I got quite a few requests for my umbrella light props, they are now in the free stuff area.
Missy woot!

www.renderosity.com/mod/freestuff/details.php

Quote - Oh, and one more thing, for the record...

Quote - Also, my main light is neither a normal light, nor a specular only light. It is in-between. Look at its shader. The Diffuse_Color is RGB 96, not 255, nor 0. Clever? Eh? Eh?

Yes I invented it. What shall we call this sort of light?

Sorry for not participating - I've been overly busy with work. Still am, but I need to have fun, too, so here I am.

I'm sure that's a tongue-in-cheek claim. I've been using this type of main light since my early IDL testing days, implemented my own way... see screenshot. :O)

Sort of tongue-in-cheek, yes. If we accept that invent implies "discovered or devised for the first time, ever", then I have no idea who invented it. On the other hand, if invent implies "publicly revealed a working solution for the first time", then I think I did invent it.

It's quite possible that a technique can be discovered by multiple people independently, and so it's fair to say you invented it, too. It would have been more accurate for me to say that I'd not seen anybody write about this technique and I came up with it for use in this context on my own, as opposed to being told about it.

Regardless, the important thing is we're using it and we know why!

Quote - One more thing for possible discussion. I notice that the main and rim lights in the tutorial scene have fall-off set to inverse linear, rather than inverse square. I have not yet found any mention of this in the thread. Was this simply the default, or intended that way?

And how is the light fall-off from the light box treated? I'm going away to find out....

It probably doesn't make much difference in an empty environment with a single centre-positioned subject, but with surrounding or backdrop geometry it surely would.

Correction: I suppose it would also affect the bounced light from the left hand wall.

I intended it. To fully understand light falloff would require that we discuss some serious calculus involving double integration. Do we want to or no?

The inverse square rule is 100% accurate only for point light sources - having no measurable dimension in any of the 3 spatial dimensions.

The inverse linear rule is 100% accurate only for infinite straight line light sources - an infinite tube with a diameter of 0, thus having only 1 dimension.

To truly describe the luminous intensity field created by a glowing object, we have to fully take into account the position and orientation of that object, its actual shape and size, and the actual position and orientation of the surface receiving the illumination. The correct luminance is never inverse linear nor inverse square, nor any given constant power.

Short of going back to something like my ISF light shader, however, we have only two choices - inverse linear or inverse square.

Which is more correct?

Inverse linear says luminance is proportional to (1/d)^1, and inverse square says it is proportional to (1/d)^2. Generalizing, we can say that light falls off roughly as (1/d)^p, where p is some power. For most shapes and distances, the power, p, is actually between 1 and 2.

In general, (and this is a gross oversimplification), if we're talking about some sort of finite object as a light source, the value of p is above 1.8 when the distance to the light source is at least 5 times the diameter of that light source. And regardless of shape, p is 1.95 or higher when the distance is 20 times the diameter of the light source.

But what happens when we're closer than that? What if the light source is a 6-foot umbrella and the subject is about 6 feet away? What is the falloff then?

The answer is very complicated. To the best of my knowledge, caclulating the exact answer is very difficult and/or impossible in terms of a closed-form mathematical equation, even for a flat, square sheet of light. (At least, Wolfram Alpha says there is no closed-form answer with traditional math functions.) For something that isn't flat, like an umbrella, it is even more complicated, because there is a focusing effect.

Focusing is very important, because it prevents the uniform spreading of light on an expanding sphere. In the neighborhood of the light source, it is possible to see little falloff at all within a rather large area of bounded space. In the case of an infinite sheet light source, there is no falloff anywhere - the illuminance is a constant throughout the entire universe.

So we must resort to numerical methods (approximations) for bounded 3D objects like umbrellas. I did a calculation using a parabolic square, where the depth in the center is 1/2 the diameter.

Then, for any point along the central axis defined by this virtual umbrella, I calculated the rate of light falloff as a function of distance from umbrella, from the reference point of the center of the square assuming it had no depth. (Imagine an umbrella with a shaft passing through glass, with the perimeter touching the glass. The point where the shaft passes through the glass is my reference point for distance.)

Here are the falloff results showing distance (as a multiple of diameter) and the falloff power.

.01 => .03
.05 => .13
.1 => .24
.2 => .46
.3 => .64
.4 => .79
.5 => .91
.6 => 1.01
.7 => 1.02
.8 => 1.18
.9 => 1.24
1.0 => 1.3
1.2 => 1.4
1.5 => 1.49
1.75 => 1.56
2 => 1.61
3 => 1.73
5 => 1.84
10 => 1.92
20 => 1.96

Notice the early values, where the distance is a small fraction of the light source diameter. The falloff approaches 0. That is because at such a distance, the umbrella is much closer to behaving like an infinite sheet than anything else. An infinite sheet has no falloff - the value of p = 0 in that case.

