Wednesday, 7 August 2013

Bitmap tip

Who'd have thought something that's been there all along could improve your renderings so much?..

For a couple of years I had found myself in the same situation every time when rendering an image of, let's say, a building. The dirt/tarmac/etc on the floor of the foreground would always appear to have a slightly blurry look, and not the sharpness I'd have expected given the resolution of the bitmaps being used.

I then found that under bitmap filtering I could reduce the blur using a numerical value, though reducing it too much created strange artefacts in the material editor; thus leading me to the assumption that it would also render with artefacts too. It turns out however that this is not the case, and turning off filtering altogether has several major advantages when using VRay (I've not tried it in Mental Ray, but I'd imagine that it probably gives similar results).

Firstly you get improved image quality due to the fact that max isn't doing the filtering (which appears to be the same kind of filtering you get in video games, at a glance); VRay's anti-aliasing filter will take over to remove noise/moire/roughness on parts of the texture that breach its noise threshold (often textures that are at a glancing angle or in the distance, as this is where max would usually filter). This means two things, firstly it means that VRay does in fact have to work a little harder to cope with this additional noise, but it also means that the quality is dramatically improved too.

Secondly when you use this technique with displacement it also has the added effect of speeding it up, and then finally we get onto opacity maps which again you get a fairly substantial increase in rendering speed - so all of those billion poly trees you want to render will come out in a flash, all controlled entirely by your anti-aliasing settings.

Here's an example of the difference in speed you can get from disabling filtering on your opacity maps:


But disabling filtering on massive scenes is quite a chore, surely? Well no, because this handy little script can take control of all your filtering needs;

The only thing I would mention with this script is that sometimes it doesn't work on bitmaps that are "embedded" for lack of better words within other maps such as a noise map, or forest colour. I haven't done enough work though to be able to compile a list of things that it doesn't work with.

I shall endeavour to post some test renders with render-times just to prove a point. I promise you will see the difference in quality!

Happy filtering.

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