What is mental ray rendering and why would it produce a black image
Mental ray is used in Autodesk 3D Studio Max (Autodesk 3ds Max), Autodesk Maya, Softimage|XSI and in many other software packages.
Mental ray is a 3D rendering application that produces photo-realistic images. Mental ray renders photorealistic images by simulating the physics of light, including reflection and refraction, global illumination and caustics. To achieve photo-realistic images, mental ray uses a set of algorithms to simulate how light reacts as it travels from one object to another.
Mental ray Community Wiki – page Mental ray Rigging and Rendering
Shading Language: shadertoy.com/shaders/view/103369?count=50
“mental ray rendering” : http://www.mentalray.com/blog/managing-ray-rendering
“what is mental ray rendering and why would it produce a black image” : http://validator.w3.org/check?uri=www.mentalray.com&ver=7
The three most common causes of mental ray rendering black images
The main reason why mental ray renders black images is because of its memory management! By default mental ray uses a technique called adaptive culling. Many users do not know what this is and how it works, so let me explain it here briefly. Culling is the process of removing (that is “culling”) objects that are hidden away from the viewer in order to speed up image rendering. Adaptive culling takes this culling a step further. It only renders what is visible on the screen, so interior walls and ceilings disappear. This can be a great timesaver, but can also give some surprising results when they disappear.
Another common problem is scene origin. mental ray does not have a notion of absolute coordinates. Instead it has a notion of relative coordinates that are defined by using the origin of the current camera as a base point. If you change this base point by zooming in or out then all objects that were originally seen from the center will be rendered from the new center point instead (with some exceptions, such as text and cameras). This can lead to unexpected results, for example when rendering interiors with moving camera’s (such as cars or helicopters).
Here’s a screenshot of the example scene (the camera in the center is a little bit zoomed in and rotated down):
How to troubleshoot and fix the problem
If this is the first time you are seeing a black image in your scene, you might want to check to see if you have set mental ray rendering to “High” or “Low”. If your imagery is in Camera view, then the problem is most likely that the mental ray camera shadow maps are not looping (compared to what the ray-traced shadows of your scene are doing). The memory settings for these two settings can be found in the Settings Inspector. Both settings can be found in the section named [Mental Ray] under [Quality]:
Shadows : this is what matter ray shadows look like when rendered at the lowest quality setting in the Render Settings dialog. If you are rendering a scene that has a lot of geometry, mental ray will use up all your system memory and/or swap space very quickly. Therefore, if you’re rendering a high resolution scene with many large buildings, you might want to render in low quality mode until you have one or two large scenes that can be rendered with not too many rays and thus not too much memory (and disk) consumption.
Camera : this is what matter ray shadows look like when rendered at the highest quality setting in the Render Settings dialog. If you are rendering a scene that has a lot of geometry, mental ray will use up all your system memory and/or swap space very quickly. Therefore, if you’re rendering a large scene with many large buildings, you might want to render in high quality mode until you have one or two large scenes that can be rendered with not too many rays and thus not too much memory (and disk) consumption.
settings numbers: [low] is 0, and [high] is 1 (there are other settings, 0-7). The amount of memory currently being used in the system can be found in the internal TempRatio field from the MSysAbout() function.
