Disney's Practical Guide to Path Tracing

Here's a kind of silly but accurate view of path tracing for animated features [this video] Typically, most pathtracers use a technique called Monte Carlo Estimation, which means that they continuously loop over every pixel in an image, and average together the incoming light from randomly traced light paths. To calculate motion blur, they typically sample the scene at least twice (once at camera shutter open, and again at shutter close). Adaptive sampling rendering techniques will typically converge faster when there is less motion blur. One of the biggest time-saving techniques lately, is machine learning powered image denoising [1]. This allows the renderer to compute significantly fewer samples, but then have a 2D post-process run over the image and guess what the image might look like if it had been rendered with higher samples. Animated movies and VFX render each frame in terms of minutes and hours, while games need to render in milliseconds. Many of the techniques used in game rendering are approximations of physically based light transport, that look "good enough". But modern animated films and VFX are much closer to simulating reality with true bounced lighting and reflections. [1] [link]