Options tab

Contains infrequently used render settings, including settings for memory and performance, framebuffer settings, and various overrides.

Memory and Performance

Tile Scheme: Select from the following ways for Turtle to distribute tiles over the image plane:

Hilbert: A way for Turtle to achieve maximum coherence, the fastest rendering time possible.
Left to Right: Render from left to right.
Concentric: Starts in the middle and renders outward in a spiral.
Random: A good way to get an early feel for the whole picture without rendering everything.

Tile Size: A smaller tile gives better ray tracing coherence but more inefficient shading. There is no 'best setting' for all scenes.
Use one thread per CPU: When on, Turtle automatically detects the number of available processors.
Rendering Threads: Manually set the number of rendering threads.
Use SSE: Turtle uses specialized vector instructions to speed up the rendering. The cost is higher memory usage. Turn off SSE/AltiVec if Turtle starts swapping memory.
Use Instancing: Enables use of instanced geometry, which saves memory. If disabled all instanced shapes will get a separate copy of the geometry, which might decrease render time, but increases memory usage.

Framebuffer

Premultiply Alpha

If this box is checked the alpha channel value is premultiplied into the color channel of the pixel.

Note: Disabling Premultiply Alpha gives poor results if used with environment maps and other non-constant camera backgrounds, but it can be convenient when compositing images in post.

Premultiply Threshold

This is the alpha threshold for pixels to be considered opaque enough to be 'unmultiplied' when using premultiply alpha.

Enable Input Gamma Correction

Turtle renders everything in linear intensity space (not gamma corrected). This means Turtle assumes that all colors selected as inputs on Maya shaders are treated as linear, the same applies to all file textures. The output image produced by Turtle is also in linear space. If this is not desired Gamma Correction can be automatically applied to the input colors and textures, and to the output image.

For example, if the file textures are in gamma 2.2 and the resulting image needs to be in gamma 2.0, setting input gamma to 2.2 transforms the input textures from 2.2 to 1.0 (linear space). Setting output gamma to 2.0 transforms the rendered image from gamma 1.0 (linear) to 2.0.

If some file textures are in linear space, input gamma correction can be individually disabled on the file texture nodes. HDRI file formats such as OpenEXR and Radiance HDR are always treated as linear.

Gamma correction, both input and output, applies to all render modes including Vertex Baking.

Gamma correction is designed to correct colors with intensities between 0.0 and 1.0 between different display devices. Maya lets you set color values with any possible brightness, but this leads to very unpredictable results as a relatively limited color value can still be boosted to huge values by the gamma correction. Try to keep colors limited, and use Intensity sliders where available, as scalar values are never gamma corrected. This ensures that the color you see on your monitor transfers correctly to linear color space, and still has the boost in intensity that you want.

Input Gamma Correction

Selects the gamma space that input colors are assumed to be in.

Note: HDRI images are always considered linear.

Output Correction

Select the type of correction to apply to output colors.

None: Writes the linear colors directly.
Gamma: Takes the linear colors to the gamma specified in Output Gamma Correction.
SRGB: Converts the colors to SRGB when showing them. This is similar, but not identical to gamma 2.2.

Output Gamma Correction: Only considered when Output Correction is set to Gamma. Selects the gamma space the rendered image is transformed to.
Dither Final Color: Turn on if you want images dithered during conversion from high dynamic range float to low dynamic range integer colors.

Overrides

Ignore Light Links: When on, Turtle ignores light links. Use this option if you find there are issues with light links, which can occur in scenes with a lot of geometry and lights when no light links are available.

Tangent Space

Flip for odd UV winding direction: Forces Turtle to mirror tangent and binormal when UV has odd winding direction.
Vertex Level Orthogonalization: Orthogonalize tangent space basis vectors (tangent, binormal and normal) at every vertex.
Vertex Level Normalization: Normalize tangent space basis vectors (tangent, binormal and normal) at every vertex.
Intersection Level Orthogonalization: Orthogonalize tangent space basis vectors (tangent, binormal and normal) at every intersection point.
Intersection Level Normalization: Normalize tangent space basis vectors (tangent, binormal and normal) at every intersection point.

Output Verbosity