I've been looking into this recently, and a little research suggests that the size of the frame buffer is an important factor to consider when rendering a high resolution image using mental ray for Maya.
While there are no explicit limits for the resolution parameter, it's important to understand how mental ray caches its frame buffers.
RC 0.2 warn 082059: camera x resolution -25536, increased to 1
The reason could well be linked to the amount of memory available to store your frame buffers.
By default, mental ray wants to store - or cache - each frame buffer in a .map file on your hard drive, and there is a 2GB limit on the size of each frame buffer files . You therefore have to ensure that each frame buffer comes in at less than 2 GB….
So if your primary frame buffer is RGBA 8bit, your max resolution is around 23000 x 23000 (as per the mental ray docs, in “known limitations”), and if your frame buffer is RGBA 32 bit, then you are limited to around 11180 x 11180.
However, you can change your frame buffer cache mechanism in Maya on the mentalrayGlobals node, under Extra Attributes, or using the MEL command:
setAttr mentalrayGlobals.frameBufferMode 0;
The values for the attribute are:
- 0 = All in Memory (Off);
- 1 = Full Disk Caching Using Memory Mapping (On);
- 2 = Partial Disk Caching Using Tiles (Cache)
For users of mental ray Standalone, this is equivalent to setting the flag "-fb_virtual".
The docs say that this parameter "controls storage of frame buffers in files on disk to conserve memory. Default is On".
If Frame Buffer Mode is set to All in Memory (Off), then the maximum framebuffer size is 4GB using internal memory.
The third option: Partial Disk Caching Using Tiles (Cache) option "enables frame buffer caching, which only stores frame buffer fragments in disk files on demand".
I hope you find this information useful.
Almost forgot: thanks to Ash and Eric B for their input