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Specifies the rendering engine to use for rendering. The available options are :

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the 'REYES' based algorithm and 'Path Tracer' for the ray tracing based algorithm. A discussion of the Pros and Cons of each is presented in the last section of this page.

Progressive Refinement

This option is only available when using the 'Path Tracer' Render Engine. When this toggle is turned on, the rendering rapidly shows a coarse image and then refines it progressively until completed. This option is effective only for images outputted directly to a window on screen (i.e. to the Maya Render View or to 3Delight i-Display). During batch rendering (i.e. when using Maya Batch) this option is ignored.

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This option controls if the RIB file will be compressed, producing a smaller file. By default this option is off.

Pros and Cons of REYES vs Path Tracing

REYES

Pros:

• Extremely efficient rendition curved surfaces of average to large size; that is surfaces covering more than a few pixels on the image.
• High quality motion blur and depth of field are extremely fast. This is because the shading calculation is decoupled from hiding calculation.
• Displacements are rendered at a lesser cost than in path tracing (micro-polygons).
• Efficient at rendering fluids because of screen space under-sampling.
• Performance almost independent of oversampling (pixel samples). This makes it easy (and fast) to render images without noise and without aliasing.

Cons:

• Looses performance when rendering densely tessellated geometry.
• Not suited for rendering scenes with high "pixel complexity" (e.g. a crowd seen from afar).
• Motion blur shading is only an approximation. For example, a spinning wheel will have its specular highlight blurred along with other details on the wheel, whereas the highlight should remain sharp.
• Takes more memory when used alongside ray tracing (for GI for example). This happens because we need ray tracing structures alongside REYES structures.

Path Tracing

Pros:

• Good at rendering densely tessellated geometry and dense scenes (forests, crowds, etc).
• Massive instancing allows for memory efficient rendering of trees/crowds and other redundant scene elements.
• Shading is usually sharper because shading is performed at each sub-sample (and not per pixel as in REYES). Although it is possible to make REYES shaper by increasing the Shading Rate, it is usually not done (as it affects performance). Whereas the Path Tracer do not have options to reduce the shading rate.
• Scales better than REYES with increased number of cores.

Cons:

• Slower with displacements.
• Need more samples to render smooth motion blur and depth of field. This happens because it is actually more precise than REYES and there is more detail in the motion blurred effect, but this also induces more noise. And the sad part is:
• Increasing pixel samples (for aliasing and to reduce noise) has a direct impact on performance.