Sub-pixel mapping question

[cecofuli]

Hi,

I have one question. Universal setting is very useful, and my question is on Sub-pixel mapping

I know, this parameter must be OFF for correct behavior with LWF, but... the rendering time is very high if I turn OFF this option
See the attachment:

ON= 30 sec
OFF= 90 sec

And the difference from the two rendering is visible. I prefer when sub-pixel is off, but the time... mmm... 3X time!
Why that? there are some tips that I don't know?



Thanks!

[cecofuli]

And... Up

[Fekta.studio]

Hi, You may want look at here.: http://www.chaosgroup.com/forums/vbu...n-off-question
I asked the same question long ago and got some straight answer from Vlado.. Hope this helps..

[cecofuli]

The Vlado's reply is ok, but it's on Clamping stuff. And I know, if I trim the image with clamp option, RGB values are trimmed from 0 to 255 etc...
But in my test, in both image, the clamp output is OFF. Only sub-pixel mapping change from OFF to ON.
All the room is glossy shader (walls, windows, floor)

[Fekta.studio]

aaa yeah you are right I miss read
I think I read somewhere here about that too..

[jujubee]

Sub-pixel mapping - this option controls whether color mapping will be applied to the final image pixels, or to the individual sub-pixel samples. In older versions of VRay, this option was always assumed to be on, however its default value is now off as this produces more correct renderings, especially if you use the universal settings approach.

Keep in mind, the brighter an image, the longer the rendering times in general. Not sure if that really answers your question however. As to why one is brighter and the other is not, I guess that's a question for Vlado.

If you lowered your camera exposure to try to match the darker image, what times do you get?

[themaxxer]

@ cecofuli
it's funny to read such a question from the maker of the vray complete guide. it's my favorite book!
are there plans to fit all features of vray 2?

best regards
themaxxer

[vlado]

And the difference from the two rendering is visible. I prefer when sub-pixel is off, but the time... mmm... 3X time!
Why that? there are some tips that I don't know?

The subpixel mapping kills some of the brighter samples, which makes the job of the image sampler easier. That's why it renders faster, but the result may be somewhat incorrect (depending on how much the clipped samples contribute to the result).

Best regards,
Vlado

[cecofuli]

hi Vlado,
thanks. Also I found this, write by you some time ago:

"The "Sub-pixel mapping" option for V-Ray does exactly that - it determines whether color mapping (along with clamping) happens before (on) or after (off) the filtering for anitaliasing"
So depends of the scene, the Sub-pixel can slow down the rendering time and the brightness.
I think I can't do nothing to speed-upe the rendering time in my interior scene, with Sub-pixel mapping OFF.