I have been spending a lot of time on this chest lately. It's the blend of
two hobbies, i.e. bitfiddling and woodworking. The workshop is getting
pretty cold this time of year so this chest may not be a reality for awhile.
I have the design totally animated so I can modify most of the dimensions
and it automatically adjusts everything.

I do have a question - I love the woodgrains, but I have never been quite
satisfied with the lighting effects. This object is 24 x 18 units around the
origin and drops Y*-36 and I have been fiddling with global settings and
lighting.

Some softer lighting to create more gentle shadows but still **bright**
diffused lighting is what I think I'd like ( I seem to have trouble getting
*enough* light on the subject)

Suggestions??

Here's what I currently have:


// place all settings of globally influenced features here
global_settings { assumed_gamma 1.8 }
// Have tried ranges of 1.5 to 2.2


light_source {
  < -100, 20, -50>       // light's position (translated below)
    color rgb <2,2,2>      // light's color
}

light_source {
  < 100, 20, -50>       // light's position (translated below)
    color rgb <2,2,2>    // light's color
}

light_source {
  <   0,  20, -200>       // light's position (translated below)
    color rgb <1.0,1.0,1.0>    // light's color
}

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Attachments:
Download 'Chest36x24x18-Leg416.jpg' (149 KB)

Preview of image 'Chest36x24x18-Leg416.jpg'

"Stephen" <sig### [at] shawca> wrote in message
news:41c3cd16@news.povray.org
> I have been spending a lot of time on this chest lately. It's the
> blend of two hobbies, i.e. bitfiddling and woodworking. The
> workshop is getting pretty cold this time of year so this chest may
> not be a reality for awhile. I have the design totally animated so
> I can modify most of the dimensions and it automatically adjusts
> everything.
>
> I do have a question - I love the woodgrains, but I have never been
> quite satisfied with the lighting effects. This object is 24 x 18
> units around the origin and drops Y*-36 and I have been fiddling
> with global settings and lighting.
>
> Some softer lighting to create more gentle shadows but still
> **bright** diffused lighting is what I think I'd like ( I seem to
> have trouble getting *enough* light on the subject)
>
> Suggestions??

Area light(s)

Post a reply to this message

"Stephen" <sig### [at] shawca> wrote:

> I do have a question - I love the woodgrains, but I have never been quite
> satisfied with the lighting effects. This object is 24 x 18 units around the
> origin and drops Y*-36 and I have been fiddling with global settings and
> lighting.

Hi Stephen, I'm also a beginner in POV-Ray.... but I've been working in
graphics in general... I hope I can be helpful.


>
> Some softer lighting to create more gentle shadows but still **bright**
> diffused lighting is what I think I'd like ( I seem to have trouble getting
> *enough* light on the subject)
>
> Suggestions??

Try this:  1: restore lighting to <1, 1, 1> everywhere and raise the diffuse
values for the objeccts.  2: Change the background light, because the
"black" is dominating everything and making the subject look dark.  I
noticed that many modellers like to put their subject on a white plane, and
I think it's because the white plane can reflect light, reducing the
hardness of shadows.  3: You can experiment with ambient if the subject is
still too dark in the shadows.

>
> Here's what I currently have:
>
>
> // place all settings of globally influenced features here
> global_settings { assumed_gamma 1.8 }
> // Have tried ranges of 1.5 to 2.2

Restore gamma to 2.2 to bring out the color.  1.8 seems ok, it will brighten
the subject without taking away too much color.  (However just for
experiment, try a gamma of 1.0 just once, to see if the wood becomes more
realistic.)

Also note that one of the legs of this furniture is very different.

Finally, there's nice wood in the woodbox sample when you install POV-Ray.
You might borrow some code from there.

Post a reply to this message

What you have here is great, yet overwhelmed with light (I believe).

Somewhere on the Pov server is a gif image used to adjust your monitor for 
the proper gamma value. You can ask about it in povray.general, or if I come 
across it later I'll reply again here. Whichever value it comes up with is 
the value you want to use as the assumed gamma.

White backgrounds are good, too. You don't have to use white, though. I 
prefer to think of the background as the environment in which I would 
normally find the object I am rendering. I use white only after I have 
control of the lighting. However, I do use a sky_sphere rather than a plane.

sky_sphere { pigment { gradient y poly_wave 1.5 color_map {
      [0 color rgb .99]
      [.35 color rgb 1.33] } } }

This isn't written in stone, though, so even if it gives you good results 
continue to experiment. I'm one guy that always breaks the rules in search 
of my personal 'artistic impression.'

