Required samples prediction?

[Builtdown]

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,

[juanjgon]

Perhaps for this workflow you could set a high number of samples at the beginning (10000 or more) and stop the rendering when it is noise free with the "abort+continue" button to get the image at this point.

Also if you have one image rendered, and you want to add more samples to it, you could render a new image and average the two rendered images in post (with Photoshop or other tool) to get a final image with all the samples and less noise.

-Juanjo

[gordonrobb]

Sounds interesting. Can you give some pointers as to how you would use two images in PS to make a better looking one? Just out of interest?

[Draydin_r]

All that you would have to do to average the two images would be to have the two images on separate layers (in photoshop) and reduce the opacity of the top most layer to 50%.