I have a general question about the Exposure color correction in the Vray physical camera…
Are there any negatives to having this turned off? I understand that it is completely taking the “physical” out of the Vray Physical Camera, but if you want a perfectly exposed image, wouldn’t turning this off make sense?
In my current situation I find myself needing to render products on a white background. So I’m overriding the Environment to 255,255,255 complete white. I then find myself tweaking the ISO with each shutter speed / F-number change of the camera to maintain that complete white background as the Exposure color correction affects the BG override.
I’m just wondering if there is anything I’m over-looking in turning it off. Many thanks.
It isn’t that uncommon to find a workflow that doesn’t use camera exposure… The workflow that best solves your problem is the correct workflow to use.
Years ago there was a mathematical equation that helped you click a color in your scene and enter the RGB into a formula which if memory serves output the white balance RGB and ISO number that you needed to render the color you clicked the near exact RGB value you want it to be. Not sure if it is still valid. A search of the archives would probably lead to several threads on the subject.
That said… A perfectly exposed image is highly subjective in the world of 3d.
I had to go way back to dig this up… ;). This is from 2007 so I am not sure it is still valid but it may work.
Originally Posted by Vlado
I had to deal with this recently, so I thought it may be useful.
The problem:
We want to obtain an exact RGB value for some (small) surface in our image. Let’s say the RGB value is xr, xg, xb which range from 0 to 255.
The solution:
1) Render the scene in any way you want with any settings you want, but make sure you use Linear color mapping with 1.0 for both Bright and Dark multipliers and the “Clamp output” option is off, and you are using the V-Ray camera “Exposure” setting. It would also be handy if you render to the V-Ray VFB.
2) Measure the RGB value at the pixel you need to match. If the values are, let’s say (pr, pg, pb) again from 0 to 255, adjust the V-Ray camera “White balance” to be (pr*255/xr, pg*255/xg, pb*255/xb) and multiply the camera ISO setting by (xr+xg+xb)/(pr+pg+pb).
Note that this works only for Linear color mapping. In principle it can be done for any color mapping, but the numbers are hard to find by hand.
Very cool crazy homeless guy. Thank you for digging that up! You are right about exposure being subjective. I guess what I should of said is limiting variables of exposure. I’ll play around with that equation though for sure! Thanks again.
If the reason behind the choice of using exposure is to match a photographic plate, then I suggest to stay away from physical camera, or avoid the exposure settings and go by matching the light value by eye. The reason being that you can’t never match 100% of the exposure from a photo with those numbers (unless you are trying to match plates filmed with cinema lenses where there are less variables to consider). If you want to have a photographic/cinematic approach to the creation of your images that has a more realistic relation between exposure/depth of field/motion blur and be able to have creative control over your images, or to create/match lens distortion, then physical camera is a great tool.
the only drawback is that you lose white balance control in vray cam.
but I find it easier to work like that in interior scenes with complex artificial lighting - its easier to manage intensities - light value of 5 will give you the same pixel value when rendered.
and if you need white balance control - use automatic exposure control from max’s environment - it will not affect the background if you don’t want it to.
thing to remember - black vray environment override - it will prevent white max background from interfering with your lighting in some cases.
Nice information. Thanks guys. Using Maya (should of specified), but pretty much the same thing for the most part.
I think I’ll keep exposure control turned off for standard on white product renders and keep it flicked on for beauty renders. I have years of background in real estate photography so using the vray physical camera like a real world camera feels natural. Just trying to streamline some of our production stuff.
With names like, “sharktacos” and “Crazy Homeless Guy”, I’m feeling a bit of regret for choosing such a bland name… Thanks guys for making me feel inadequate. Haha.
