[wow001]

We mainly render interiors and the present rendering a religious building with a stain glass window.

I have seen from other threads that small openings in rooms with sun light (environmental light) produces so much noise that the shot is almost unusable. We do not have the time or money to render them past SL 18/19 (30 hours on 8 core mac or 1 hour at ranchcomputing.com)

Turning the stain glass off so that there is just the window opening made the noise even worse and turning the sunlight off made for a beautiful clean image.

I do not think the client will be persuaded into a night shot!

What causes the noise when using the sun light in interior shots?

[tom]

As you say you've already seen this in other threads for so long, I'd like to start with the main question.

What causes the noise when using the sun light in interior shots?

A typical answer could be simple and short but my explanation will be a bit longer. As you know, we can classify illumination scenarios in two parts, direct and indirect. Direct illumination happens when a ray exits from the light source, bounces from a surface and reaches to the film without interacting elsewhere. This is a very easy task for any engine. However, the complexity begins when it doesn't reach to the film but keeps bouncing on other entities in the scene and further illuminating them. This is called indirect illumination. So, as the opening is small and the light is coming off from a distant/small source, it reduces the probability of filling the surfaces with light directly and so indirectly. Therefore, the engine needs more time to complete bounces and fill the room with light. The noise means, more computations are required for all these bounces have to happen. It's not uncommon in unbiased engines because, the biased solutions can do it faster with shortcuts but easily causing risk of introducing splotchy artifacts. It means, unbiased solution is expensive but it guarantees an absolutely correct solution. Of course, there are workarounds on user side for pushing up performance in these kind of scenes but I'd like to know more about your scene to make some suggestions here. I hope I could explain this matter.

[wow001]

Thanks for the explanation, it made it all clear and why external images are quicker.

I have followed the other threads and placed an emitter outside the window and turned off the environmental sun
Do you have any tips for making the emitter more like sun light?

Sun on SL12



Sun off SL12



Sun off with emitter behind window SL12

[tom]

It's the caustics from that window slowing down your render, not only sun or emitter. Could you turn off the other emitters and show only the illumination from window to find a good workaround?

[wow001]

emitter outside window only SL12

[tom]

OK, it looks like it doesn't badly require sun/emitter. I guess the window glass is not modeled in fractions but that's a transmittance texture, am I right? If so, please convert that texture to MXI,HDR or EXR and replace the window glass with an emitter using this texture. Therefore, hide whatever you have outside the window. I mean get rid of sun/emitter scenario behind glass. Because, it means you are converting the incoming light to caustics and it's naturally slowing it down.

[3dtrialpractice]

please convert that texture to MXI,HDR or EXR and replace the window glass with an emitter using this texture...

ohh ya.. brilliant.. esp since it is staind glass and you cant see outside..
Also for closer up pics showing glass in church.. if you want to get a supercool looking MXI/HDRI texture for the stained glass-if its a unique special to be created glass piece-(not so flat and have dynamic color and caustic pattens within it).. you can Make the stainded glass all modeled( really model out the glass and make it double sided or hollow boxish-use a displacment or sculpt in geometric deistorion) out in a seperate sceneand put the sun/emiter behind it- render it to a 32 bit image-maybe even with Dispertion ON if you have the time (render it striaght on w/ a camera with high focal lenght setting..200mm+ or so to preserve striaght lines of window-default camera of 35mm will lens distort it a bit) so and use that image to be the mxi/hdr emmiter in the church window..

if its staind glass that exist already.. go take a tripod and shoot 3-5 exposures of the window with a zoomedin lens and merge to hdri in photoshop (or hdr shop(free) to have a great real world stained glass emmiter.(you may want to use a plugin/app like "lens doctor" or "lens corrector pro" by richardrosenman http://www.richardrosenman.com/software/ to further straighten out edges of photos.

[knurrebusk]

This is my holy grail of render art, I can do all there is if given time, but not this without a renderfarm of huge size.
Wonder if the Human Eye is a better standard for Maxwell Render then a mortal camera.

The challenge is still there, I´ve done it in nr1(forgot the name of lightprobe creator) Lightwave/Lightscape/Max/Vray/MR/MR, it´s not easy is it?

But Maxwell push light, and do materials great so when Lightscape is dead long live the new king.
I´m a whore I know it, use 80% Autodesk products.

[wow001]

Thanks Tom and 3dtrialpractice.

Replacing the external sun with the a window mxi was an inspired suggestion.
I have not gone to the lengths suggested by 3dtrialpractice but with time I will give it a go.
We generated the stain glass window in illustrator and photoshop and turned that into an mxi.

There is a another stain glass window behind and windows around a dome in the top of the space.

Attached is the early tests (missing stone surround to windows and top stain glass panel) with only the one stain glass window.

You can see how clear of noise SL15 is.

Rendered to SL 12 maxwell 2.0




Rendered to SL 15 maxwell 2.0

[tom]

Cool! Now you can ctrl+del 2.0 executable

[wow001]

Is there an rule of thumb to the size of textures to size of application or is the rendering engine scale the texture before rending?

The MXI of the stain glass window is a photoshop file that is 79 mb in size (we have knocked it down to 11 mb), on the floor it is 15mb as we have done the floor in one piece so we could get slight variance in the tile colour.

[tom]

The engine will not change dimensions of your textures before or during the render. It's completely under the control of user so, you're responsible about supplying no more/no less than a suitable/necessary dimension for the purpose/viewing distance. Besides the dimensions, file size depends on file format you use but, the engine decompresses the image and the image allocates same raw amount of bytes in the memory independent of how small in bytes you've saved.