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Samples per Pixel |
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Samples per Pixel |
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The number of samples per pixel (sometimes called super-sampling) helps control the rendered quality of an image. It's most often noticed as aliasing - the staircase like effect at the edge of an object.
Each pixel in an image has to display a single color to represent all the materials and objects that might lie in that pixel. If there's only one object covered by a pixel and it has a uniform smooth material, then it's easy to set a color by just tracing one ray into the pixel and sampling the material once. But if a the material has a fine texture to it, or the pixel covers an area containing fine modeled detail, then we need to trace a larger number of rays into the pixel (sample rays) to get a better idea of the range of colors. Once we know enough about the detail in the pixel, we can display the most appropriate color. The total number of samples to be sent into a pixel is controlled by minimum and maximum limits. Threshold values control exactly how many samples are sent into a pixel based on the contrast in color between one sample and its neighbor.
Sampling is a dynamic process in Shaderlight. Increasing the max sampling level or adjusting the thresholds will also cause Shaderlight to trace additional sample rays automatically, without re-starting the render from the beginning. If a MELT change alters the level of detail in a pixel, Shaderlight will identify this and trace additional rays where necessary.
| • | Min/Max – Controls the minimum and maximum number of sample rays traced per pixel. A max value of 1 limits Shaderlight to 1 sample per pixel. Increasing the max value will improve the quality of the image at the expense of memory use. The min values can be less than 1, for example, using a value of 1/9 means that samples are taken every ninth pixel (in a block of pixels 3x3). This is commonly known as sub-sampling. When an image has broad areas of flat color, there is little contrast between each pixel so using sub-sampling will speed up the render and consume less memory, without any loss of quality. |
| • | Thresholds – The threshold values control how extra samples are taken in the image. As Shaderlight renders the image, it examines the contrast in color (in separate red, green, blue and alpha channels) between each sample and its neighbor. If the contrast is greater than the threshold value, then more samples will be taken. The lower the threshold values, the more sensitive to contrast Shaderlight becomes and the more samples will be taken (up to the limit set by Max). |
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