Trouble because secondary GI multplier isn't working in GPU mode

[Micha]

Hi,

The theory says that in the real world the brightest white reflects a maximum of 80% of diffuse light. In rendering, this means staying below gray level 204 for white areas. But when working with color systems like Panotone, it is annoying to correct all colors with a factor of 0.8. But without correction, shaded areas become too bright.

In the past I set the secondary engine multiplier to 0.8 and everything was fine. Now I noticed that in GPU mode this option is ignored. Please adjust the code so that this option also works in GPU mode.


Best regards,
Micha


<Asset renderer="vray" url="/SettingsGI" type="settings" layout="">
<plugin>
<vrayplugin name="SettingsGI" type="settings" version="19">
<parameters>
<parameter handler="default" label="secondary_multiplier" name="secondary_multiplier" listType="none" type="float">
<value>0.8</value>
</parameter>

[vladimir_krastev]

Hi, thanks for posting. The options for adjusting the GI multipliers are deprecated. It is better to try to adapt our workflows to that. Even in the past when they were available it was not recommended to use them.

[Micha]

Hi vladimir_krastev so, it would be great to get an option to make all color inputs physical correct. Please don't oversee, all textures, all design color systems are using (255,255,255) for white but this white doesn't exist at the real world. It's cumbersome to correct all colors and textures or rendered results maybe incorrect looking. A global correction multiplier should be very useful.

[vladimir_krastev]

Could you elaborate on this idea a little? The 0-255 colour system is industry standard and the render engines use it and are built to comply with it. Can you give us an example of the benefits of this clamping or global correction multiplier?

[Micha]

If your design system is using colors between 0-255 and the user use it, than V-Ray calculate a 100% diffuse light transport for full white. This isn't physical correct and can cause a wrong, dull look. I run in the problem of the dull look and tried to decrease the diffuse light transport like I did it in the past per CPU mode but it doesn't work anymore.

[Micha]

Is now a better time to talk about this basic issue?

Here two example - the dull 100% light transport per wall color (255,255,255) and the natural looking light fallof by a wall color with (205,205,205)

[vladimir_krastev]

Hi, thanks for the examples.

it is annoying to correct all colours with a factor of 0.8. But without correction, shaded areas become too bright.

You can bring back and adjust tone and intensity however you like as a post process.

[Micha]

No, it can not work per post process. If to much light is transported to areas where not much GI should be, than you can't correct it. Also don't forget if colors and textures are at the room, than a strong correction will cause color issues.

Here the above 255-Example corrected - shadows are still dull and details are gone. Look at the right side from the bed. The shadow of the table is blurry and dull, because to much light is transported to this area. Or look at the right door frame of the open bath - the frame lost his light-shadow contrast. You can not correct a wrong GI light transport per postwork.

It's an essential feature and users will much easier get the right look, most for light colored interior scenes, if the light transport can be limited to 80% for full white. I often render train and air plane interiors since years and I'm tired to correct all colors and textures down to 80% now. In the past per CPU it was much easier to get a natural and lively look.

Please bring back the good old correction parameter, it was an important feature.


255-255-255 Version corrected in postwork


Physical correct white 205-205-205