I got the impression he approached it from visual pleasantness point of view. Which is more than perfectly valid when generating images for people to look at. In that business, if it's fast to compute and looks visually good to human eyes, it is perfectly acceptable to do a slightly "wrong" thing from signal processing point of view. At least until we have infinite computing resources.
I didn't read the source code, but judging by the article and images, he did appear to understand signal processing and sampling theorem. He appeared to look for a better sampler for a scan-line (think Pixar Renderman) or ray-tracer renderer (think POV-Ray).
My take is to have per pixel adaptive sample count as a function of standard deviation in certain sample radius larger than a pixel. Oversimplified, the higher the deviation, the more samples should be taken until the contribution is below some adjustable threshold. For example in a real ray-tracer you probably want to consider other variables as well, such as computational cost per sample. Ultimately the problem in visual renderers is how to get the best visual quality for computing resources available.
> Looks like he made the classic log/linear error too.
I can't see any telltale sign of doing linear processing for log space data in the images themselves. They all look correct. Retina / high-dpi display? Make sure your web browser is not resampling the images linearly in log space! Or worse, your monitor or graphics adapter, in case you're using a non-native resolution.
That's not very constructive. Can you point where he did that? For reference, source code is here: https://gist.github.com/Reedbeta/893b63390160e33ddb3c.
> without understanding basic signal processing.
I got the impression he approached it from visual pleasantness point of view. Which is more than perfectly valid when generating images for people to look at. In that business, if it's fast to compute and looks visually good to human eyes, it is perfectly acceptable to do a slightly "wrong" thing from signal processing point of view. At least until we have infinite computing resources.
I didn't read the source code, but judging by the article and images, he did appear to understand signal processing and sampling theorem. He appeared to look for a better sampler for a scan-line (think Pixar Renderman) or ray-tracer renderer (think POV-Ray).
My take is to have per pixel adaptive sample count as a function of standard deviation in certain sample radius larger than a pixel. Oversimplified, the higher the deviation, the more samples should be taken until the contribution is below some adjustable threshold. For example in a real ray-tracer you probably want to consider other variables as well, such as computational cost per sample. Ultimately the problem in visual renderers is how to get the best visual quality for computing resources available.
> Looks like he made the classic log/linear error too.
I can't see any telltale sign of doing linear processing for log space data in the images themselves. They all look correct. Retina / high-dpi display? Make sure your web browser is not resampling the images linearly in log space! Or worse, your monitor or graphics adapter, in case you're using a non-native resolution.