Cans

F.ip2 · Post by **F.ip2** » Thu Mar 15, 2007 9:35 am

terrific, slowly I seem to understand it a little bit.

I started to feel like pretty bad. I am not yet very familiar with the pre-pos-burn settings and how they affect the outcome.

What wonders me is this:

what is gain? I understand the watt - light energy. But when I change the gain nothing happens.

I have a hard time to understand how the three settings:
Gain - power(W) - efficacy(Im/w) affect the scene in conjunction with the Reinhard tone mapping.

In another thread I was informed that the power settings will be overwritten by the Reinhard tone mapping.

Funny is when I set gain, nothing changes, only with power(W).
I have my lamps at around 5 to 1 Watt which technically should not be ok.

I try most of the time to relate my real world studio work into here but obviously I am failing.

does the scale and distance of an object lets say the light in relationship to the background plane have a significant change? normally it should, the further away, the darker the background plane.

but i was not successful with that to simulate it in Indigo.

BTW: light diffuser: how would you setup a light diffuser - so that the light rays are scattered in all directions ?

suvakas · Post by **suvakas** » Thu Mar 15, 2007 9:44 am

Gain is ignored when efficacy is used. So you can forget about gain if you use efficacy

Suvakas

F.ip2 · Post by **F.ip2** » Thu Mar 15, 2007 9:47 am

rorrrrrrrrrrrr

so many options which influence each other.

this exporter should blend out options when you select one

step by step it all makes more and more sense.

manitwo · Post by **manitwo** » Thu Mar 15, 2007 10:19 am

But when I change the gain nothing happens.

if reinhard tonemapping is enabled, increasing the gain of your lights won't change the brightness of the final render. reinhard tm imitates the behavior of the human eye (which can "see" well exposed images independent from the brightness of the "lights", e.g. a dark room or a sunny day). If you take a picture with your (real)camera and it turns out too dark you wouldn't make the lights brighter - you would adjust your camera, right? For a brighter render you'll have to experiment with the pre/post and burn values of the tonemapping. As far as i know prescale controlls the brightness of the midtones(without burning) and postscale controlls the overall pixel brightness. "Burn" means the maping of the brighter pixels to pure white. Hmm, really hard for me to explain, look here:

The best way to learn what each of this values do is to play with violet and a .igi file.

It seems that much new users have problems in understanding how reinhard tonemapping works. (maybe someone, who is better in explaining things than me, should make a sticky in the tutorial-section

)

F.ip2 · Post by **F.ip2** » Thu Mar 15, 2007 10:28 am

you make a lot of sense - I understand what you say - like levels.
Not 100% the same but the theory behind is very similar.

I read the users manual many times but it is very techy. I guess somebody with the physical understanding will get it in a snap - not for me

Not that I don't know physics but the material here is a bit new.

I thank you so much for all the help.

dougal2 · Post by **dougal2** » Thu Mar 15, 2007 10:29 am

i see reinhard tonemapping much like audio compression (being that I am primarily an audio engineer). I've no idea if that's a useful analogy to anyone...

prescale = gain before dynamic range compression
burn = compression ratio
postscale = post compression gain

F.ip2 · Post by **F.ip2** » Thu Mar 15, 2007 3:46 pm

so reinhard than produces different results depending on from where you see it? if you look into a room or out of the room is different for your eyes.

i ask that because i get different color / exposure results with the same scene
just having different camera positions.

guess i should try out the linear mapping

mrCarnivore · Post by **mrCarnivore** » Thu Mar 15, 2007 9:31 pm

F.ip2 wrote:so reinhard than produces different results depending on from where you see it? if you look into a room or out of the room is different for your eyes.

Yes, you're right. It only depends on the visible frame. tonemapping is computed on the rendered frame and independent from the rest of your scene. So if you change the camera angle and in the final render there are more objects visible that are bright resulting in a _brighter_ render before tm, then the overall image will be _darker_ after tm (if you use the same tm parameters, of course). This is the same effect as with our eyes.

As somebody mentioned before: Tm is basicly an autoexposure tool. You can get the same results with your digital camera...

F.ip2 · Post by **F.ip2** » Fri Mar 16, 2007 5:03 am

perfect now i finally understood it !!!