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Does any of their rendering techniques involve rendering an area at a higher resolution just to scale it down in order to mitigate artifacts? I know they use ray methods rather than rasterization however ray methods still have artifacts even when done with a ton of rays.. right?

I noticed a few moments in the film Moana that seemed to be poorly rendered because small details seemed fuzzy and sorta pixelated. Especially around the edges of a figure that was in focus with a slightly blurred background. Could they have used supersampling on those scenes to decrease the issue?

Dan Hulme
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J.Doe
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    The fuzzy look could come from the denoiser that they use. Renderman, the renderer that Pixar and probably Disney uses, has gotten a denoiser a while back. It has been used in Finding Dory, and could be used in Moana if they used Renderman to render it. – bram0101 Jan 04 '17 at 10:38
  • My favorite source that describes what Dan says below is found [here](https://renderman.pixar.com/view/basic-computer-graphics-2) incidenttaly its a pixar publication (document is a bit old but is still valid for the theory). @bram0101 why wouldn't Disney use their own renderer... Disney owns Pixar remember. – joojaa Jan 04 '17 at 10:57
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    Does anyone know what data compression scheme/format the cinematic releases use? Could it potentially be an artefact of skimping on the bit rate? – Simon F Jan 04 '17 at 11:21
  • Disney has also developed their own renderer, https://www.disneyanimation.com/technology/innovations/hyperion @joojaa – bram0101 Jan 04 '17 at 14:06

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Super-sampling for ray-tracing doesn't just mean rendering an area at higher resolution and then downscaling the finished image: in fact, this simplest super-sampling technique is really not effective enough for high-quality production rendering.

In a production ray-tracer, super-sampling means sending more than one primary ray per pixel (16 primary rays per pixel is a good average) and then using signal reconstruction techniques (i.e. not just averaging) to compute a colour for each pixel of the image. Using lots of primary rays doesn't just help to avoid aliasing (jaggies) from when polygons partially cover pixels; it also helps to smooth over noise added in shading, such as when sampling global illumination or fuzzy reflections.

In addition, super-sampling by sending more rays lets you jitter the sample positions to avoid the artefacts you get from regular sampling. It also lets you use the results of previously traced primary rays to decide where to put more samples.

For example, the simplest adaptive sampling algorithm is contrast based: within each pixel, you measure the contrast among all of the primary rays. Pick the pixel(s) with the highest contrast, and shoot more primary rays in those pixels. You can also use the contrast between samples to choose where in the pixel to shoot new primary rays, but then you have to use a more complex reconstruction algorithm to avoid bias in your result.

If you can find a frame-grab of the particular details you noticed, it would be possible to go discuss those in more detail. It's entirely possible that some artefacts are caused by a particular technique, and aren't related to super-sampling at all.

Dan Hulme
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  • Also, they don't send primary rays out in a regular grid pattern (which is effectively what you get by increasing resolution). – Nicol Bolas Jan 05 '17 at 00:47
  • I wonder if there are adaptive AA techniques which decide the successive sample positions based on previous samples rendered for the pixel – JarkkoL Jan 05 '17 at 01:25
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    @JarkkoL Yes, that's the usual way of doing it. The cost of the adaptive sampler is much less than the cost of additional primary rays, and it lets you get better results with fewer rays. – Dan Hulme Jan 05 '17 at 10:20
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    @NicolBolas That's a good point, so I've added it (and JarkkoL's clarification) to the answer. – Dan Hulme Jan 05 '17 at 10:26