real and rational.

PBR needs to define more clearly that mappings are linear on non-intrinsic color maps. The reason is that inherent color mapping generally requires human perception, and because of the legacy of history, most intrinsic color maps require human eye perception. Gamma correction problems arise from human eye perception, technology goes into detail, because many technology blogs mention it, the popular saying is that the color of an object seen by the human eye has actually been processed by vision and the brain, it's not the color of the object.

Under the same light setting, Untiy3d is easily exposed by default using the left gamma mode, on the right is the linear setting, not easy to expose.

Object effects in linear space, the greatest advantage is the nature of light, especially in the attenuation of light and shadow on the surface of an object.

Here's a comparison chart.

Maya 2016 Arnold 4 adjusts as much as possible to the same ambient brightness, the right side is linear

Objects in off-line rendering are also prone to over-exposure in non-linear space, or grey, previous production usually used to adjust this problem by adding lights and other means.

So the inherent color is usually labeled sRGB, it means that this is the color seen in the human eye, in this way, the computer can convert such pictures into linear ones internally, to make the whole scene mapping calculation more natural, Instead of sRGB mapping, visualization is usually made out（Such as substance painter nowadays）.

Real Time Rendering

Unity3d defaults to gamma space, this is because linear space needs to support OpenGL ES 3.0, some mobile phones and Macs do not support it.

Unity3d Overall Linear Space and Picture sRGB Settings

The default in Unreal 4 is linear space, that's why many UE4 projects have a good texture, the format of texture processing still needs to be adjusted by the producer according to the actual situation.

offline rendering

Maya 2016 and previous settings are still a little cumbersome

In the past, the settings of old versions were rather tedious, that's why many rendering projects used to be less effective than those in engines（Of course, there are many other questions. I'll talk about them later）, not only do you need to change your color space, do you need to connect nodes to set the image to be linear（Because previous versions of Arnold did not recognize the texture information in Maya）. But after 2017, Arnold 5 has been integrated into linear space as Maya defaults, all you need is whether the picture is raw or srgb.

It can be seen that both linear space and PBR are necessary.

Production link PBR

Here I want to say that the next color maps are sRGB.

Normal mapping is linear, but in the past, software can automatically recognize normal maps. Many producers can draw normal maps by hand. why is that? because of proficiency...

The HDR environment maps used before are actually linear, someone asked, is the mask map or 3S map linear? the answer depends on your production environment, if it is now made in pbr-related DCC software, so these maps are linear, if it's previous material, That eight Chengdu is Srgb, because software used to be mostly non-linear, the mapping effect depends on the right side, so nowadays sRGB can be calculated in linear space, although most of the maps still need to be re-patched.

General producer unless the project specifies a metal（Or high-precision projects）, in fact, it does not need to be concerned about which color represents the degree of metallicity, what is the roughness, because we only need to observe and adjust texture export maps in relevant software, put it in other software, or rendering or real-time, the overall effect is right. Now related mapping software such as SP and SD can directly preview the effect of PBR material in the correct linear space.