mentalray color spinners greater than 1.0 and file format saving

[SgWRX]

1st - this might not be specific to mentalray, but recently i read about going higher than 1.0 for values within mentalray color spinners. for all my years i've NEVER thought to try typing in a number higher than 1.0, i just used the old spinner to get to 1.0. i'm trying to figure out why to do this, when to do this. seems like it'd be an artistic thing and or for getting eggagerated FG effects or self-illumination. perhaps "lighting up" part of a structure that might otherwise be deep in shadow compared to an exposure for the exterior?

 

2nd - it looks like 32-bit is really just 16bit + alpha. so to get the most possible colors out of a rendered image, it'd be OK to use 16bit tiff's or for that matter the .exr. that is, if i'm not concerned with an alpha. as far as post processing goes, in photography you can quickly run into posterization while adding mulitple level or curve or color edit layers if you start off with an 8bit rgb file, so typically you shoot raw (12bit depending on camera) and edit in a .tif or .psd file. it's the same with max renders eh?

 

thanks,

[Francisco Penaloza]

For your first question, could you point where you read that?

To me it does not make seance, I have no heard anything similar, if you have the link I would really interested in read about it.

 

For the second question, 32Bits mean double the bit data or light information than 16Bits, 32Bits is also refered as Full float.

Alpha channel have not relation between 32 or 16 or 8 bits, actually you can have that in any bit depth, it all depends of the format.

 

You are right when you compare the 32 or 16 Bits exr or hdri to the RAW files, thou RAW files are 14 Bits depending of the manufacturer, so exr or hdri at 16 Bits or 32Bits have way more dynamic range than a RAW file. this will give you more flexibility to exaggerate your lighting or do extreme transformations that 8 Bits image.

If you feel comfortable with 16 bits a Tiff file will work fine, or anything that support 16 Bits.

[SgWRX]

it looks like i found that info from a post on this forum from 2008: http://forums.cgarchitect.com/28142-ambient-occlusion-w-arch-design-material-exposure-control.html#post191725 it's a few paragraphs down... talking about the upper limit of mentalray not being 1, but the spinners limit you. all you have to do is type in.

 

i've played around with it and it could almost be like a self-illumination.

 

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ok - so just adding an alpha channel doesn't necessarily raise your bits in terms of # of colors per channel. in other words, a 16bit or 32bit image is always going to have more colors regardless of having an alpha channel. thanks!

[Francisco Penaloza]

First, that post is very old 2008, Mental Ray advanced a lot since them

Also I don't know exactly what was the problem that guys was having but to me, it was only wrong exposure.

Mental Ray works in real world scales, that's why the color spinner are from 0 to 1, other render engines still use RGB values, from 0 to 255 where 255 is the maximum. ( Mental ray amps goes to 11 )

Joke aside, Mental Ray uses linear full float values.

Are you just trying to gasp some Theory or you have an specific problem with your image?

I would recommend to read the Help that come with 3D Max regarding Mental Ray, there you can find up to date information of how this engine works.

 

Back in 2008 mental ray was just making it path in 3D Max, introducing new exposures system and all the new gamma stuff that confuse a lot of us for a while. but that is way gone, the system is more straight forward now.

[SgWRX]

just trying to grasp some theory... i've never read anything except that post that suggested you can set a value manually to > 1.0. I know that some situations the render engine will cause a > 1.0 pixel to be rendered, and right clicking on the rendered frame window will show various values for a pixel...

 

i've set an a&d material to be r 50.0 g 50.0 b 50.0 and rendered with FG and without, with/without exposure controls and find it interesting in results and when setting exposure in an external program like AE or PS if it's a 32bit hdr file.

 

i guess i wondered if there was some specific application they had in mind when they did that - i mean, if it's all physically based, why account for being able to set very high values?

 

no big deal, i'll probably find it useful at some point for non-physical renderings.

[satwinderdhariwal]

Files need to be 32 bit if you are going to be adjusting the exposure in post then they must always be saved in 32bit mode and later you set them to 16bit once youre happy with the exposure and gamma.

[Francisco Penaloza]

I worked for years using Mental Ray and I never had to fake that way the intensity of a color or material, why you want to do that? is beyond me.

Years ago some people try to render without exposure in mental Ray, I remember trying it too because by then (previews Max 9) the few exposure options we had where exponential so even though it worked great for overexposed whites or bright areas it clip the dynamic range of the image. Mental Ray for Maya did have better exposure controls(MIA exposure), and it worked in a linear way too, later on they unlocked that feature in Mental Ray Max and then they created the photographic exposure.

Having said all this, today you don't need to render without exposure, because photographic exposure will give you better results and faster rendering.

When you don't use exposure, the antialiasing of Mental Ray or any render engine work double, because the extreme contrast between bright and dark areas, it is just overkill.

If you setup your scene in a linear way, with Gamma 2.2 (by default now in 3D Max) and use photographic exposure, and keep all the light values consistent you can save as hdri at 32 bits or exr at 32 bit and you'll have the same light information range than non exposed images. it will be faster and you can always check what you are rendering instead to having a white image and hope for the best.