Cornell box comparison : PovRay vs. YafaRay vs. Kerkythea

[micheus]

- I could not manage to get the area light visible as a white square in PovRay, as it can be done in YafaRay be defining an objet with "Light Material", so the ceiling is not very nicely rendered with PovRay

POVRay doesn't render its lights.

Your ceiling light is the entire object and not only the bottom face. So, what we need to do in this case is to create a mesh light. We select the object we want to be turned into light and in the context menu choose Object to Area Light.

In some cases, if we want to put the light only on the bottom face we can use the plane light "replacing" that part of the light - like in this image bellow, from the old post at the plugin development.
The piece that should be used as light source received a material with emission set to 1.0 and the area light is put in front on it:

In that thread there is also a tip for SSS, size influencing shadows from area light and quality setting comparison.

I tweaked the exported files in order to change:
- 'gamma 1.8' and 'count 1000000' in global settings; [bug]
- Light area colour from 0.5 to 1.0, matrix light 20x20 and added 'orient';
- add the 'emission 1.0' to ceiling light material (panel object); [bug]

Left: bottom and side faces of panel with the emitter material;
Right: only the bottom. The area light was placed just bellow the bottom face (not over).


The panel was turned in a area light.

- The R/G/B color walls appear as very uniformly colored in PovRay, while there is some gradient in YafaRay which seems more correct. On the other hand, the color is a bit "saturated" in YafaRay and show a visible circle on each wall, which is not very realistic

I agree about both observation.
But, by considering a flat light on ceiling I think it can be more natural to see a homogeneous lighting them a rounded one which looks like the source of light is a spot or point light.

However, I noticed some issues with the exported .POV file:
- Emission for material property isn't exported;
- The gamma settings has been exported with a constant value of 1.0 although the Render dialog show us 2.2 (a good value usually is around 1.8-2.2);

I will have to take a look on the exporter again.

- The glass lens looks much more convincing in YafaRay that in PovRay (altough I use the parameters of the "glass" material from the PovRay material library, and the same index of refraction for both plugins)

Yeah. It looks like let it reflect full white isn't a good approach in this case. In the image I put above you may noticed it looks a little better. I disabled the Extended Interior settings (we most the time need to only set the IOR) and the reflection minimum colour to <178,178,178> (0.7).

- Similarly, the boxes appears as more glossy in YafaRay images than in PovRay ones, though the same specular exponent (50) is used for both plugins

Try to find the settings to make two different engines produce the same result is almost impossible. I already tried that.

- A strange arfefact is visible in the PovRay images on the bottom corner of the horizontal box

Indeed. I could figured what is that. Would need to spend more time to understand what is that.

- And finally (maybe the most important), on my computer PovRay computations are about 2 to 5 five times faster that the same image in YafaRay, while YafaRay is usually known to be a "fast" engine. So maybe am I wrong with some of my settings on both plugins.

That is possible.
You can slow it down if you increase photons count to 1000000; increase the area light matrix in order to get a smoother shadow;


I noticed you choose to render a squared image. In cases like this, where the screen we are working may not have the aspect ratio we are going to use for rendering its possible to use a camera feature which allow us to see on screen the area which will be render and then we can better arrange the camera in the scene. First you access the camera settings and choose the ratio. Then, in the View->Show menu enable the Camera Image Plane: