Import images from a folder with a minimum grayscale intensity

[diebachs]

Hello,
I generate some thousands grayscale images (most of them without signal intensity) which I have to process in two steps:
1) sort out all images without signal / only background signal (e.g. every image with a maximum value of less than 20)
2) import "All Files in Folder" and sum up the intensity for the remaining images.

The second step I do with the "Z Projection" and it works fine, but due to the many images and 32bit operating system I cannot process with all images - with and without signal. Does anybody know how to delete "empty" images in a folder or leave these images out from being imported into a stack?

Thanks, Markus