There is a sneaky render setting in Blender that can increase your render time by 128x (or more) with a single click. It's called "Square Samples" and if you're not familiar with what this setting is doing, you might be in for a bad time!
The default number of Cycles samples is 128. Turning on "Square Samples" will take that number, and square it (mathematics), making it 16,384!
We've had dozens of users over the years that were not aware of this. They received some spectacular price quotes when submitting their projects with us. Hundreds of times higher than expected. Why? Because they checked "square samples".
So, why was this setting added to Blender? The description claims that squaring the samples makes for "easier artist control". Why is this?
Easier artist control
The more Cycles samples you use, the better the image you get (less grain/noise), but it also adds render time. So this is a bit of an optimisation problem. You have to figure out how many samples gives a clean image, and still has an acceptable render time (and/or price).
At low values, the number of Cycles samples has a huge influence on the final image quality. The difference between 16 or 32 samples is massive:
16 Samples
32 Samples
As you go to higher sample values though, the law of diminishing returns will kick in. Adding samples will seem to only increase render time, but not affect image quality as much. The difference between 100 and 116 samples is almost not noticeable:
100 Samples
116 Samples
This is where squaring your samples can help.
With your samples value squared, the law of diminishing returns is less extreme. Now, the sample count does not grow linear, but parabolic, sort of counteracting it. When you increase by 1 at low values (from 10 to 11) it will jump 21 "real" samples (from 100 to 121). But when you increase by 1 at higher values, the "real" increase is also higher. (100 to 101 adds 201 "real" samples, going from 10,000 to 10,201).
Should Blender even have this setting?
Whether this makes the squared samples setting worth adding to Blender is up for debate. I would argue it adds unnecessary confusion, especially for beginner users.
But, if you do want to use it, keep your sample values low. I recommend a range of about 4 - 50, which will actually map to a range of 16 - 2500 "real" samples.
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