How can I remove these white leaks in corners and contacts?
This is Micropolygon render, Irr settings does not help, neither raising AO samples, nor changing Raytracing bias.

http://screencast.com/t/WYMTWKWKqj [screencast.com]

I remember having similar sorts of probelms with a different raycasting shader. The only thing that completely eliminated them was changing to raytrace renderer. IIRC, upping the shading rate helped, though. (OBJ -> Shading Quality)

Thanks, yeah upping shading rate helps a bit, but still can not eliminate it entirely.

this looks like ray bias
most probably but not necessarily Raytracing Bias parameter on mantra, since you are saying it has no effect

what do you use for AO?
if envvight in AO mode or GI light shader then Raytracing Bias property should work, but mantra will use rendering property at the the lowest level so if the mantra setting has no effect, have a look on cam/object/material/… if there is Raytracing Bias property added

but if you are using occlusion shader, AO material, then it has it's own bias setting

but the fastest solution is always to post here your scene and spare us from guessing

Unfortunately I did not save that scene, it was really just cube with opening and sphere, and env light. But yes I am using AO with environment light. I noticed that changing bias to higher value like 0.1 I get these leaks even larger. Changing it to smaller values does not make any visible difference.

However I tried same approach in another more complex and bigger scene and I did not experience such leaks. As you can see here http://screencast.com/t/fArben9g [screencast.com] . Might be because of scene scale?

Hi,
There a few things that will help. For a flat wall you will need to increase the shading quality on the dicing tab try 2 or 3 and that should get rid of those artifacts in the corners. As per the image below.




Next you can tweek some of the parameter and make sure you are set up for rendering and viewing on a monitor without a LUT. which will normally have a gamma of 2.2 .
From the Houdini menu Edit > Color settings > Color Correction set the gamma to 2.2 and check on all the options. Then in your mantra ROP >shading Tab > colour space > set to gamma 2.2 . Why ? Read this from a question I asked http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=26487&highlight=gamma+2.2 [sidefx.com] . Which Tomas kindly answered in great detail.

It is true on large scene scales the ray bias settings will need changing I think of it as a multiplier from the base Houdini settings of 1 unit = 1 meter. So if your building comes in from another application where 1 unit = 10cm you are certainly going to need to be increasing that ray bias.

See the attached scene that uses a take to switch between using a AO shader and the env light. I will say straight off the bat that I like to have my AO controlled in my shader .

Rob