For wod, though, I think I'd be going in a different direction. I'd probably 
use a slightly blue, or even yellow light source. But again, this is not as 
important as control of the light is. In your image I see the light_source 
as overwhelming the object. Move the light back by at least 350 units in 
every direction. That's a good place to start, anyway. If you need a light 
in one area in order to bring out some details, don't be afraid to add a 
diminished light value that is also shadowless (so it doesn't leave clues as 
to its presence. Something like:

light_source { <#,#,#> rgb .3 shadowless }

Good luck.

- Grim

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You can find the image I spoke of included with the Pov-Ray documents under 
display_gamma (Section 3.1.2.3.2  Setting your Display Gamma).

- Grim

Post a reply to this message

I found the Gamma image in the help text and will try that out (again).

I have used a white background or black background for simplicity to post
the pictures. Typically my favourite is the reflective coppery one from the
"WOODBOX.POV" in the samples, but it takes longer to render during
develoment.

Perhaps what I'm not so sure about is the comment to:
>> Move the light back by at least 350 units in ...

as I'm unclear as to why that looks a bit better. Given my measurements of a
table sized 20x30, then 350 units would be about 30 feet away - I guess that
makes sense, but I had some lights about 200 units. Is there a technical
reason for the lights to be further way?

Any additional comments or suggestions welcome.
-- 

Stephen
and
Kathie
(S+K)
"GrimDude" <a36### [at] bellsouthnet> wrote in message
news:41c44f76$1@news.povray.org...
> What you have here is great, yet overwhelmed with light (I believe).
>
> Somewhere on the Pov server is a gif image used to adjust your monitor for
> the proper gamma value. You can ask about it in povray.general, or if I
come
> across it later I'll reply again here. Whichever value it comes up with is
> the value you want to use as the assumed gamma.
>
> White backgrounds are good, too. You don't have to use white, though. I
> prefer to think of the background as the environment in which I would
> normally find the object I am rendering. I use white only after I have
> control of the lighting. However, I do use a sky_sphere rather than a
plane.
>
> sky_sphere { pigment { gradient y poly_wave 1.5 color_map {
>       [0 color rgb .99]
>       [.35 color rgb 1.33] } } }
>
> This isn't written in stone, though, so even if it gives you good results
> continue to experiment. I'm one guy that always breaks the rules in search
> of my personal 'artistic impression.'
>
> For wod, though, I think I'd be going in a different direction. I'd
probably
> use a slightly blue, or even yellow light source. But again, this is not
as
> important as control of the light is. In your image I see the light_source
> as overwhelming the object. Move the light back by at least 350 units in
> every direction. That's a good place to start, anyway. If you need a light
> in one area in order to bring out some details, don't be afraid to add a
> diminished light value that is also shadowless (so it doesn't leave clues
as
> to its presence. Something like:
>
> light_source { <#,#,#> rgb .3 shadowless }
>
> Good luck.
>
> - Grim
>
>

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Units are basically arbitrary. What I meant was to move the lights further 
away. Try something like"

light_source { <-350,350,-475> color rgb 1 }

and if you insist upon using three lights, just sapce them apart on the 
x-axis, or something similar. You won't see the swamping of light upon a 
object and overall intensity should appear diminished. The reason for using 
greater separation distances is to aid in the control of lighting. Lighting 
will appear to be much more realistic without having to rely upon parallel 
rays, for instance.

Experiment! You can't break anything that I know of! I can't wait to see 
your results!

- Grim

Post a reply to this message

Thanks for the feedback.

But the reason I was using three lights was to get **enough** illumination.
Just one light doesn't seem to cut it, so I'm wondering if there's something
basically wrong in my approach or system.

So the question would be - in any typically arbitrary scene such as modeling
a TV or a plant or a table or desk, can you illuminate the scene with one
light source which would approximately simulate one 100W lightbulb in the
room, at 6-18 feet away?

My answer would be - nope- need multiple lights. What's that tell you?


I'll try the gamma correction right now.

Stephen

-- 
"GrimDude" <a36### [at] bellsouthnet> wrote in message
news:41c4ee3f$1@news.povray.org...
> Units are basically arbitrary. What I meant was to move the lights further
> away. Try something like"
>
> light_source { <-350,350,-475> color rgb 1 }
>
> and if you insist upon using three lights, just sapce them apart on the
> x-axis, or something similar. You won't see the swamping of light upon a
> object and overall intensity should appear diminished. The reason for
using
> greater separation distances is to aid in the control of lighting.
Lighting
> will appear to be much more realistic without having to rely upon parallel
> rays, for instance.
>
> Experiment! You can't break anything that I know of! I can't wait to see
> your results!
>
> - Grim
>
>

Post a reply to this message

Stephen wrote:
> Thanks for the feedback.
> 
> But the reason I was using three lights was to get **enough** illumination.
> Just one light doesn't seem to cut it, so I'm wondering if there's something
> basically wrong in my approach or system.
> 
> So the question would be - in any typically arbitrary scene such as modeling
> a TV or a plant or a table or desk, can you illuminate the scene with one
> light source which would approximately simulate one 100W lightbulb in the
> room, at 6-18 feet away?
> 
> My answer would be - nope- need multiple lights. What's that tell you?
> 
> 
> I'll try the gamma correction right now.

