Here’s an interesting technique we discovered that allows you to render even faster using iray:
Sometimes it’s quicker to render a scene with less samples but twice its intended output size and resize the resulting render to 50% in post.
Let’s call it „Manual Oversampling“Here’s a rendering of a 50mm lens assembly. Original Resolution is 1280x720px. Render time was set to 15:00mins.
And here’s an enlarged detail:
And here’s the same scene rendered in 2560x1440px. Render time was set to 05:00mins. After rendering I just resized the image to 50% of it’s size, thus emulating what two times anti-aliasing would do and creating a 1280x720px image:
And here’s an enlarged detail of that resulting image:
Comparing both images reveals some interesting things:
Interestingly while the 15min version shows a little more detail in some areas (brighter reflections & caustics) it also exhibits more noise. For this specific scene these minor details don’t justify a rendertime three times as long as the resized 2560x2440px version. So for this scene i just went with rendering out bigger images and resizing them in post.
Tests with other scenes show that in most cases (yet depending on each scene individually) you can decrease your render times by 50% – 700% when using this technique. Iray just got even faster!Here’s another example. Rendering this city scene using manual oversampling I was able to render it almost seven times faster than rendering straight in the final resolution:
Oh – and the image on top shows the lens assembly after color correction and comping.