Unable to change translucency using post-process material.

Ibtesam_Sadiq · November 14, 2022, 10:26am

Hi,
I am trying to change the color of translucent objects using post-process material. And it seems like it is not working. I am unable to manipulate the translucency in post-process material.

Note: I am using the “Before Tone Mapper”.
I also tried “Before Translucency”.

It seems like the unreal engine doesn’t support translucency manipulation through post-process material.

EliasWick · November 14, 2022, 2:07pm

Which Scene Texture are you using? Have a look at this documentation: Post Process Materials | Unreal Engine Documentation

Blendable Location Description

Before Tonemapping PostProcessInput0 provides the scene color with all lighting in HDR. Use this to fix issues with temporal antialiasing and GBuffer lookups e.g. depth, normals.

After Tonemapping Preferred location for performance as the color is LDR and therefore requires less precision and bandwidth. This is after tone mapping and color grading.

Before Translucency This is even earlier in the pipeline than ‘Before Tonemapping’ before translucency was combined with the scene color. Note that SeparateTranslucency is composited later than normal translucency.

Replacing the Tonemapper PostProcessInput0 provides the HDR scene color, PostProcessInput1 has the SeparateTranslucency (Alpha is mask), PostprocessInput2 has the low resolution bloom input.

Note:

PostProcessInput1 has the SeparateTranslucency (Alpha is mask).

Ibtesam_Sadiq · November 14, 2022, 3:43pm

am I doing something wrong even if I use the 4th channel as a mask it gives highlights everything as white while keeping translucent in its original color? but if I invert that mask it changes everything to black and still keeps translucent in its original color.
which doesn’t seem right.

Ibtesam_Sadiq · November 14, 2022, 4:39pm

I don’t want to replace the tone mapper.
And It only works correctly if I change the post-process blending mode to “After Tone mapping” which provides the LDR color, without AA and depth. so I can’t use this as well.

Ibtesam_Sadiq · November 14, 2022, 4:45pm

For example, if I want to change the color of the translucent water plane using post-process material then I can’t with this mask.

very-nervess · July 24, 2023, 11:06pm

Hi, Did you ever figure this out?

Ibtesam_Sadiq · July 28, 2023, 7:22pm

unreal engine itselt doesn’t allow it. let me know if you find anything.

Blendable Location	Description
Before Tonemapping	PostProcessInput0 provides the scene color with all lighting in HDR. Use this to fix issues with temporal antialiasing and GBuffer lookups e.g. depth, normals.
After Tonemapping	Preferred location for performance as the color is LDR and therefore requires less precision and bandwidth. This is after tone mapping and color grading.
Before Translucency	This is even earlier in the pipeline than ‘Before Tonemapping’ before translucency was combined with the scene color. Note that SeparateTranslucency is composited later than normal translucency.
Replacing the Tonemapper	PostProcessInput0 provides the HDR scene color, PostProcessInput1 has the SeparateTranslucency (Alpha is mask), PostprocessInput2 has the low resolution bloom input.