Optimizing Caustics
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These render settings are high quality, but take more than four hours to cast photons on a dual proc Athlon 1900MP running Linux. |
[newline][newline]Optimizing Caustics is straightforward - the more photons the better. In the Render Options, locate the Photon tab and cast your gaze at the options there. First, make sure the effect is actually toggled on. Then optimize the settings. The best way to proceed with optimization is to get a stop watch, a pen and some paper, and make tests, trading time against quality.
[newline]The important values to modify in this scene were Accuracy and Radius. In scenes where not enough caustics are thrown, XSI can blur the results, sampling a bunch of photons given by the accuracy number, and blurring them together with the radius given by the radius value. In our case, we want sharp defined caustic patterns, so the accuracy is set low, to 50, and the radius is set low as well, to .25.
[newline]Now all that is left is to check the lights that cast photons and turn up the number of emitted caustics, while at the same time turning down the energy in each caustic so you don't blow out the lighting in your scene. I used 400,000 caustics per light with caustic intensity set to 1500.
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[newline]| Global Illumination, Final Gathering, and Caustics all increase render time |
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[newline][newline] [tab] In a good render, the rendering engine puts the most time where there is the finest detail. We can make sure this happens by using adaptive anti-aliasing with a small threshold. Setting the Min Aliasing to 0 and the Max Aliasing to 2 means that XSI will start with just one ray for each pixel, and then compare it to the neighboring sample ray that it cast previously. If the neighboring pixels are too different, then XSI will subdivide the space between them and cast a few more samples. Each of those will be checked against the neighboring samples in the same way, for two recursions or until the difference between neighbors is less than the threshold you set in the render options. The default threshold of .2 is too high. For a finer image with not much more render time you want a small threshold, like .05 for value in the HSV color system (or .05 for each of Red, Green and Blue if you are mired in the RGB system.)
[newline][newline]Choosing the Right Filter
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[newline]| the final rendered image has Final Gathering, Global Illumination and Caustics all working together to illuminate the scene |
[newline][newline]The filter blends the samples together to make the final pixel color value. The new Mitchell and Lancos filters are excellent - use them all the time unless you want a blurry image in which case box and Gaussian are good options. Set the Filtering Size X and Y to 5 by 5 for good results with very little additional time spent in the rendering process.
[newline][newline]Rendering out high bit depth images
[newline]Since you are rendering high dynamic range images, it seems like a good idea to render a higher bit depth image. If you render a tif, you can choose to save 16 bits per channel of color data for each pixel. The options for clipping and dithering determine how the additional color info in the render is discarded.
[newline]Finally, it's time to render. Start with a small file because you really don't know how long it will take to render. Then once you have a baseline time estimate, scale it up and render a bigger file.
[newline][newline]Happy lighting!
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