3ds Max: ambient occlusion map is blocky regardless of settings

Graphics Lighting & Global Illumination
1

When I render an ambient occlusion map to a texture in 3ds Max (using the mental ray renderer), the resulting image is always composed of blocks of colour 2-by-2 pixels in size (see images below). (Note that this is different from the grainy effect associated with using a low number of samples when rendering the AO.)

1215784--49683--$Plane001Ambient Occlusion MR.png
Actual AO map (I used a low number of samples when rendering it to highlight the blocky effect).

1215784--49684--$Ambient occlusion zoomed in.png
Zoomed-in portion of AO map with some individual pixels re-coloured to highlight blocks.

This effect occurs regardless of what the output map size, the number of samples, or any of the other ambient occlusion parameters are set to. Is there another rendering setting that needs to be changed to remove this blocky effect?

Note: I’ve also posted this question on the 3ds Max forums here, but as of yet no one has responded.

2

Download textools from scriptspot.com. The tool makes better maps.

3

Is your resolution low? That would do it.

4

I’d rather not rely on functionality outside of that already provided by 3ds Max itself (for portability reasons), but I’ll look into textools.

Larvantholos, which resolution are you referring to? If you mean the output map size: the effect occurs independently of the resolution of the rendered texture (for example, a 128-by-128 render and a 1024-by-1024 render will both be composed of 2-by-2 blocks).