Big Sur cloud density

sriesch

I was messing around with clouds today, and I used the cloud from David Brinnen's cloud over Big Sur example scene as a material starting point. Due to differences when the material was used in my scene, I wanted to turn down the brightness a little bit. However, I noticed something odd that I don't understand why it is happening; In the Materials Lab if I lower the diffuse or ambient sliders or change the diffuse color to be darker, the cloud appears to become less dense, and I can see through it a lot more (rather than simply changing color). Why would this happen?

EDITED TO ADD MISSING SCREENSHOTS

David Brinnen

Sean Riesch said:

I was messing around with clouds today, and I used the cloud from David Brinnen's cloud over Big Sur example scene as a material starting point. Due to differences when the material was used in my scene, I wanted to turn down the brightness a little bit. However, I noticed something odd that I don't understand why it is happening; In the Materials Lab if I lower the diffuse or ambient sliders or change the diffuse color to be darker, the cloud appears to become less dense, and I can see through it a lot more (rather than simply changing color). Why would this happen?

EDITED TO ADD MISSING SCREENSHOTS

Er... not for me it does not. Lowering the diffusion just makes it darker, if it seems less dense, maybe it is an optical illusion in that the colour it is is looking closer to that of the sky behind. You could test this by changing the sky colour to something radical and trying different diffuse values. I used a bright orange sky (atmosphere off) to test.

sriesch

Ok, got a chance to test this better. David, if you still have that "transparency issue test.br7" file I just sent you for the other post in your trash bin, if you want (and you don't have to) you can use that directly to see what I'm seeing, just set the sky color to red, spot render a bit near the horizon line, then change the distant cloud material's Diffusion slider to about 18 and compare the difference.

In the attached screenshot, the original render on top shows the horizon line and sky nearly invisible behind the clouds on the right side of the render. The bottom render with diffusion at about 18 makes the horizon line suddenly visible almost the entire way across. I would have expected that white cloud to be darker grey with no significant change in the amount of red sky you can see through it, but instead it looks like it got very thin in addition to becoming darker?

David Brinnen

Sean Riesch said:

Ok, got a chance to test this better. David, if you still have that "transparency issue test.br7" file I just sent you for the other post in your trash bin, if you want (and you don't have to) you can use that directly to see what I'm seeing, just set the sky color to red, spot render a bit near the horizon line, then change the distant cloud material's Diffusion slider to about 18 and compare the difference.

In the attached screenshot, the original render on top shows the horizon line and sky nearly invisible behind the clouds on the right side of the render. The bottom render with diffusion at about 18 makes the horizon line suddenly visible almost the entire way across. I would have expected that white cloud to be darker grey with no significant change in the amount of red sky you can see through it, but instead it looks like it got very thin in addition to becoming darker?

Yes I can see what you mean. In basic shading the diffusion here is additive to the sky. So as you lower the diffusion you add less over the sky so the cloud becomes less visible. When you were talking about the density changing I was thinking you literally meant that lowering the diffusion was changing the material in the same way as changing the density property would. Which it does not. Lowering the diffusion will make the cloud appear "thinner" - but it will not affect the transition between cloud and not cloud as lowering the density would. Switch from basic shading to full shading to see the difference.