Image

Image Block

There image block dictates the resolution of the image as well as a few other image options. The samples and jitter lines are optional and if they are left out samples will equal 1, contrast will be 0.1, and jitter will be false will be used as the default.

image {
  resolution 800 600
  aa 0 2
  samples 4
  contrast 0.1
  filter gaussian
  jitter false
}

Anti-Aliasing

The aa line is the settings for the adaptive anti-aliasing. These control the under/over-sampling of the image. The image will be first sampled at the rate prescribed by minimum aa value (the first value). Then, based on color and surface normal differences, the image will be refined up to the rate prescribed by the maximum aa value (the second value).

• A value of 0 corresponds to 1 sample per pixel.
• A value of -1 corresponds to 1 sample every 2 pixels (1 per 2x2 block)
• A value of -2 corresponds to 1 sample every 4 pixels (1 per 4x4 block)
• A value of -3 corresponds to 1 sample every 8 pixels (1 per 8x8 block) ...
• A value of 1 corresponds to 4 samples per pixel (2x2 subpixel grid)
• A value of 2 corresponds to 16 samples per pixel (4x4 subpixel grid)
• A value of 3 corresponds to 64 samples per pixel (8x8 subpixel grid)

Examples:

- quick undersampled preview: -2 0
- preview with some edge refinement: 0 1
- final rendering: 1 2

You can turn adaptive anti-aliasing off by setting the min and max values to the same number. For example, an aa of 0 0 will be 1 sample per pixel with no subpixels.

Samples

Samples are the number of samples. When used they indirectly affect many aspects of the scene but directly affects DoF and camera/object motion blur.

Contrast Threshold

There is a line in the image block in which you can change the default contrast threshold. This affects the point at which the renderer decides to adaptively refine between four pixels when doing adaptive anti-aliasing. This line isn't required and the default is usually the right setting.

Filters

If you are oversampling the image (i.e., having the min and max aa positive numbers) you will likely want to use more advanced filters to control the look of the image. The available filters are:

box (filter size = 1)
triangle (filter size = 2)
gaussian (filter size = 3)
mitchell (filter size = 4)
catmull-rom (filter size = 4)
blackman-harris (filter size = 4)
sinc (filter size = 4)
lanczos (filter size = 4)
bspline (filter size = 4)

Check this page out for a good overview of filters. Triangle and box are better for previews since they are faster. The other filters are recommended for final image rendering.

• box

• triangle