i did a simple test scene to see how light can go through a window glass or transp
and the render is super noisy
is this normal ?
and how to correct this ?
now i tried up to 100 samples
and it is very noisy and also very slow !
thanks
What is your graphics card? Cycles and Blender can be modified with Nvidia cards to do amazing things. Unfortunately if you have AMD cards youre basically screwed unless something has happened recently. I have AMD, so im not sure exactly how to help. I believe if you go into your User Preferences and go to system, you can set options there and in the render tab set it to GPU.
“Sampled as light” background used? Any other light source exist (even with power=0 or black color)? Hard to tell looking only picture.
Instead of putting a lamp outside the window, put an emitting plane inside, right in front of the window. Make it invisible for the camera by unchecking camera in the Ray Visibility tab in Object Properties
I assume you thought you create a window, made of glass, with a glossy material.
That’s what you get and that’s why many renderers have the so called “portals” or why you simply listen to Sago and do what he tells you 
Cycles is supposed to do indirect lighting
so did a set up to test this effect!
i already know this trick for using an emission plane in window made transp
but thanks anyway
in this case the goal was to have an external light source going through a window
to get this feeling and look of a spot light through a window in a dark room
but seems that the noise level is very high and slow to render
what about this
“Sampled as light” background used
what differences does it do ?
can the number of bouce reduce noise may be?
and at what level of bounce should it be set ?
also i guess if you increase bounce level it will also take much longer to render!
and i did bring almost to 0 the sky light
thanks
did some other tests
i had an emission plane outside the room so i removed it
and noise whent down to almost 0!
how come one emission plane which is not adding light inside the room or almost add in render so much noise inside the room?
another thing i tested was to change the wall by adding some spec
and the more spec you add the less light there is in the room
is this normal or physically realist ?
thanks
First off, this is just how unidirectional path tracers work. Light coming through a glossy material through a small hole are going to converge slowly without bidirectional solving.
Second, there’s no such thing as ‘spec’ in a physically correct material system.
sorry can you elaborate on 2 points
spec in a physically correct material system.
all material have some form of spec and diffuse value!
what 's difference between uni and bidirec path tracer?
i will test again with glass and transp material
and see results
thanks
Ricky, you s aid you had it set to 100 samples, what about the passes? I have some projects i set that to 2000 for the light passes (i believe this is RENDER SAMPLES versus the VIEW samples).
That makes a HUGE difference!!!
good point
but the thng as i said is that in first test i had one spot light going through the window
but also left above the room on emission plane with very low energy ~ 0.1
but this gave a super noisy render
just did other test with no emission plane or other light sources in scene
and noise is almost 0
also did another test with indirect emission plane inside the room and noise is also 0
so it is strange that a small emission plane above the room create a siutation where the noise is very strong!
thanks
It is not strange, it is how PT in Cycles works, is sample one light source at a time, if you have only one you get almost BI like rendering because of “Direct light”, add 1 more light source (even if 0 color/strength) it will “pull” samples even if have low or zero energy. Cycles have no idea how you “ranks” lights, it is just plain list. There is possible optimisation, sample light using actual emission energy, i think is not that hard to do as current code already have algorithm that calculate pdf, you only need to adjust weight ad preprocess time. But it can be counter productive, you can have scene that main light is moderate, and strong light not need boost.
BTW, If you turn on “Sample as light” checkbox on World panel, it will add another light source that pull even more samples from main light source.
world panel !
i see only ambiant occlu checkbox
where is this other checkbox?
i can see the samples being distributed amonsgs all light sources
but in first test with simple case with one spot light to illuminate the room’s inside
and one plane emission well above which was not supposed to influence the inside of the room
but in this case the rendering was totaly super noisy like i had never seen before!
see first post pic
as soon as i remove the plane above room noisse = 0 !
i did another scene with only indirect emission light inside the room hiden inside box and
there was a little bit of noise but far from the first test i did!
so i find strange that an emission plane not directly lighting the room inside added so much noise in the render!
thanks
world panel !
i see only ambiant occlu checkbox
where is this other checkbox?
World->Settings->Sample as lamp checkbox, with grayed resolution field nearby.
and one plane emission well above which was not supposed to influence the inside of the room
but in this case the rendering was totaly super noisy like i had never seen before!
But it is. Read my post again.
i did another scene with only indirect emission light inside the room hiden inside box and
there was a little bit of noise but far from the first test i did!
Can you share that first .blend ? maybe something very obvious missed.
well i’v already modified the orginal file
i’ll try to redo it later this afternoon
and see if i get same weird noise!
i have another problem with the file
like when i move objects it moves in step of 1 BU
but i did not change any var in user so wondering what is causing this jerky move!
thanks
i tried to find the orignal set up
and could not redo it !
so let 's say problem solved!
thanks