Exposure - RT vs. production

[palibebeh]

Hi!

I'm playing around with RT, and so far it's a great tool.
Theres much room for improvement, but what are updates for right?

Now the problem is this:
I have a small test scene - a morris mini model on an invisible plane, lit entirely by a hdr map.
And while in RT all looks fine, in the production render the reflections seem to be much much too bright, effectively burning the entire picture. Same goes for the background, which is the same hdr map but thrown into an output modifier - in RT it was way to dark.
You can cealrly see in the attached pictures that RT/prod are not the same - and they should be.

Am I doing something wrong?
No lights, just IBL, vrayphyscam, irr+bruteforce.

RT


PROD



also - i found that this issue has already been discussed, but no definite answer/fix was given.

[vlado]

Do you have the "Legacy sun/sky models" option on or off in the V-Ray Global switches rollout?

Best regards,
Vlado

[palibebeh]

i'm not at the office at the moment, but the scene was made from scratch in 1.5 sp3a.
the car model was imported from a 3ds file, and other than that everything else is default - so legacy sun/sky model should be set to off.
but as i said - there are no lights in the scene, especialy no sun/sky only one hdr map for illumination and reflections.
i'll check this first thing in the morning, but assuming that the 'legacy sun/sky' is off - what else could be the problem?

[vlado]

i'll check this first thing in the morning, but assuming that the 'legacy sun/sky' is off - what else could be the problem?

I'm not quite sure; if you get me the scene, however simple, to vlado@chaosgroup.com I will be able to tell you more.

Best regards,
Vlado

[simmsimaging]

Something to try/check: If you are using the Max bitmap loader for your HDRI make sure to override the gamma on loading to 1.0

Vray seems to do it anyway but RT does not and it has given me exposure variations before. If you use Vray HDRI to load instead it matches every time.

[palibebeh]

@Vlado - 'legacy sky/sun' is off, I'm preparing the scene and will send it to You asap.


@simmsimaging - thanks for the tip, but i'm using vrayhdri so that's not the issue.


what i found today is that there was one light in the scene - vraydomelight - with the hdr image as a texture. but when i turned it off, it had NO effect on the RT window - as if it wasn't there in the first place.
BUT when i turned it on again - the light was included in the RT calculations.

also what's strange - i locked the render buffer in RT settings, but when i switched to perspective view in max, RT started to calculate the image without any exposure (thus veeery bright and burned) - just what one would expect from a rendering without a vrayphyscam, but from a physcam point of view...

[tecsun]

Hi Palibebeh, try increase the Ray Per Pixel under Performance to 32.

I have the same problem that RT exposure is perfect but production render is seriously blown out. After increasing the Ray Per Pixel, it looks better but still not same.

[tecsun]

Hi Vlado -
As I mentioned above, by using "4" for Ray Per Pixel, RT result will appear alright when it started, but very soon as the quality getting better the exposure will be automatically corrected (and the result is nice), while 32 will give much better result (but still not accurate) but slower performace. Increasing Trace GI Depth to 100 doesn't help too. Please see attached image for better idea.

So how does this happen? Thanks.

[Pixelab]

also what's strange - i locked the render buffer in RT settings, but when i switched to perspective view in max, RT started to calculate the image without any exposure (thus veeery bright and burned) - just what one would expect from a rendering without a vrayphyscam, but from a physcam point of view...

I had recently the same problem, seems that RT takes the point of view without taking the exposure into account. Changing the exposure to approx f/2 and 1/40s did match both results (but I had to dim down all the lights and HDRI in the scene)