Exposure Compensation & Highlight Compression

[ringas]

Hi,

Are there any guidelines to setting those?

When using Vray, I had gone through a detailed metering procedure, using grey, non-reflective materials and setting the camera's ISO and speed so that the value of the rendered image at the brightest spot is similar to the value of the diffuse component of the material. Once I got close enough, I started using those values as a starting point for the cameras. I am pretty happy with the results and haven't changed anything for a couple of years.

Now, I think there isn't a specific Corona Camera, where I could do something similar (I wish that we have one someday).

I could just not mess with anything and do heavy post in Nuke using full float EXRs, but it would be nice to have a starting point.

Any thoughts?

Tassos Ringas

[Ludvik Koutny]

Exposure compensation is a basic brightness of your image, it does same thing as changing shutter, ISO or F/stop values in Vray. It is temporary solution, and it works similar to simple exposure compensation function found for example in digital cameras or cell phone cameras. You can go in both positive and negative direction, so to get a good brightness in strong exterior daylight, you might need to set Exposure compensation to somewhere like -1 to -2.

Highlight compression is similar to Reinhard tone mapping in Vray, with only difference that it goes in opposite direction. Increasing HL compression value will reduce burn areas on your image, while in Vray, reducing burn value in reinhard does the same thing. So you just keep increasing this value until you reduce highlight burn as much as you desire. Sometimes you might need to go really high, for example up to 50 :)

[Ondra]

This is purely artistic issue, there is no "correct" settings that would for example be more physically correct or render faster. So just use your artistic eye to find the settings you like. I would start with the exposure compensation to set the overall image brightness, and then use highlight burn to reduce overexposed areas. Since it updates in real time, you should have no problems finding settings you like.

[ecximer]

I completely agree with Rawalanche and Keymaster. I don't see any problems in Corone with Color Mapping. And here in Vray just there were continuous dances with a tambourine what to find good balance of a treatment of light and shade.

[maru]

I think what Ringas meant is some kind of real world reference to scene's overall brightness. Easiest way to do this would be using real units for lights' power. In current version of Corona you can illuminate your room with lights with brightness of 0.5 and adjust the exposure controls to make it look good and you can use lights with power of 5000 and adjust exposure controls as well but there should be some reference value (like brightness of a 50W light bulb or power of sun) so that you know whether to set brightness to 0.5 or 5000.

[ringas]

Thank you all for the replies!!!

Maru, this is exactly what I meant, but it's not really a problem as I am always grading in half-float in Nuke.

Coming from a photography and architecture background, what I have found during all these years of using advanced rendering programs is that they are so well designed that I can apply my old and trusted "Sunny 16" rule and I am always getting what I expect. It would be nice to be able to do the same thing in Corona sometime, I know we are half way there, as there is already an aperture setting used for DOF, so it now misses ISO and speed...

This is so exciting, reminds me of the thrill of the early Ghost days, when we used to shape what actually became Brazil!!!

Happy to be on board and kudos to you all :)

Tassos Ringas