Repeatability question

[TSPCo]

Attached are 4 renders using the same settings. When I say same, here is what I did render, close, render close. I never changed anything. But these four scenes are different.

[derei]

try higher preset (easy8) or better try progressive ! ... progressive will give same result every time.

[Chris]

What preset are you using? Unbiased presets are designed to converge on a "solution" which means they will steadily approach uniformity but in the early stages, you are going to get some variation between images. Biased presets are generally repeatable, but if you are using a low preset you may see light "flares" or "leaks" caused by approximation errors. Looking at your image, you are getting light flares in random locations, probably because you are using a low preset (and probably because you aren't using "solid" models; single surface walls suffer more often from light flares).

Ultimately, renders are based on random numbers so there is always some element of variation (though your example is pretty extreme). That is why Twilight provides the ability to "lock" the light cache when doing camera animations; it prevents the lighting from changing between renders.

[Fletch]

Subject: Reflective anomalies

If you see sparkles or light flares in quick render settings, don't worry, this is due to the low light sampling in quick render settings.

Subject: Easy 1-7 Photon Mapping and Final Gather (Biased)

For those wishing to make changes to the Easy Settings 1-7, they will need to understand as much as they can about what Photon Mapping and Final Gathering is, and how it works with Twilight.

Easy1-7_rendersettings.jpg

First, let's discuss in general about the Easy Settings 1-7...

Here's a very rough basic how this rendering thing works...

Each light randomly shoots out "photons" these are basically vectors of light that are traced for a certain number of bounces to their final destination, the camera.
If you use progressive rendering settings (Easy 8, 9 or 10) they use different algorithms to calculate every bounce of light. Each has it's strength, so they are named for that strength.
If you use non-progressve (biased) Easy 1-7 render settings then not every little bounce of light is calculated, some of the light is interpolated and the amount of photon rays per light source are controlled within the render setting. The fewer the photons, the more interpolation needs to be done. The faster the rendering will calculate. So the Easy 1,2,3 render settings are quick, but they have few photons, and a lot of interpolation. This is why they are quick and why you see light blotches, splotches, flares, sparkles, reflections, whatever you want to call them. This is because there are few photons being calculated, and large surface areas are being interpolated between where each photon lands.

In a scene with a lot of direct light, this is NOT a problem. There are lots of photons per light, so there is more overlap where each photon will be landing near to another photon, so the calculation will be less unpredictable.
In a scene where there is only sun and sky, but you are looking at the interior, there will be a massive difference between each rendering, because the photons are shot from the sun and sky toward your windows on your model. If those random photons happen to make it in through one of the fenestration openings, then it will possibly bounce around the space and end up hitting the camera.

So, if you render a dark interior, lit only with Sun and Sky, you must use a high render setting to get decent results. The lower settings basically will tell you if light is coming in the window or not, but that's about it. That's nice, it will render very fast, but it is just a quick preview. It says specifically in the name of the render setting what result you should expect. If you want low quality, use low quality, if you want high quality, use high quality.

Now, there's one key thing that makes a big difference, if you were to cover each window with a sky portal, then it tells Twilight "hey, sun and sky photons, I want you ALL to come through here, ok?" So then you should use Sky Portals, and you can then use even Easy 02 to get good lighting results with such low lighting/low number of photons. They work even better when combined with Easy 09, where all the light coming through will help. But be careful to read thoroughly about Sky Portals, as they are not a cure-all, and have some caveats to their usage. Here's the best thread including video tutorials:
Subject: Sky Portal Material Library for Twilight Render

[TSPCo]

Thanks guys, I was curious how it works.