View Full Version : How to blur the image BEHIND a transparent object?

08 August 2004, 05:16 PM
What I want to simulate is for example the effect of thin cloth, which - if you look through it - would slightly blur the image behind it. I guess there are ways to do this with MentalRay or Brazil, and I KNOW that it can be done by rendering multiple passes. But I would be interested in a way to do it in a single pass, and with MAX's Scanline renderer.

MAX's own blur effect allows to specify the area to be blurred via material- and object-IDs, but by this the blur of course extends beyond the edges of the respective object, plus the object itself (for example a plane mapped with some fabric-texture) gets blurred too.

The frst problem mentioned appears to be fixable, since I've seen a render-effect plugin (can't remember where) that allows to blur the image based on an object ID, and makes the blur being masked to "stay inside" the area to be affected. But even this plugin has the problem of the original object getting blurred too, so this wouldn't work for textured objects.

I guess it would be required for the image to be rendered in 2 layers internally, and then composing the object causing the blur (in this case the fabric) on top of the partially blurred background.

It would be even better to have a plugin, that allows to apply all available render effects, based on their position in the scene, relative to other objects (or pixels). So that you can, for example, not only blur the image behind the fabric, but change its colors and contrast as well. So instead of just limiting a render-effect to material-IDs, object IDs, Z-position, you could also limit an effect to something like "behind object x" or stuff like that.

Would this be possible?

09 September 2004, 02:09 PM
Yeah, this has been a problem I have come across loads of times. I haven't found a perfect fix yet but try the "Motion Blur" in the "Effect" menu.

Swith "work with transparency" ON of course ;)

Sometimes it seems to work but it depends how fast the foreground object is moving.


09 September 2004, 01:10 AM
may be I didn't quite understand your problem.'s may be here : ?? (in russian tho')
I think you can test these 2 plugs : Surface Blur & Throughout (or something like).

09 September 2004, 02:21 AM
Yeah, that's the plugin I was talking about... it comes really close, but unfortunately it blurs the entire foreground object. So if you have a texture on your "curtain" (or whatever you want to use this effect for) it gets blurred too.

I found that using a "Thin Wall Refraction" in the Refraction-slot kinda works... although with basically no control, except for the general blur size (but with no way to decide, that faces closer to the "curtain" get blurred more then faces further away).

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