Noisy specular with gradient ramp as a normal map

[tricky]

I am rendering a metal walled building that has a profile to the metal surface. Normally, we model the profile (something like half-round or trapezoidal profiles like on your typical warehouse). However, for time saving reasons (aka crazy deadline!), I am trying my luck with a normal map to fake the undulations.

It's a very simple VRay material with a grey diffuse, mid-grey raytrace with glossiness at 0.85. In the bump slot I have a VRayColorToBump and in that I have a Gradient Ramp map with a linear gradient to simulate the profile of the cladding.

Where the cladding is reasonably close to the camera, it looks fine. Mid distance, I am getting a VERY noisy specular. GI etc is basic, but it all looks clean.

Any solutions to stop all this noise? My settings are pretty much the default: Bucket rendering, Min/Max: 1/24, Noise threshold 0.005.

Here are a few images to explain. Any solutions to remove this noise? It will be a nightmare with animation!

[Morbid Angel]

If I read your post correctly you can't use black and white ramp as a normal map. Normal requires XYZ with a neutral color. Perhaps its another case, possible to post this piece of geo + lighting here for evaluation?

[tricky]

I thought that plugging the ramp into a VRayColorToBump would get around this. Attached is a bit of my scene. It's Max2016.

[tricky]

I've also tried creating a 'genuine' normal map from some profiled geometry, but I get the same results - long render times on these 'speckly' areas. Any suggestions?

[Morbid Angel]

Hey Tricky,

So I saw that your color to bump was set to 1000 mm? if your scene is to scale that means the bump of the ridges is 1 meter high? If I set it to something lower, the spec renders fine. I think its totally related to the fact that the bump normal has been pushed beyond its designed angle I ended up blurring the gradient by 1.1. I did not use color to bump, since gradient is grey anyway I just plugged in the ramp directly to bump with value of 10 instead of 100.

[tricky]

Thanks Dmitry - I must admit, I just left the default value for the colour to bump - I didn't check that it was 1000mm!

How does that relate to the bump value - any ideas? The reality is that this profile would be around 40mm high, so, to achieve that, would I set the colour to bump to 40mm and the bump value to 100? (assuming I stuck with the colour to bump map that is)

[tricky]

...my logic is that a normal map will achieve 'better' results (more defined?) than a bump map alone. I have generated the attached normal map from an actual profile. How would I construct a material where the normal map would simulate a profile depth of 40mm?

(this is a 1m x 1m panel)

[Morbid Angel]

I don't think you can accurately replicate that, after all normal map or bump map is a cheat / fake. It just bends the normals of underlying geometry to approximate look. What you can do though is use 2d displacement with actual height and get a value of 40 mm, then eyeball whatever that would be in bump/normal.
I think the best way to make the normal map is to model the geometry and render it to a normal map texture - is that how you did it?

[Morbid Angel]

Here I used the normal map you posted and plugged it through the vrayNormalMap node into bump. Set the bump to 100 in the vray material, then set the normal map to 0.4 which seems to give a decent amount of detail.

[tricky]

Thanks. I got a similar result, but it just doesn't look quite right to me - there seem to be too many fine horizontal lines. Know what I mean?

(and yes, it was created from actual correctly sized geometry)

[Morbid Angel]

I think its just the nature of pixels and angled lines along with filtering. If you render that larger it would be better. Additionally how the texture is being filtered is also important. If you change filtering method to summed area from pyramidal it will be much better. You can also use vray hdr loader and play with the filtering options there. Its a fine balance, bump never really works as well as real thing it looks different at different distances etc etc. Here is the result at double hd and summed area filter. I also raised the lanczos filter to 3.

[dlparisi]

I think the best way to make the normal map is to model the geometry and render it to a normal map texture - is that how you did it?

Agreed. This has worked well in the past for me.

For a little more detail what about just a quick 2D VrayDispMod? You can keep the 2D mapping resolution quite low too since its a pretty simple texture. It shouldn't add that much time to the renders, right?