 From an advanced newbie...

Realistically simulating lamplight (or any other kind of real-world 
light source) in POV-Ray is a good deal more complicated than simply 
defining a light source at a certain distance, with a certain 
value/intensity, and hoping for the best.

First of all, a default light source has no falloff. The light rays will 
be equally bright whether they're 100 units away or 10,000 units. The 
only difference is how many rays hit the object (since a default light 
source emits light in all directions, placing the light source very far 
away spreads the rays out more, thereby making an object *appear* 
darker). In reality, it's just receiving fewer beams.

However, putting your light source very close isn't always the answer 
either, since you'll have high concentrations of light beams in a small 
area, causing washed-out spots.

GrimDude is simply saying that you'll get smoother coverage with your 
lights - the rays will be more spread-out, reducing blown highlights - 
by moving your light sources farther away. I would have said exactly the 
same thing myself if I had noticed the problem (it really didn't strike 
me). When I'm not trying to achieve photorealism, I quite often put my 
lights 500+ units away, even if my object is only a few units each 
dimension. If I had a very large object, eg. 30x30x30, I would probably 
put my lights even farther, such as 800. That's just how I tend to 
operate, however. If you really want a photorealistic effect, the rules 
all change.

There are ways to make the light sources behave realistically. POV-Ray 
supports light falloff and fading, which, when set properly (an area I 
can't advise on, unfortunately) can produce quite realistic results. If 
you want to look these up, look for the 'falloff' and 'fade_distance' 
keywords in the Help file.

Incidentally, Jaime Vives Piqueres has done some research into the 
physical properties of light and has created some macros for realistic 
light simulation. I am still learning how to use them myself, but you 
might find them interesting. http://ignorancia.org/lightsys.php

Hope this helps somehow. As long as you keep in mind that I'm not an 
expert and thus take all this with a grain of salt, I think you'll be 
okay. :)

~Mike

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Mike Thorn wrote:

| First of all, a default light source has no falloff. The light rays
will
| be equally bright whether they're 100 units away or 10,000 units. The
| only difference is how many rays hit the object (since a default light
| source emits light in all directions, placing the light source very
far
| away spreads the rays out more, thereby making an object *appear*
| darker). In reality, it's just receiving fewer beams.
|
	There appears to be a small misunderstanding on how light sources
work here. For regular light sources (ie not area lights), there is
exactly one ray of light for each point of your object no matter what
the distance to the light source. If you don't use anything special
like falloff or semi-transparent objects, that light ray will have
the exact intensity specified in the light source definition. As a
result, the object will have about the same brightness no matter how
far the light source is situated. However the brightness is affected
by the angle between the light ray and the surface: it is maximal if
the ray hits the surface straight on and diminishes to zero when the
ray is nearly parallel to the surface. This is why placing the light
source farther away makes for more uniform illumination: the farther
away, the closer to parallel the rays.

	Incidentally, your description ("rays spread out more") is more or
less what happens in real life and the reason why real light sources
get dimmer with distance.

| There are ways to make the light sources behave realistically. POV-Ray
| supports light falloff and fading, which, when set properly (an area I
| can't advise on, unfortunately) can produce quite realistic
results. If
| you want to look these up, look for the 'falloff' and 'fade_distance'
| keywords in the Help file.
|
	To get realistic results, you should use "fade_power 2" and set the
fade_distance to the size of your light bulb, then give a *very* high
value for light intensity (you do know that intensity is not
constrained to the 0-1 range, don't you? In fact you can even create
negative light sources wich allows for some interresting special
effects...). 'falloff' has nothing to do with it and has meaning only
with spotlights and cylindrical lights: it defines how much light you
get as you get further from the center of the beam.

	BTW, if you intend to use cylindrical lights, read the doc
carefully, they probably don't do what you think. To get the right
effect, you'll have to look at the 'parallel' keyword :p

		Jerome

- --
******************************
*      Jerome M. Berger      *
* mailto:jbe### [at] ifrancecom *
*  http://jeberger.free.fr/  *
******************************
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