difference between exponetial and HSV esponetial

[cocolas]

I was wondering if anyone can explain the diference between the two, and if there is one that's more approriate to use.
I see that HSV expo. tends to over saturate materials while exponential tends to desaturate them....so I'm having a hard time finding a balance....

thanks

Paul

[cocolas]

OK I'm getting really frustrated with this exposure stuff:

1st:

why do I even have to use an exposure - I mean in FR and brazil it seems like you don't have to use exposure if you don't want to - here one has to be selected.

2nd:
the 2 setting for each (darker/brighter) seem very simplistic and inadeguate and they trow off all the colors/mats in the scene (either oversaturated or washed out).

3rd:
anybody care to explain what exposure you use and most importantly WHY.

this exposure seems more pain than its worth....

paul.

[yog]

The reason we have exposure settings is that most renderers work in a physically correct way like a camera.
Walk into any room with small windows and it all looks OK. Now take a photograph of the room and depending on your settings some parts of the picture will be very under exposed, whilst others will be very over exposed. This is why 3D renderings of internal scenes with external lights is so tricky without adding several other lights. This is also more or less the way the Linear Exposure setting works in Vray.

What the other exposure settings in Vray are trying to do is get the render to be more representative of what the human eye sees, i.e. multi-region light balanced.
What most renders do is once a surface colour is lit past the 255,255,255 range, it "clamps" the colour to white, in 8 bit renders you can't get brighter than white.
What the Expenential Exposure does is take all the colour ranges including the highest and lowest un-clamped colours and performs a scaling factor to the brightness value in order to try and fit the whole colour range into the 255,255,255 8-bit format. The downside is some of the colours become more muted.
the HSV Expenential Exposure setting is more pleasing to the eye. It too is trying to adjust all the colour range (including the un-clamped colours), into the 8-bit range, but instead of adjusting just the brightness it is adjusting the Hue, Saturation and Value of each colour range in order to give a more "natural" balance colour range.

The upshot is that if you want a very contrasty "photograph" look, leave the setting at Linear. If on the other hand you want to light in the scene to be well balanced like the human eye sees it without adding a number of additional lights, then set it to HSV Expenential.

[flipside]

If you select linear, this means no exposure, just normal rendering as in any other package.

Try to render an interior scene in fr, lit only by a sun+skylight or only by skylight. Impossible to get enough light into the scene without adding other lights. or when you do get enough light into it, your multipliers need to be so high, that all areas lit in the first bounce wil get very very blown out. What I did in fr is give all blown out parts another material with local GI multipliers to prevent it from being blown out, this is not an easy method...

In vray just select exponential color mapping, turn up your light and skylight multiplier and you will not have blown out regions. Indeed colors of materials change, but you can never create materials by judging the material preview because it is lit in a completely different way. (using colored lights also changes you material colors, and nobody seems to have a problem with that).

A similar effect to get a brighter image in fr is to set the contrast spinner to -50 or even -70. This will brighten up your image a lot, but again, colors change too.

It's like yog says, it's all about how we humans percieve light. If there would be a camera that does the same thing as our eyes in conjunction with our brain, we wouldn't need to tweak much the lighting multipliers etc.

Try to take a pic with your camera where you have a floor lit by strong sunlight and areas more inwards in the room where only light reaches after 5 bounces, you will have the same problems as in a rendering, blown out regions.

[cocolas]

that makes sense....

yog:

HSV Expenential Exposure setting is more pleasing to the eye. It too is trying to adjust all the colour range (including the un-clamped colours), into the 8-bit range, but instead of adjusting just the brightness it is adjusting the Hue, Saturation and Value of each colour range in order to give a more "natural" balance colour range.

as you say, since HSV affects these different aspects, i wish there was more control in vray to tell it how much to affect each of these aspects (HSV) ....
the "darker" and "lighter" options seem a bit too semplistic/inadeguate to handle and allow for fine control over these exposures

thanks guys.

paul.