Chaos Corona Forum
Chaos Corona for 3ds Max => [Max] General Discussion => Topic started by: j_forrester on 2015-01-14, 18:02:03
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When opening up Corona from scratch is there any true world camera value that EV 0 is equivalent too. I have looked up values on Wikipedia and it suggests a value of EV 9 for interior shots, when entering this number is becomes completely blown out. The reason I ask is because people I work with are trying to compare physical camera settings to Corona's EV values. I personally believe that is not equivalent to any value as EV is connected to aperture. When sliding the EV value whilst rendering the aperture (F-number) is not effected therefore is see this as more of an artistic approach. I know I can add a Corona Cam Modifier, but obviously locks off the EV value.
Can anyone shed any light on the out the box values or are they more artistic as presumed.
Thank you for any help.
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the EV control in Corona is relative to the base exposure, which is "output values are directly in watts per square meter per steradian"
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So in reality this has no comparison to a true physical camera starting point at EV 0 (i.e ISO, Aperture, Shutter speed for example) and more an artistic approach.
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yes, basic idea is that default exposure is artistic (you get 1:1 mapping), and photographic exposure is... well, photographic ;)
but I want to repeat - even the default exposure has physically well-defined meaning - white color means the surface emitted 1 watt per meter squared per steradian of energy into the camera
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The steradian (symbol: sr) is the SI unit of solid angle. It is used to describe two-dimensional angular spans in three-dimensional space, analogous to the way in which the radian describes angles in a plane.
(http://apps.usd.edu/coglab/schieber/trb2000/img021.GIF)
(http://www.troll.me/images/pondering-retard/pondering-retard.jpg)
Well, quite happy I am just the rendering guy.
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It means how much of light energy (in watts) is emitted from infinitely small surface patch, into infinitely small cone of directions. Other units like candela and lux work similar, they just have some historical names that hide the math to casual observer ;)
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When opening up Corona from scratch is there any true world camera value that EV 0 is equivalent too. I have looked up values on Wikipedia and it suggests a value of EV 9 for interior shots, when entering this number is becomes completely blown out. The reason I ask is because people I work with are trying to compare physical camera settings to Corona's EV values. I personally believe that is not equivalent to any value as EV is connected to aperture. When sliding the EV value whilst rendering the aperture (F-number) is not effected therefore is see this as more of an artistic approach. I know I can add a Corona Cam Modifier, but obviously locks off the EV value.
Can anyone shed any light on the out the box values or are they more artistic as presumed.
Thank you for any help.
It's actually quite simple. EV 0 means image units match 1:1. Or in other words, if you create light with intensity of 1, and measure surface of that light with color probe, you get exactly value of 1. Same with material with self-illumination assigned. Also, if you put in say environment map, exposure value of 0 means you will get exactly the same brightness as you see when you open the image in picture viewer.