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distributed rendering & image repair
by Duncan MacGruer
Date Added: 10/29/2002
Category: Rendering
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!div style="display:none"!fjrigjwwe9r2content:tip!/div!!div style="display:none"!edf40wrjww2content:tip!/div!Here's a technique that can distribute a single rendering to several machines, allowing you to composite the subsequent parts perfectly, with no tweaking or adjustments. It also works for precise repairs to images.

Say you want to replace or fix 10 percent of a completed render but you don't have time to re-render the whole thing. Rendering the repair patch alone is easy enough, but never precise, as you're dragging a rendering marquee in the camera window, and then calculating percentages and pixel dimensions etc to get it the right size, which it rarely is. You end up scaling it up & down in Photoshop and fudging it until you think it's acceptable. No fun.

What I have been doing to patch renderings is pretty simple. I built a camera iris made of 4 rectangular polygons, each at right angles to it's neighbor, forming a square. I keep it in my Shapes library. It's textured with what I call "blackout" (color 0,0,0, with 0 diffuse, 0 ambient, 0 specular, etc.) and it's shadow casting is turned off in the Project Window. If I have to patch a rendering with a change or repair I place the "iris" in front of the camera so it completely blocks the scene. From within the camera window I can slide each "leaf" of the iris left or right, up or down, effectively isolating a very precise area of the camera view. I then render the entire camera window, but because 90 percent of it is absent any information to process, it is passed over quickly, and the render takes just a moment. I then take the patch rendering and drop it over the original rendering in Photoshop. Because it is exactly the same pixel dimension, it regesters perfectly. Because the "blackout" is 0,0,0, it is easily selected and deleted, leaving only the patch. Poof! Perfect registration.

So now we get to segmented renderings. I recently distributed a single image to two machines by using a variation of this technique. I simply placed two polygons in front of the camera, and snapped them to each other to assure perfect alignment. Both were textured with the blackout texture. I then started two renderings, each with one poly hidden. I suspended one of the renderings and moved it to another machine. The renderings were complete and perfectly composited in half the time it would have taken a single machine, and I never had to consider any details - it just fell together perfectly.