Good Day SESI community,

Are you an artists or TD with photographic/cinematographic training who has been confused by the addition of the “exposure” control into the light interface?

After trying to wrap my head around what the he## an “exposure” control (which is specifically and exclusively a series of camera settings) is doing on a light, I contacted SESI support. The response was that, the control name is

“based on the effect the control has, disregarding the fact that it doesn't exist in the physical world.”

What the???

They say:

“While real world lights obviously don't have a concept of exposure, the effect of changing exposure on all CG lights in your scene is the same as changing it globally on your camera or render, so there's a natural correspondence. It appears to be intuitive to most artists and is an often requested feature, so I'm afraid it's here to stay.”

Aside from the fact that this is fundamentally false, did anyone here ask for a second light intensity control called “exposure” to be added to a light? It's like having two sets of transform coordinates, but one is exponential.

What this control does is exponentially control light intensity. So now we have two light intensity controls, one that moves light intensity linearly and one that moves it exponentially. This isn't terrible(except for its name), but I'm curious why a lighter can't simply type in higher values like 10,000 or 10,000,000, which are totally natural light intensity values.

I suspect it may have something to do with the widely held belief that lighting artists should never turn their light intensity values above 1.0, which is actually quite ludicrous when you consider the actual light intensity values that exist in nature. It feels like this extra control was added to crank up light intensity in a way that lets artists pretend they're still keeping light intensity values below 1.0. If true, this is actually harmful to the development of lighting artists understanding of the true nature of light. Lights should often be cranked way up. They're really, really bright.

Now, I don't have an objection to a second exponential light intensity slider per se…but two things really should happen here. First of all, it should NOT be named “exposure” (more on that in a moment) and second, the actual intensity value that results should be displayed. Right now, if you turn a light up to 2 and then crank the “exposure”, you think your light intensity value is still 2, but it is not. The real value is hidden from you. Not so easy to do real light ratio calculations when the true light intensity value is hidden.

Why It Should Not Be Called Exposure

Exposure is a well-known global value in photography which is very exact. It refers to how much light reaches the exposure medium. Exposure can not be controlled on a per-light basis. Exposure can be controlled at the camera using a number of methods including:

1. Aperture-Fstop or Tstop
The aperture is a variable hole in the lens housing that limits the amount of light from all light sources getting through. Change in aperture varies depth of field. The light “exposure” control does not do either of these things.

2. shutter speed/angle 1/xx or degrees
Shutter speed (still) or angle (moving) varies the amount of time the exposure medium is exposed to all light sources. Change in shutterspeed/angle varies motion blur. The light “exposure” control does not do either of these things.

3. filmstock/ISO various known values
Filmstock/ISO varies the sensitivity of the exposure medium to all light sources. Varying the filmstock/ISO changes the grain quality of the captured image. The light “exposure” control does not do either of these things.

4. ND filters
Neutral Density Filters placed in front of the lens change the quantity of light entering the lens from all light sources. This is the most like the light “exposure” control, except that it acts on all light sources, not just one.

So If It's Not Exposure, What Is It?

Well it's in a scale of -10 to 10, which doesn't correspond with any established exposure control. Going out of default range very far can really wig it out too.
It is simply exponential light intensity control and should be named appropriately. Furthermore the total light intensity from this control should be displayed.

Who Cares?

Anyone with photography or cinematography training, and everyone once SESI develops a physical camera and has to implement real exposure calculations, at which time they will be obliged to rename this control anyway, causing further confusion later.

It makes no sense to co-opt the name of such a well known set of camera controls (exposure) to change something which is clearly and absolutely not exposure. This causes nothing but confusion, especially among photographers.

I teach lighting. At my school, where we also teach photography/cinematography, we have to teach that there is a light control in Houdini called “exposure” which is nothing like the exposure controls we teach in photography class. We have to teach that it really just changes individual light intensity more radically than the regular light intensity control and that it does not affect exposure in any way. This is the only way students with photography training can make any sense of the control.

I believe it is essential to keep parameters sensibly named. And although SESI states they think “exposure” is intuitive, for photographers, it is exactly the opposite. It is further my opinion that any CG photographer ( we call them lighting artists) should be well trained in camera. The cg camera is, after all, supposed to be a virtual analogue of the real camera. We are virtual photographers.

I look forward to opinions on this and, hopefully, decent alternative names to this control.

Next topic: Lets get a physical camera under development!! All in favor?

If you made it this far into my rant, thank you for taking the time, I apologize for taking up so much of your day.

Nick

Hi Nick,

I have seen this control that you are speaking of although since I'm new to Houdini and have been working on my first project for the past year I haven't got to the finer details of lighting/rendering other than getting some simple render set just to know what I have will “work”.

I do have a background in using film…use to be an outdoor photographer and took thousands of pictures.

If the exposure control is like an exponential factor vs. the lighting being a linear one then to me this control you speak of does make sense to me, even though it does not have a direct correspondance to using film in real life, it does conceptually.

To me the lighting ( its linear aspect ) relates to the aperture/shutter speed relationship while the iso relates to the exposure.

