xeunox

Ok let me begin by saying that I've been battling with bitmaps and the daylight system using mental ray sun and sky and mostly using Arch and design shaders (for this post I'm only using arch and design shaders)

FG set to draft for this post (bounces 7)

Required texture in daylight lighting



Problem 1:

Keeping bitmaps on a standard RGB level of 1 causes the rendered image to be overexposed or "washed out". (Fig 1)



Problem 2:

Setting bitmaps RGB level down to 0.3-0.7 causes the vibrant colors to fade drastically, causing the entire image to look "faded" (fig 2a,b,c)



Fig 2 a, Fig 2 b, Fig 2 c


Problem 3:

Using Logarithmic exposure control by changing the brightness and contrast only yields the same effects as problem 2, causing textures to loose their vibrancy or to become over dark.

Solution: (big up Jeff Patton!)

Setting gamma settings helps, I got this tip from http://jeffpatton.cgsociety.org/blog/ which solved my problems after alot of tweaking, (fig 3a,b,c) really brings out both color and correct lighting. Even with this I'm still not entirely happy with the render, its seems dull and flat. Maybe I've just been staring at my screen for too long i don't know.



Fig 3 a; Fig 3 b, Fig 3 C

This is great and all but why make it so "non" standard. Figuring out to use blown out gamma setting, fig3c.jpg where the gamma is set to 4, which in my opinion is simply put, ridiculous.

Maybe I'm missing something but I hope this helps the next person having similar problems. Another setting you might check is the global gamma, make sure it is set to 1 and you will have to save your work and restart max with each gamma setting change.

Justin Hunt

Have you tried the mia-exspoure simple shader? dropped into the camera leanse slot in the render dialgue and controled through the material editor it gives alot of control over the brightness, contrast, mid tones as well as the gamma settings. It also doesnt wash out bitmaps.

check out this thread on the my mentalray forum http://mymentalray.com/forum/showthread.php?t=611


The other is to drop the diffuse level of the material. Basicaly the arch and design shader will automaticaly ballance the difuse level, reflection and transparency down to 1. However this may not be enough as even at 1 the material can be too bright. Dropping the diffuse level causes more light to be absorbed, thus the surface appears darker and specular reflections are clearer.

JHV
JHV

xeunox

i will check most definitely read up on that in the near future, unfortunately my dead line is tomorrow and i have very little time left

thanx man, will definitely check out after the dead line and a couple hours sleep. RED EYES FTL!

Justin Hunt

veels geluk

JHV

muchhal.sandeep@gmail.com

Thanks guys

Thanks a lot
I was suffering from this disease since long.

now thing that got the required treatment for cure.......

thanks a lot::::::::

Big problem is now solved:

Regards:
Ar. sandeep muchhal

Brian Bradley

Hi xeunox,

I'm a bit puzzled as to why you would be changing the
values in your Gamma preferences whilst keeping the
Log exp values at their defaults? Those controls are
what you need to play around with, just as you would
play with your camera settings out in bright daylight.

The Log exp is very useable under most conditions, and
can produce great results.

Regards
Bri

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Macer

New version out soon (Max 2008) has a new type of exposure control for MR incorporating some new features (including vignetting) and is supposed to prevent the image from becoming as washed out as it can with log exp.

Looking forward to getting my hands on it soon!

xeunox

Brian i have found that using exposure controls usualy ends up making the whole image milky or too dark. but i'm not the expert, i actually figured out the mentioned problem above as i was writing the post, and decided to share it anyway.

The MR_exposure_simple lens effect that Justin posted works a dream as well, but still for a relatively newbie too mental ray i don't think my method is too bad for a quick fix to a general problem, specifically when it comes to actual use of bitmaps.

Brian Bradley

Hi Pieter,

It was the fact that the set up would give washed
out results that puzzled me as to why you hadn't
done some work with the contrast and mid tones
settings. Tis a little difficult to get it all crammed in
the head I know. :-)

Here is a post with a render from our upcoming
module that uses Log Exp in the final Render.
Hopefully shows it can be used for decent renders!

http://www.cgarchitect.com/vb/26284-exterior.html

Regards
Bri

__________________
3Ds Max - Mental Ray - VRay - Brazil Training Modules
www.mentalboutmax.co.uk
The MBM Blog
www.mentalboutmax.blogspot.com
Vray Learning Resource
www.vrayelite.com

Justin Hunt

Just a plug for Brian, I would highly recomend getting Brians module that covers Exposure control. It taught me a few things and gives a good expination, although (sorry Brian) he doesnt explain the mia_exposue simple shader properly. Follow Hot Chips tutorial for that.

With Jeff's, trick it is only acting as a global way of setting incoming texture maps to a specific gamma. It is in no way meant to act as a means of correctly exposing the image correctly.

JHV