GUI - FG tab
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FG tab
Here is where you will spend most of the time in Kray GUI. This tab controls the most important stage of rendering – final gathering (FG).
GI resolution
See GI Resolution for more information.
FG preset
This selection list lets you choose predefined FG preset. When you choose Custom from the preset list advanced settings are unlocked.
FG threshold, min rays, max rays
Whenever you see threshold in Kray interface it always means the same.
Kray starts sampling point by shooting min number of rays into the scene. Threshold defines the how much difference between two pixels is "allowed". If difference is greater than that defined by threshold, Kray will increase rays, until the difference gets smaller than the threshold. It will also stop adding rays if it reaches max rays before reaching the threshold value.
The FG threshold should be usually left at default 0.0001. Increasing this number may cause splotches in the scene but may reduce render time.
Min rays define the least amount of rays each sampled point will fire. This value is usually kept low – around 100-300, but may be increased if there are artifacts in the scene that do not disappear when increasing max rays value.
Max is the maximum rays Kray will use for any sampled point. If this value is too low you splotches will appear. Increasing this value means longer render time. By increasing this number render time increases approximately linear. For example if you increase max rays from 500 to 1000 render time will double.
Prerender
Prerender is the first step of FG which helps in defining which parts of the scene should be evaluated more thoroughly. When prerender value is 50% it means that it will render use 50% of the final resolution. You should also note that increasing prerender will cause longer prerender pass but shorter final render pass.
This value is best kept between 50%-100%.
- It is important to understand how Kray chooses location of samples. To optimize rendering as much as possible samples are placed at “strategical” places. This are usually places where surfaces are close to each other or places of sudden light change. On large flat areas there is no need to compute samples for every pixel so Kray will only place only very few samples there. This way speed of rendering can be greatly improved. More samples means longer render time. Therefore it's important to find the right balance between sample density and render quality.'
There are several settings which control placement of samples in a scene:
Spatial tolerance
[needs more info from G]
Angle tolerance
Angle tolerance defines the placement of sample points on curved surfaces. The value defines how much can surface angle change before new sample is added.
Distance min / distance max
[needs more info from G]
B/D
Brightness/Density will add more samples in places of high light contrast.
[needs more info from G]
Blur
Will blur neighbouring samples and thus reduce artefacts such as splotches. The drawback is that it may also blur some very fine indirect shadows.
Show samples
This option lets you visualize placement of FG samples. This is primarily used for testing and troubleshooting.
Off
Will not show any samples.
Corners
Will show only samples in corners.
All
Will show all samples in scene.
FG reflections
Will turn on or off tracing of FG rays on reflective surfaces. Turning this option off may speed up render times but it may also cause inaccurate reflections.
FG transparency/refractions
Will turn on or off tracing of FG rays on refractive or transparent surfaces. Turning this option off may speed up render times but it may also cause inaccurate calculation of GI through transparent/refractive surfaces.
- Warning* Your windows may block FG rays if you turn this flag off. To work around put them on a separate layer and turn ON "unseen by radiostiy" in the object properties.
Corner distance/Paths
When Paths is set to > 0 Kray will turn to path tracing when rendering corners. This may reduce splotches or light leaks. Distance specify how far from a corner paths rendering will be used.