Even with the same iso film an aperature change of one f-stop at the lower end of the lens' limit will not yeild the same comparable result( same change of aperature eg. alter one f-stop) of aperature/shutter speed at the other end of the lens' limit. So in a certain way its not really linear, but what is constant is the particular iso film being used and an aperature/shutter cominbation for that particular film.

But those differences as I just mentioned going from one end of a lens' capacity to another is even more exagerated when you compare two different types of films. Like for the same scene I would sometimes switch out from an iso 800 print film to a 25 slide film. And the required aperature/shutter combinations are very much different between the two films to get intended results.

I liken this as the exposure control ( again as you say - assuming its exponential ) - one exposure level (iso) compared to another exposure level will not give you the same range/results with your lighting control(aperature/shutter).

Perhaps this is just all ‘graphic’ semantics…shall we call exposure iso?…I don't think so..after all not all animation scenes have the intention of depicting something in real life…my own project that I am working on has nothing to do with what one would see in real life…so maybe changing the name to reflect a ‘physical’ camera might not be a good idea.

Hi Babaj,

To be clear, when we say “exposure” in photography, it is short for “exposure to light” or even longer “how long the film/CCD is exposed to light” or “how much light reaches the exposure medium through variable aperture and shutterspeed/angle.” One can't really say that aperture and shutterspeed does not control exposure, as they are the primary exposure controls. Exposure is a global control that affects all light reaching the exposure medium. It still doesn't make sense to rename individual light intensity to exposure.

For further clarity, the light “exposure” control only controls the light intensity of a single light, not of all lights in the scene, which might make more sense.

I guess film ISO doesn't really belong there as it's sensitivity rather than exposure control and generally used when we reach the limits of our exposure controls.

Certainly not all renders are photoreal, but that doesn't mean we can take the word “colour” which is well known and use it to describe displacement or take the word “rotation” to mean “translation”. And no, this is not an exaggeration.

Taking the word “exposure” which is a set of universally well-known camera controls and using it to describe individual light intensity is…kinda weird.

Nick

Here's an excerpt from the Arnold Documentation:
https://support.solidangle.com/display/AFMUG/Lights#Lights-Exposure [support.solidangle.com]

The reasoning behind this apparent redundancy is that, for some people, f-stops are a much more intuitive way of describing light brightness than raw intensity values, especially when you're directly matching values to a plate. You may be asked by the director of photography (who is used to working with camera f-stop values) to increase or decrease a certain light by ‘one stop’. Other than that, this light parameter has nothing to do with a real camera's f-stop control. Also, working with exposure means you won't have to type in huge values like 10,000 in the intensity input if your lights have quadratic falloff (which they should).
If you are not used to working with exposure in the lights, you can simply leave the exposure parameter at its default value of 0 (since 2^0 = 1, the formula then simplifies to: color * intensity * 1).

Hope this helps.
Andy

Hi Nick..

One can't really say that aperture and shutterspeed does not control exposure

..and I wasn't implying that…but what I was saying is that aperature/shutter speed are more linear hence they relate better ( to me ) with light control.

And yes, iso relates to sensitivity but that sensitivity is much greater from film to film depending on the iso and type of film ( film vs. slide ) such that it represents more of an exponential factor.

One cannot ignore the type of film one is using ( iso ) ie. the same aperature/shutter combination will simply not work for another iso rated film. Hence ‘exposure’ is more than just an aperature/shutter consideration.

So in the end you have 2 considerations:

Iso and aperature/shutter speed

or in the controls:

exposure and lighting.

Because in just about every show I've ever worked on, lighting dailies with the art director/lighting supervisor will always, ALWAYS talk in terms of relative stops.

Now that most tools for manipulating images (RV, nuke, baselight etc) work in linear floating point, this means at any stage of the pipe anyone can say ‘bring this down by half a stop’, and everyone knows exactly what that means.

The days before talking in terms of EV, and everyone tried to guess what people meant by ‘half the brightness’ or to try and estimate actual intensity values, were dark days (pun intended).

Yes we could go down the path of matching iso and all that, and I know of a few one off commercials that have done so with render engines that support it (like Maxwell), but generally that's a bridge too far. There base assumption is there lighter generates a well exposed image, and notes are taken relative to that.

Hello ladies & gents,

I don't disagree that exposure , Fstop, Tstop, shutterspeed/angle should be a part of our toolset. Absolutely they should. But they should do what they do in a camera not something vaguely similar that can be roughly explained through convoluted logic. This control is not analogous to F-stop or Tstop, which affect all lights. This is a per light intensity control.

We have two things on set related to light. Lights and a camera. Lights put out a certain quality/quantity of light. Cameras receive it. Light intensity controls the quality/quantity of light coming OUT of particular light source. (This is what the new houdini light “exposure” control does). Camera exposure affects the light coming IN to the camera. the new houdini light “exposure” control does not do this. It's pretty simple. The exposure control doesn't control exposure.

