Sampling Quality Rollout (mental ray Renderer)
 
 
 
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Render Setup dialog Renderer panel Sampling Quality rollout

Note: The Sampling Quality rollout appears only when the mental ray renderer is the currently active renderer.

The controls on this rollout affect how the mental ray renderer performs sampling for antialiasing rendered images.

Procedures

To use low sampling for previews:

To use high sampling for final renderings:

To view the sampling pattern:

Interface

Samples per Pixel group

Set the minimum and maximum sample rates for antialiasing the rendered output.

NotePresets for several sample rate combinations are available on the Rendered Frame Window as the Image Precision (Antialiasing) slider.
Minimum

Sets the minimum sample rate. The value represents the number of samples per pixel. A value greater than or equal to 1 indicates that one or more samples are computed per pixel. A fractional value indicates that one sample is computed for every N pixels (for example, 1/4 computes a minimum of one sample for every four pixels). Default=1/4.

Maximum

Sets the maximum sample rate. If neighboring samples find a difference in contrast that exceeds the contrast limit, the area containing the contrast is subdivided to the depth specified by Maximum. Default=4.

The values of the Minimum and Maximum lists are "locked" together so that the value of Minimum can't exceed the value of Maximum.

Filter group

Filter type

Determines how multiple samples are combined into a single pixel value. Can be set to Box, Gauss, Triangle, Mitchell, or Lanczos. Default=Box.

TipFor most scenes the Mitchell filter gives the best results.
  • Box filter: Sums all samples in the filter area with equal weight. This is the quickest sampling method.
  • Gauss filter: Weights the samples using a Gauss (bell) curve centered on the pixel.
  • Triangle filter: Weights the samples using a pyramid centered on the pixel.
  • Mitchell filter: Weights the samples using a curve (steeper than Gauss) centered on the pixel.
  • Lanczos filter: Weights the samples using a curve (steeper than Gauss) centered on the pixel, diminishing the effect of samples at the edge of the filter area.
Width and Height

Specify the size of the filtered area. Increasing the value of Width and Height can soften the image, however it will increase rendering time.

Default=Depends on the Filter type you choose:

  • Box filter: Width=1.0, Height=1.0
  • Gauss filter: Width=3.0, Height=3.0
  • Triangle filter: Width=2.0, Height=2.0
  • Mitchell filter: Width=4.0, Height=4.0
  • Lanczos filter: Width=4.0, Height=4.0

Spatial Contrast group

This control sets the contrast value used as thresholds to control sampling. Spatial contrast applies to each still image.

If neighboring samples in a frame differ by more than this color, the mental ray renderer does recursive supersampling (that is, more than one sample per pixel), up to the depth specified by the Maximum samples per pixel value. Increasing the Spatial Contrast values decreases the amount of sampling done, and can speed the rendering of a scene at the cost of image quality.

  • R, G, BSpecify the threshold values for the red, green, and blue components of samples. These values are normalized, and range from 0.0 to 1.0, where 0.0 indicates the color component is fully unsaturated (black, or 0 in eight-bit encoding) and 1.0 indicates the color component is fully saturated (white, or 255 in eight-bit encoding). Default=(0.05, 0.05, 0.05).
  • ASpecifies the threshold value for the alpha component of samples. This value is normalized, and ranges from 0.0 (fully transparent, or 0 in eight-bit encoding) to 1.0 (fully opaque, or 255 in eight-bit encoding). Default=0.05.
  • [color swatch]Click to display a Color Selector to let you specify the R, G, and B threshold values interactively.

Options group

Lock Samples

When on, the mental ray renderer uses the same sampling pattern for every frame of an animation. When off, the mental ray renderer introduces a quasi-random (Monte Carlo) variation in the sample pattern from frame to frame. Default=on.

Varying the sample pattern reduces rendering artifacts in animations.

Jitter

Introduces a variation into sample locations; see Sampling. Turning on Jitter can help reduce aliasing. Default=on.

Bucket Width

Determines the size of each bucket in pixels. Range=4 to 512 pixels. Default=48 pixels.

To render the scene, the mental ray renderer subdivides the image into rectangular sections, or “buckets.” Using a smaller bucket size causes more image updates to be generated during rendering. Updating the image consumes a certain amount of CPU cycles. For scenes with little complexity, smaller buckets can increase the rendering time, while larger buckets can make things render faster. For more complex scenes, the reverse is true.

Bucket Order

Lets you specify the method by which mental ray chooses the next bucket. If you are using placeholders or distributed rendering, use the default Hilbert order. Otherwise, choose a method based on how you prefer to see the image appear as it renders in the Rendered Frame Window.

  • Hilbert (best)(The default.) The next bucket chosen is the one that will trigger the fewest data transfers.
    TipAlways use Hilbert order when you use placeholders (see the Translator Options rollout) or distributed rendering (see the Distributed Bucket Rendering rollout).
  • SpiralThe buckets begin at the center of the image, and spiral outward.
  • Left to rightBuckets are rendered in columns, from bottom to top, left to right.
  • Right to leftBuckets are rendered in columns, from bottom to top, right to left.
  • Top-downBuckets are rendered in rows, from right to left, top to bottom.
  • Bottom-upBuckets are rendered in rows, from right to left, bottom to top.
Frame Buffer Type

Lets you choose the bit depth of the output frame buffer:

  • Integer (16 bits per channel)Outputs 16 bits per channel of color information.
  • Floating-Point (32 bits per channel)Outputs 32 bits per channel of color information. This method supports high-dynamic-range imagery (HDRI). This is the default output format.
    ImportantFloating-poing, 32-bit output is requred for lighting analysis.
    NoteWhen you render an image with floating-point, 32-bit output, you might see jagged edges in bright areas such as self-illuminated objects or reflections of light sources. The reason is that in floating-point rendering, the brightness of a pixel can be greater than 1 (“whiter than white,” so to speak).

    Above: In a 16-bit rendering, bright highlights are muted.

    Below: In a 32-bit rendering, bright highlights (on the lamp chains and the mirror), are strong and jagged.

    For example, suppose a pixel is sampled four times, and an object occludes the pixel one of those times. In a 16-bit rendering, this results in a 25 percent grayscale value for the pixel. The same thing happens in a 32-bit rendering, unless the object is bright. In that case, the pixel might be 20 times brighter than its surroundings, so the result does not blend into its surroundings, and the rendered highlight appears to be jagged or “aliased.” While this effect is apparent in the 3ds Max Design Rendered Frame Window, it is only apparent: if you use the image in a compositing program that handles HDRI images, for example, or open it and adjust its levels in an image-processing program such as Photoshop, the image appearance will be correct.