noisy windows in cycles

if i render a window with glass + Transp
and my object has a mirror or not
i get a very noisy windows render

did test with only simple mat over each other and does not do that !

what could do this noise and how to remove it ?


You just need to give the image more samples, even a transparent material will still take time to render because the ray has to be evaluated when it hits the surface.

ok but on the left i did a test wiht plane glass over green mat and it does not make noise

only in the cabin is it doing this !

why in one location and not the other ?


A close look seems to reveal that the light going into the cabin is actually transmitting through two surfaces with opposite facing normals instead of just one (looking at all of the reflections within that makes the cabin seem out of focus).

The fact that you would have opposite facing normals also would make the glass component behave a little more like actual glass (since a window is a volume), so you would have more evaluation, more refraction/reflection effects, and this more noise as more complex effects require a higher number of samples.

i did apply a solidify on 1/2 the cabin
so it did also add a second window layer
but it was more unintended !
but normals inside walls are inward so should be ok !

so i remove the double layer glass
and render again at 100 samples is still very noisy


It’s actually not as noisy as it used to be when you directly compare the two images.

The final source of noise I can think of by now would be the indirect lighting inside of the cabin, the reason why you don’t have noise elsewhere is because every other piece of geometry is receiving direct light from either the light or the environment.

well light inside has to go though the glass then
it becomes the little monster noisy render for these areas

so is there some setting to reduce this kind of noise!


You can try clamping the samples to a low value, but you will see your image robbed of much of its dynamic range as a result (if you have any bright spots in the image).

You can also try turning up the ‘filter glossy’ option if you have a significant amount of glossy materials and/or caustic paths in the scene, but I’m not sure if it will help that much here.

The final option is to just render it with more samples, a scene this simple shouldn’t take all that long to accumulate a large amount of samples unless you have a weak PC (lower-powered than the average i3 dualcore machine)

just did atest with a lamp inside
and still noisy

for now don’t really want to get much higher then 200 samples
takes too long to render like 1/2 hour at least!
sorry still with old PC and vista 32 bits so it is slow
probably equivalent to I3 i guess

hope to get new PC soon !


A new lamp isn’t going to help in this case because its energy will be added on top of the noise inside of the car, the noise will be brighter, but it won’t be less visible.

For a new lamp to help, you would need to use lightpaths to make the glass opaque to lamps so the only thing lighting the inside is the interior lamp.

Have you tried setting your minimum transparency samples equal to your maximum this removes some stochastic (if you use that term here) noise. I suspect it will improve render without much of a time hit.

it is already equal!

fond something here seems to be cause by caustic
if i remover it noise is a lot less but much darker !


If you dont mind cheating a littel with the glass effects, you can set up a glass material that uses transparent instead of glass when it hits a diffuse surface. This will reduce a lot of the noise.

Here is an example with a green plane inside a glass cube. To the right you see a pure glass material and to the left you see a glass material that act as a transparent material when it hits a diffuse material.

ok did test with lightpat diffuse
and it does reduce noise a lot
by my green mat is like a composite diff + glossy
so would this change the glossy render on the outside also ?

now i may have to redo thsi model almost from scratch cause i forgot to add double layer for this green mat and cannot really add solidify to it or all the other parts will become mess up!


You can quickly make a little change so that it also handles the glossy of your material.
I have done a little change in that i now use the “is single ray” option and then switch the input.

It will not change how your green material is seen outside of the windows. It will only change how materials with more then one type of ray will see the glass, and not how you will see the materials.

there is a good tutorial about this here:

did a new test here seems to reduce noise if there is only one glass layer
if you have double layer glass then it does not really work as well!

but nice trick i’ll keep it in mind for single layer glass


You may just want to change the “is diffuse ray” to “is reflection ray” to avoid conflicts with the reflection of the glass.