So what does this mean? Suppose you have a 6-foot umbrella and you measure falloff at a distance of 9 feet. That is 1.5 times the diameter, so look above for 1.5 and we see the falloff power is 1.49. This is halfway between inverse linear and inverse square. At this distance, neither setting is more correct.

However, remember that I'm mixing a glowing rectangle with the spot light. The glowing rectangle is going to push the results away from what we get from the spot light alone. And I found that given the choice beween p=1 and p=2, p=1 produced better results in that mixture.

So, in general, for a distance somewhere between .4 diameters and 2 diameters, inverse linear is a better approximation on the spotlight that is trying to behave like an area light. For a 6-foot umbrella, that would be 2.4 to 12 feet. This is the range I was shooting for in soft studio lighting.

We could make a light shader that implements this equation. However, it would require quite a few nodes. Poser doesn't have an arctan function, so that one term would have to be expanded as a Taylor series. And - it would still only be correct for points in space that lie along the central axis of the light source. Other points would be wrong. It also assumes the lit surface is pointing right at the light source. If the normal is pointing elsewhere (as it does 99.99% of the time) the equation becomes even more ridiculous.

BB, I love when you do that.

I finally stumbled onto this thread and am still catching up.

I have Poser 8 and Poser Pro 2010 beta, so could try some simple comparisons. I've lately been using 2010 exclusively; its 64-bit in-the-background renderer finally let me produce I picture I've wanted for a long time.
 
I need to mull things over a little more before posting anything as I don't want to divert this thread.

Whichway
 P.S. - Anybody have a back pointer to the Artistic Lens stuff? It seems familiar but I think it popped up out of the blue on this thread. Thanks.

grinning And to think that once in my youth I was considering going into physics as a profession.

Poor me - I did.

Poor you! Now I'm just interested in making a good looking image in Poser. So I pour over discussions like this taking in what I do understand and grabbing screen shots and/or demo scenes.

Assuming a square sheet centered on the origin, and a point being lit aligned on the z axis, the contribution of any infinitesimal point on that sheet is

1/(x^2+y^2+z^2) where x,y identifies a point on the sheet and z is the distance from the origin of the point being lit.

The attached image shows what needs to be computed. Can you do it?

We actually need the definite integral where x and y go from -.5 to .5.

Not anymore, I can't, at least not without a struggle. But I think you're pressing way too hard for precision here where it is not justified. Poser couldn't do it anyway.

 BB, I'm looking forward to your outdoor scene. For some reason blue skies negate the color of skin on my characters (I'm using VSS) so it's almost a bluish grey. Is there a way to stop that and still keep the sky to a daylight blue?

Yes - white balance your camera. LOL Just kidding. There's no such control in Poser, although there should be. We should have camera white balance and exposure settings that do what real cameras do.

The trick is to make your sunlight yellow. Exactly what yellow is - well - the point of the tutorial scene.

 Well, that makes sense, actually, on both things, and now I understand why I was having trouble. Thanks! Now to await the tutorial scene and data mine it with glee.

Quote - Yes - white balance your camera. LOL Just kidding. There's no such control in Poser, although there should be. We should have camera white balance and exposure settings that do what real cameras do.

The trick is to make your sunlight yellow. Exactly what yellow is - well - the point of the tutorial scene.

what i do for my outdoor renders is :

i first use your ENV sphere that is blue. i make the sun yellow. i also add a white box. this is a small render with bad settings. then i import this in photoshop and white balance based on the white box.then i use those settings in photoshop for my final render and it looks like in real life.

i watched a DVD for cinematography. and they explained how they do white balance on set. they put infront of the camera a white paper and WB the paper.

Regarding simulated umbrella lights - I don't think it is really necessary to simulate the 3d shape of the umbrella and bounce light around in it. You could use a simple glowbox but feed an intensity mask into the Ambient Color slot of the glowbox's surface node. For example, something that blackens the corners of the box would give you a proper imitation of the shape of the light and, if you really wanted to, a radial gradient centered on the mask would give you the effects of any non-uniform illumination of the umbrella. This would, of course, only work for the diffuse component of the illumination of the subject and then only with IDL turned on, but umbrellas are for making soft, i.e. diffuse, lighting anyway and the IDL algorithm will then calculate the falloff in a statistically correct manner. Mostly, I don't think you'll see significant differences.

Whichway

the glow doesnt look good IMO.

It does seem a little odd that it is lighting up the back of the hand.

Whichway

the lite-emitting ball in hand is not illuminating the back of the hand.
as poser lite-emitting surfaces don't interact with atmosphere yet, latex either added
second ball in poser to simulate atmosphere/aura, or added same in APS.
note to latex: ball can be as bright as you want it, however these computer screens are
limited in their display of luminance.

When I have time, I will publish a tutorial.

 Sweeet, now you can create fireballs for wizards and witches right within Poser!