We need a physical camera with functional exposure control.
For an example of a great physical camera, have a look at VRay.

In Houdini, the shutter“time” and fstop controls have no effect on exposure. There is, effectively no exposure control in houdini, making light intensity values arbitrary. So I can see why people are asking for exposure control, but it would be nice if that was actual exposure control, not a secondary exponential light intensity control, per light.

@Andy58, thanks for that quote. It is my opinion that lighting people SHOULD have to use huge values like 10,000. In this way they can begin wrapping their heads around the real nature of light. That's what real light intensity actually is! It is essential we break away from the old thinking that lights need to be at or below 1.0 int. Artists who start to get a handle on how friggin bright lights actually are tend to do better work and use their tools better, IMO.

Nick

*shrug*

Tell every lighting department in every studio to use absolute intensity rather than exposure. Once they've all agreed, then you can demand sidefx change their knob.

Would love to see a physical camera system that mimics Vray in Houdini, but every renderer I've used has funny quirks and methods so I've always just chalked up this exposure setting in the lights to that. Certainly had me confused at first though

lor
@Andy58, thanks for that quote. It is my opinion that lighting people SHOULD have to use huge values like 10,000. In this way they can begin wrapping their heads around the real nature of light. That's what real light intensity actually is! It is essential we break away from the old thinking that lights need to be at or below 1.0 int. Artists who start to get a handle on how friggin bright lights actually are tend to do better work and use their tools better, IMO.

In my experience, lighters care more about creating a pleasing image and matching lights than actual light intensities. And the option of stopping up and down lights with ‘exposure’ is predictable and much appreciated. People saying light inensities shouldn't go above 1.0 is something from the days preceding linear workflow. It's not something I've heard or seen done in years.

Just curious, since you seem so focused on real world parameters – what unit for light intensity do you propose?

Andy

mestela
*shrug*

Tell every lighting department in every studio to use absolute intensity rather than exposure. Once they've all agreed, then you can demand sidefx change their knob.

That's not the point. The point is that this knob doesn't do exposure, yet is called exposure.

N

Andy58
In my experience, lighters care more about creating a pleasing image and matching lights than actual light intensities. And the option of stopping up and down lights with ‘exposure’ is predictable and much appreciated. People saying light inensities shouldn't go above 1.0 is something from the days preceding linear workflow. It's not something I've heard or seen done in years.

Just curious, since you seem so focused on real world parameters – what unit for light intensity do you propose?

Andy

Andy, I agree, exposure stops are a great idea and also that the pleasing image is the more important goal. Problem is, this parameter doesn't do exposure. As for lights not above 1, major studios in town have CG supervisors directing junior lighters to do this. So it's still rampant, unfortunately.

The major block here seems to be that people think I'm against an exposure control, which I'm not. I'd love one. There isn't one in Houdini yet. what they've done is added a second light intensity control and improperly named it exposure. We can fiddle with it as much as you want, it will never change the exposure of the image.

Nick

I think having it called exposure on the light makes sense. Lights have the same parameter in Renderman, and Arnold by the way. I'd rather SESI not deviate from what's more or less becoming an industry standard at this point. The idea behind it is that if you were to look at a single-light render in the image viewer then increase/decrease the exposure to find some values you liked better, you could then go back easily adjust your light exposure values to match the exposure value you liked in the image viewer – and it would match.

The problem I can see is that in Houdini there are no real exposure controls elsewhere – mplay/render view need a real exposure option to actively work like that, cops should have an exposure node, and as mentioned earlier a good physical camera like the one in vray. I'll log RFE's for that. I suggest you do the same.

The brightness control in MPlay/Render View/COPs do have +/- buttons beside it, which double or halve the brightness.

^Yes, but is it the same as exposure? The +1 on brightness certainly isn't in correlation to the +1 exposure on a light. In katana we have an f-stop hotkey that matches the light intensity, as well as in our image viewer, and also I believe the f-stop setting in nuke is the same. I could be wrong there.

Bightness is 2^Exposure, and that's what the field is showing. The buttons double or halve the brightness, which is equivalent to +1 or -1 exposure.

twod
Bightness is 2^Exposure, and that's what the field is showing. The buttons double or halve the brightness, which is equivalent to +1 or -1 exposure.

You just blew my mind. Or I'm going crazy. I swear I tested it and it wasn't working the way I expected it to at all. Sorry about that

I figured it out - I was typing in the matching values, not using the buttons, which I see do the right thing.

Discussing an image exposure in f-stops is just natural for a lighter and every supervisor/DOP communicates that way. While we understand the relative meaning of both intensity and exposure perfectly having exposure under controls is not an annoyance ever, it's just convenience. Exposure is your friend

sigh

A lot of work these days does not use traditionally trained camera/lighting people. They will happily look at a monitor or grade and just make it work. Any digital artists unable to deal with an extra control called ‘exposure’ is not quite right for the industry these days.

Sounds light Ior is simply advocating his business model of traditional training… lol. Next he'l be deriding the Richter scale for not showing earthquakes in a linear form so people truely understand the power of nature.