How to predict/determine how many samples will be enough for a render?
Let´s say I have a 7000x4000 image and Direct Light Diffuse as a kernel. I´m ready to render a final image but I´m not sure how many samples I need to make a good looking picture. I assume 2000 samples will be sufficient. I spend 10 hours rendering the image just to find out that 2000 samples was not enough. Then I will have to render the picture again...
How should I find out the sufficient sample amount?
If I render a region, then the samples amount doesn´t correspond to the whole 7000x4000 image...
Can I up the samples amount during rendering, if I find out with zoom function that the samples amount wasn´t enough?
Thanks,