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Iray lights - emitters casting unwanted shadows and reflections

andya_b341b7c5f5andya_b341b7c5f5 Posts: 694
in Technical Help (nuts n bolts)

Suppose you have a two photometric lights, both with Light Geometry set to sphere, on opposite sides of a scene - not quite opposite, but close enough such that one is casting a circular shadow on a wall behind it from the light of the other.  There seems to be no way to prevent this shadow-casting, except to set the geometry to point - is that right?  It seems pretty limiting that there is no 'cast no shadows' option on a thing which is not visible in the render in spite of being 'in shot'.

Similar issue with reflection: lights with sphere geometry that is not point can be seen as circular reflections on glass etc.  So, same puzzle: is the only way to stop this to set the geometry to point?  Feels like logically if you can't see the emitter in the render, you shouldn't see its reflection either.

I'd prefer not to set the lights all to point geometry as it makes the shadows (the wanted ones!) sharper than I would like.

Comments

  • SzarkSzark Posts: 10,634

    This is way Iray is called Photoreal, no "cast no shadows" as we cannot do that in the real world. This is the major difference between 3Delight and Iray etc. One has freedom and one is constrained in terms of flexibility.

  • ToborTobor Posts: 2,300

    I haven't done any photo studio work in years, but when I did, I'd get shadows cast from lights and light stands if I didn't carefully place them. I guess that's a limitation of nature, but as Pete sez, it's how it all works.

    Have you tried Interactive mode render? There you can have more control over shadows. You are a little more limited in what can be rendered -- I recall you cannot use more than 16 lights, and emitters created from primitive gemoetry will look lit, but won't illuminate the scene. However, nearly all the shaders work the same between the two modes. Here's a quick write-up I did a while back that compares the two modes:

    http://www.daz3d.com/forums/discussion/59450/iray-render-mode-comparison

  • andya_b341b7c5f5andya_b341b7c5f5 Posts: 694

    Thanks for the input Szark and Tobor.  I've had a look at using interactive mode for Iray - I think am losing more than I gain, so it looks as if I will have to work around these 'features'.  In this case I have moved that light that was causing the geometry of the other light to cast a shadow so that the shadow is out of view, and moved the camera a bit so that the reflection in the glass is also out of shot.

  • SzarkSzark Posts: 10,634

    I haven't played with Light Catagories and tagging yet and I am not to sure if we can tag items not to recieve light from a particalar light or lights.

  • Steven-VSteven-V Posts: 727

    One work-around for this is to render multiple times with different lights turned on and off, and then pull the images all into Photoshop as individual layers. Then screen them all and mess with the opacity until you are happy with the result.

  • HeraHera Posts: 1,957
    edited December 2015

    I have a similar problem, I have two items which are not supposed to cast shadows, as they are light themselves. Rays of Starwars-esque lightsabres in this case, made by cylinder primitives which have been textured with the iray blue neon. But in spite of having "cast shadows" set to off those rays are still casting shadows when I render in Iray. What will I have to do to having them NOT casting shadows?

     

     

    Post edited by Hera on
  • SzarkSzark Posts: 10,634

    Use 3delight instead as Iray is a realistic render engine and cast shadow off will not work as per my post second from the top..

  • HeraHera Posts: 1,957

    Then I guess there's time to create something like "light objects" to use for flames, beams, sparks and similar things to get around this problem.

  • ToborTobor Posts: 2,300
    Hera said:

    But in spite of having "cast shadows" set to off those rays are still casting shadows when I render in Iray.

    Iray Photoreal does not support a control for casting shadows. So, you are either using Iray in Interactive mode, or you've tried to "trick" Iray Photoreal into turning off shadows by showing hidden parameters, and turning off the shadowcast option. The latter does not work -- the parameter is hidden for a reason.

    If you wish to experiment with shadowcasting, first change the render mode to Interactive. Then experiment from there.

    You might have some success with emitting objects and shadows by setting their Opacity Cutout to 0.0001. It will still glow, but the solid geometry that makes up the object will not be visible. You get shadows from geometries because opaque things block light.

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