10-07-2020, 08:40 PM
(This post was last modified: 10-07-2020, 09:37 PM by sciroccorics.)
Hi Micheus,
Nice trick what you propose to deal with area lights, your rendering of the ceiling is much closer to the result obtained by Yafaray. I'm going to try this on other scenes.
Good idea to check the exported POV file to see if everything is correct, didn't thought about that. I found a bit strange that the exported gamma value used by Povray is 1.0 instead of 2.2, because the final Povray rendering in quite close in overall luminosity to the Yarafay rendering which uses this same 2.2 value for gamma. So I made some additional tests and discovered something really strange: in Yafaray when increasing the gamma value, the image look brighter (which is the usual behavior when performing the same action in image processing softwares), but when increasing the "assumed_gamma" parameter in the Pov-Ray file, the image looks more and more darker
For instance, putting a gamma to 10 gives an almost black image in PovRay, and very overexposed picture in Yafaray.
So I checked PovRay documentation, and especially the "2.3.4 Gamma Handling" section of the reference manual. I didn't made all the calibration experiments suggested in that section, but I understand that the "assumed gamma" used in Povray is actually the gamma value that is expected for the visualization display, so PovRay tries to COMPENSATE the non-linearity provided by the device, which means that it darkens the image for high gamma and brightens the image for low gamma. So this is the opposite behavior done by Yafaray.
Hi oort,
Yes, the ambient light was set to zero both for Povray and Yafaray, I only put a non-zero value in Wings to avoid a very dark rendering by OpenGL. I did that on purpose, because the Cornell box is supposed to be only illuminated by the ceiling light, in order to check whether the interreflections are correctly computed.
I guess that the difference in speed that I observed between both renderers are coming from non-consistent parameter settings I did. For instance, PovRay allows one to control the number of specific photons used for caustics (so called "media photons"), in addition to the total number of photons, while Yafaray only provides a single global number. Also the number of samples used for area light sampling is fixed in Yafaray (on the "Yafaray" tab of the Light properties), while it is adaptative in PovRay, which may explain the speed difference that you have noticed when including area lights with Yarafay.
As I said in my first post, the images provided by Yafaray appear more realistic than the ones provided by Povray. I also find the Material and Light parameters more "intuitive" in Yafaray (well, it's still complicated to get expected effects without any experimental testing). But on the other hand, it's not clear how to choose between the "photon mapping", "path tracing", "bidirectional tracing" or "stochastic progressive photon mapping" options in the "Lighting" tab of the plugin window. Even if I understand (a little bit, at least) the algorithmic differences between these techniques, I'm not sure when one should favor one techniques instead of another for a specific scene to be rendered.
Nice trick what you propose to deal with area lights, your rendering of the ceiling is much closer to the result obtained by Yafaray. I'm going to try this on other scenes.
Quote:The gamma settings has been exported with a constant value of 1.0 although the Render dialog show us 2.2
Good idea to check the exported POV file to see if everything is correct, didn't thought about that. I found a bit strange that the exported gamma value used by Povray is 1.0 instead of 2.2, because the final Povray rendering in quite close in overall luminosity to the Yarafay rendering which uses this same 2.2 value for gamma. So I made some additional tests and discovered something really strange: in Yafaray when increasing the gamma value, the image look brighter (which is the usual behavior when performing the same action in image processing softwares), but when increasing the "assumed_gamma" parameter in the Pov-Ray file, the image looks more and more darker
For instance, putting a gamma to 10 gives an almost black image in PovRay, and very overexposed picture in Yafaray.So I checked PovRay documentation, and especially the "2.3.4 Gamma Handling" section of the reference manual. I didn't made all the calibration experiments suggested in that section, but I understand that the "assumed gamma" used in Povray is actually the gamma value that is expected for the visualization display, so PovRay tries to COMPENSATE the non-linearity provided by the device, which means that it darkens the image for high gamma and brightens the image for low gamma. So this is the opposite behavior done by Yafaray.
Hi oort,
Yes, the ambient light was set to zero both for Povray and Yafaray, I only put a non-zero value in Wings to avoid a very dark rendering by OpenGL. I did that on purpose, because the Cornell box is supposed to be only illuminated by the ceiling light, in order to check whether the interreflections are correctly computed.
I guess that the difference in speed that I observed between both renderers are coming from non-consistent parameter settings I did. For instance, PovRay allows one to control the number of specific photons used for caustics (so called "media photons"), in addition to the total number of photons, while Yafaray only provides a single global number. Also the number of samples used for area light sampling is fixed in Yafaray (on the "Yafaray" tab of the Light properties), while it is adaptative in PovRay, which may explain the speed difference that you have noticed when including area lights with Yarafay.
As I said in my first post, the images provided by Yafaray appear more realistic than the ones provided by Povray. I also find the Material and Light parameters more "intuitive" in Yafaray (well, it's still complicated to get expected effects without any experimental testing). But on the other hand, it's not clear how to choose between the "photon mapping", "path tracing", "bidirectional tracing" or "stochastic progressive photon mapping" options in the "Lighting" tab of the plugin window. Even if I understand (a little bit, at least) the algorithmic differences between these techniques, I'm not sure when one should favor one techniques instead of another for a specific scene to be rendered.
>>> sciroccorics <<<