Area lights shadows look like "steps"

[David Saber]

Hi all,

Please check this picture of a coffee cup, rendered in its own shadow pass:
http://david.saber.free.fr/bazaar/xsi/Softimage_AreaLights_Rendering_Problem.jpg


As you can see, the shadows are not soft, they look weird, like
"stepped". I tweaked some shadow and area light settings, but I didn't
find the right settings yet I guess...

Current area light settings:
- Geometry = disc
- Samples U&V = 15
- Low samples level = 0
- Low samples U&V = 2
- Scaling X, Y & Z = 10
Render region's shadow settings:
- Type = segmented.

Thanks for the help!!!
David

[Jason S]

That stepping always occurs, (revealing object polygons without
"smoothing")
happenning at the lit/shaded threshold of objects.

But normally isn't visible, as it happens slightly beyond the maximum
reach of the light on an object
(will show-up in shadow only passes)

And should similarly (normally) become invisible once you comp your
shadows in, on a pass with that light only.

Of course if you comp that on on the final with other light sources
you'll see the stepping,
in that is the case, you can turn off "cast shadows on visible faces"
and voila!

On 03/08/14 14:01, David Saber wrote:
> Hi all,
>
> Please check this picture of a coffee cup, rendered in its own shadow
> pass:
> http://david.saber.free.fr/bazaar/xsi/Softimage_AreaLights_Rendering_Problem.jpg
>
>
> As you can see, the shadows are not soft, they look weird, like
> "stepped". I tweaked some shadow and area light settings, but I didn't
> find the right settings yet I guess...
>
>

[David Saber]

Hello Jason,
Thanks for the help.

The steeping is well visible in my render pass' camera, not only in the
threshold but on large parts of the roundness of objects. So as I use
this shadow pass as an alpha in composting, it's annoying.

But your post made me think of other options to tweak:
- In Geometry approximation > Poly mesh > I increased the subdiv level
from 2 to 3 and got smaller "steps".
- In Geometry approximation > Poly mesh > I increased the discontinuity
angle from 60 to 120 and got more softness.
- In the light settings > soft light > raytraced soft shadows > I set
it to 3 and 15 and got a bit more softness, but it seriously increased
rendering time.

What bugs me is that the steps are still here. Smaller and softer but
still here.
By the way, I didn't find the option to turn off "cast shadows on
visible faces", could you help me on that?

Thanks,
David

[Alexander Akbarov]

I'm not sure which passes(channels) you rendering except this one, but I think you can get your shadow pass from your beauty's pass lighting channel, if you render separate pass with lighting only but without shadows and an albedo pass.

[Jason S]

Indeed about channels,

But also, even if you'd get a perfectly smooth lit/shaded gradient,
unless you are comping on another pass with that light only,
there would still remain that "moonlike" abrupt lit to shaded transition
which would show-up on your fully lit model.

Which is that makes the cast shadows on visible faces important.

Disabling it still allows for self-shadowing, but only renders drop shadows,
while leaving the the darkness in shaded areas up to the illumination shader.

That option is in the Shadow shader and perhaps elsewhere (you may also want to inverse it)

And along the same lines as Alexandre suggested, you can pipe it into a "store in channel"
to output it at the same time as your beauty and/or other AOVs.

Cheers!

  

[David Saber]

Hey guys,

Thanks for the suggestions, which got me interested in render channels.
Previously, I was rendering with a pure pass workflow.
I read the doc about channels but there is no example on how to use
custom channels. So now I have more questions if you don't mind : )

But before that, here is what I'm doing:
http://david.saber.free.fr/bazaar/xsi/cups_fxtree.jpg
The pass and light setup is pretty simple:
My beauty pass has overrides that cancel area light and drop shadows.
In the FXtree, I mix my beauty and FG pass, then use the shadow pass
(self shadow + drop shadow) to put the same , but darkened, FG pass in
the dark areas of the cups.

In the beauty pass, it is true that when I re-enable the area light, I
do not see any "steps". Can I get the same result as the shadow pass,
with channels? I didn't manage to set up a shadow channel, how is it
done? The ideal thing would be to have the self shadow and the drop
shadow in one single rendered image, just like the shadow pass does.

More questions:
- Alexander, you mentioned "lighting channel", is this the key to a
shadow channel? Where is it found?
- You also mentioned an "albedo pass", I guess it's something that just
outputs color? Is this the "color" channel? When I tried to render a
color channel, the result was all black, why?
- What's an "AOV"?

Thanks for sharing your knowledge. Long live this list and long live
Softimage!
David

[Alexander Akbarov]

Your beauty pass composed from several basic channels: diffuse (or some renderers call it lighting, e.g. vray ), reflection, refraction, specular. So lighting channel it is your beauty pass -(minus) reflection - refraction - specular. I assume that you are using architectural shader and don't use GI or Self Illumination. And you can find it in the scene render channels. Albedo color this is flat color - just your textures without any lighting involved, there is some almost automatic methods to get it, without messing with partitions. I will write it here if you are interested. Not sure what "color channel" you mean, what shader you are using is there any mix nodes in the Surface port? AOV it's just fancy name of render channel I guess )

[David Saber]

Hello Alexander,

I played again with channels and got a better understanding of it thanks
to your help and to Ola's great blog
http://caffeineabuse.blogspot.fr/2012/03/using-render-channels-in-softimage.html
.

So here is my last attempt at having both self shadow and drop shadow in
one single rendered image:
http://david.saber.free.fr/bazaar/xsi/ShadowNodeProblem.jpg
Bugger! It's the same situation as with the shadow pass :( So I guess
the problem lies in the render tree shadow node.
Isn't there any way to smooth the self shadow? I tried 'simple shadow"
but it doesn't work.

To answer your question:
- My shaders are very simple, no architectural. Just image nodes in
phongs, basically.
- As for the albedo pass, to get it, I assume you just put a constant
material on a whole partition ?

Regards,
Dave

[Oscar Juarez]

As far as I know, that has always been a problem with the Shadow node, I think when I've had to use the shadow node, I turn off shadow cast on visible faces, I basically have used this as a shadow catcher, why you need the shadow cast on visible faces? that should come out with your shading and lighting doesn't it?

[David Saber]

Hello Oscar, thanks for your answer!
Well, if you look at my FX tree:
http://david.saber.free.fr/bazaar/xsi/cups_fxtree.jpg
I also have a final gathering pass that I darken through color correct.
Then I input it in the shadow areas (self shadow + drop shadow).
In my beauty pass, the shadow on visible faces is simply black. Perhaps
I'm wrong, but I think it would be better if the shadow on visible face
(self shadow) should be lit by this darkened FG pass, instead of being
just black... What do you think ??
David

[Oscar Juarez]

Let me see if I understood your rendertree, you are rendering your beauty without any shadows right? then an FG pass which you add to the beauty pass two times, one normal and one darkened and masked with the shadow pass.

It's being a while since I've rendered in this kind of components, but light should be treated as an additive thing. I would render the beauty with shadows, and add (plus) the final gathering to that pass, if you want to change the color and intensity only for the shadows I think I would resort to making a new pass, override the surface port of all the objects and connect a white lambert. Then you got your shadows and self-shadows without resorting to the shadow shader.

I mean it's not physically correct but for your purposes might work.

[David Saber]

Yes, you got my rendertree correctly.
I guessed I had to use a lambert at the end! :) A white lambert isn't
exactly the same effect as the shadow pass, and the shadow pass is quick
to setup, but because of the visible faces problems, I'll use white
lamberts from now on.
So thank you Oscar for your help!
Greetings,
David