The halo effect is an extra ball add over the original glow ball. I believe the halo glow effect was shown by Oliver over at RDNA a long time ago. BB, would love to know how you did your glow ball. In my image there is only one spotlight and the glowball.

Whichway

I would suggest getting the VSSPR3, there are more refinements to the node structures.  Yes, if you use either poserPro or PoserPro 2010, the gamma correction value should typically be set to 1.  The skin looks a bit reddish, you may need to adjust sub skin scatter.  Otherwise, the render looks very good with these settings.

I will look into the details of VSS3 next.

Whichway

Definitely, better.  When you do try VSSPR3, there are GC nodes for the eyes which need changing if you continue to use the Pro versions.

Whichway

Actually, I lost track of the VSS version numbers. I was working from VSS pr3. That was the template material set I started from. I think I like my eye shader better; at least I can justify it to myself better. Basically, I modeled the surface of the eye as covered by a film of water, so I used a form of Fresnel reflection off the EyeSurface with some Glossy folded in. I used a transparency mask so that the transmitted part of the light over the sclera passes straight through to the sclera's color map underneath. Over the cornea, the light refracts through a transparent cornea down to the iris. Tear is basically a fresnel node with glossy added so the direct lights show up. Lacrimal is the same as skin, but with glossy added. For the sclera, I used the straight colormap. It looked to me as though the VSS pr3 Template Eyewhite was practically the same as the Template Skin in VSS pr2. Since the sclera is such a different tissue from skin, things like SSS, bumps, etc. probably don't apply. Anyway, that was my thinking.

Whichway

bagginsbill when will you post the tutorial for white balance ? :) 

please today

Quote - > Quote - I got a wild idea and decided to try it. Took a few hours of tweaking and rendering before I was happy with it. What I did was bring in Bb's EnvSphere and applied the ambient shader from his light box. I deleted all but one spotlight that was pointing at my figure's head and played with the balance of the light and the ambient on the EnvSphere until I got this.

Also very good! I love how the speculars played out on the skin here.

You jumped ahead of the class! I was going to do a scene with the "glow sphere" technique, too! Do you want to give me yours? I'll post it on my website if you like with the other(s) - yes there will be more. I've started working on the "bright sun outdoor" set.

Here's a preview. This is a work in progress - not finished yet. I mixed up the materials on the car by accident, leaving the wrong one on the bumper. I'll fix that and post the materials for the car, too. Also, the ground with puddles will be included.

Will you tell us about the glow sphere technique?

I haven't sorted out the Cloud layer fully yet. I suspect it is a 2nd Sphere that is x% larger and the Noise applied to it.

Here is a render with two Glow Speheres and BB's IDL Wall material as the ground.
No lights in the scene.

 Indeed it is two spheres, as he mentions in the first post of the glow sphere image, and the second sphere does have the turbulence effect.

Using these glow objects, you could create a great nightclub lighting scenario with the wide variety of light colors in clubs.

I was actually referring to an EnvSphere as a light source for a scene, but looking at the mat room settings you posted I think I have a pretty good idea of how to do it.

The EnvSphere is already 'wired' for self illumination and can provide a source of light.

Quote - I wanted to share what I´m working on using the SoftStudio.  I put the main light straight above the character and the rim light behind the character.  I put a disc primitive on the floor and plugged a radial gradient map to the transparency, ambient and reflection nodes.  I still have some work to do on the pose before I render it out and ruin it with postwork in Photoshop ;)

Sweet.
How would it work with some Atmosphere??

Thank you Mariner.  I´m thinking about adding some smoke whispers and fog in Photoshop before posting it to my gallery.

That's really great, Vestmann. The lighting is very convincing.

Thanks Bagginsbill.  I also adjusted the VSS Skin Template considerably. I put a "steelblue" colour in both Tint and VSS and bumped PM:Boost to 1.5.

I left a comment in your gallery.  Spectacular.

Thank you hborre!  I´m hoping that I´m sailing out of a huge block that I've been in for a looong time :)

Attached Link: Portrait1

Thanks again for the help BB..

It does pay to have a very good texture map for close-ups.  Beautiful image.

That came out really well. The hair is good, but the face is so good, the hair looks bad!

Quote - Thought I'd share this, I finally finished one using the Soft Studio lights. Did some postwork in PS , added the DOF and some level adjustments - I think it came out pretty good.

Thanks again for the help BB..

Is that one of Danae's textures? It looks really good.

Thanks for the comments. The hair is the main reason I added the dof in PS, the straight render looked good but the hair took it down a notch - had to blur some of it out.

JWFokker, yes its Milan, its the only really good texture I have, as I'm finding out good textures are hard to come by. Any other good textures out there you guys recommend ? I'm searching thru promos, but the quality of most promo renders is not that great so its hard to tell how good the textures really are, any suggestions would be appreciated.

Thx

 Assassin Angel v4 and Vanessa v4 both at daz, and by the same person, are excellent. I don't use the face morphs but the textures look wonderful with VSS.