@Occultcg posted a new topic, subject "Color reflection (bleed)". It read:

   Hello there!
    
    I have a problem with color reflection:
    
    cb1.jpg1147×392 67.5 KB
    
    The materials of the wall and the shelf are default (simple diffuse) (Cycles Render).
    
    The light is a Sun (Strength - 7).
    
    Render - Light Paths - Diffuse set to zero, doesn't work well as it kills the warmth of the color…
    
    Also tried to play with various combinations of settings in the “Light Paths” section of the Render settings to no avail.
    
    Is there a good method to fix this ?
    
    Thanks!
    
    P.S. I'm not even sure if this is the right place for this post… Should it be in the “Lighting and Rendering” section ?

Then @Acrivec said

    Are you sure you want to get rid of this? That's physically accurate.

After which, @Occultcg added

    This is what i was looking for !
    
    Though it is strange completely without it (in 2.79 at least)…
    
    In 2.79 works without the second Diffuse node (the white one).
    
    Is there any way to still have it but make it less visible ?
    
    Thanks!
    
    P.S. It seems that this effect, in 2.79, is stronger.
    
    Edit: It seems that it`s actually working with the second node. But it needs to have the same color and in order to make the reflection less visible, the color must be desaturated (more desaturation = less color reflection).

@CarlG (CarlG) replied

    Acrivec:
    
    > That's physically accurate.
    
    Actually it's not, for several reasons:
    
      1. No materials are perfect diffuse. Some of the current diffuse bounce should be turned into glossy bounce which doesn't normally color the outgoing ray.
      2. Our albedos tend to be a bit on the high side and saturated side.
      3. Muddling of the colors doesn't occur accurately because we stop after n bounces and energy.
      4. MIS will actively search out the strongest contributing paths.
      5. Light doesn't **really** absorb and reflect the way we approximate it, not a spectral renderer etc.
    
    
    
    Most (all?) renderers can suffer from this. I have a node group that exposes the previous shader input and the color that goes into it. Within the group I just desaturate slightly what goes into the replacement, as well as brightness and local disabling control. Rarely does it bother me so much I actually use it though - certainly not something I'd put on all materials just because.  
    
    
    BleedControl.jpg2560×1532 335 KB
    
    As for other renderers, search on youtube:  
    https://www.youtube.com/results?search_query=controlling+color+bleed

@Acrivec replied

    Effect, not shader.

So @Occultcg replied

    @CarlG I'm not sure how to apply this to a simple ‘‘Diffuse node'' (i tried to replace the “Group Input” node with a ‘‘Diffuse node'' but it doesn`t work).
    
    Can you please guide me ?
    
    Here is the file if you need it: cb.blend (530.9 KB)
    
    Thanks!

So @zanzio (zanzio) replied

    That group input node is just what you use inside a nodegroup, to configure the controls you can see outside the nodegroup. I wouldn't try to exactly recreate what he setup. His method is mostly the same as the one Acrivec showed you. You would just use a less saturated color of blue for the second diffuse node instead of white, and it will have the same result as plugging a diffuse into CarlG's nodegroup.

@Occultcg replied

    Omg… now i've tried it again and it seems i've missed something.
    
    It seems that it`s actually working with the second node. But it needs to have the same color and in order to make the reflection less visible, the color must be desaturated.
    
    Thanks, @zanzio for the heads-up!
    
    Thank you all for the help !

To which @CarlG (CarlG) replied

    Occultcg:
    
    > Can you please guide me ?
    
    See attached: cb.blend (1.3 MB)  
    Note that the slightly saturated blue you have is perceptually darker than the white you get from simply desaturating, so you need to tweak the brightness.

@CarlG (CarlG) replied

    Here cb.blend (1.4 MB) is a version that gets rid of the brightness control, but inside it attempts to keep the brightness of the original saturated color by re-building the color after bw conversion. Contains nested groups so it may be harder to understand. There are preview outputs if you want to check the difference between simply desaturating and rebuilding the new color at same intensity.

Then @Occultcg said

    @CarlG Wow, that is a complex nose setup! 
    
    I'm not into 2.8 yet but i have it installed and i can see the setups.  
    When i open the scene, it's opening 2 more Blender instances… weird.  
    Thank you for the node setups !

After which, @patnard added

    Nice bit of information. I'll keep that simple node setup in mind!

So @CarlG (CarlG) replied

    Occultcg:
    
    > that is a complex nose setup!
    
    patnard:
    
    > simple node setup
    
    Ok, I get it. My nose is complex and my nodes are simple 
    
    Desaturating using hue/saturation node makes full saturated blue (medium intensity) -> full white (full intensity).  
    Desaturating using BW node keeps the perceived intensity, but you have to rebuild the color. And I guess there may be other methods to do it.

@Occultcg replied

    Yes, thanks again!


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