What is "Zero or insignificant signal detected: Empty image?

[TrickyDicky]

What is "Zero or insignificant signal detected: Empty image?
While trying to integrate 4 jpg images the above pop-up comes as an error. Bug, or what?
Images are not empty, and they are of not insignificant signal, just normally stretched jpegs ..
 

[Nocturnal]

Hi,

I would not expect that error but it may well have saved you a lot of trouble. You really should not try to stack jpg images. Stacking works because it assumes each pixel that gets averaged is a value from the same probability distribution. When you average a number of these pixels the resulting value has less uncertainty or noise.

As you know Jpgs are converted in camera using a proprietary algorithm. The algorithm adjusts various parameters depending on image content. This means that pixels of the same object (say a galaxy) are not from the same probability distribution. Averaging doesn't mean anything. Your resulting image may be worse than the best of the set.

If you have the chance please try taking RAW shots with your camera next time. They are linear and can be combined. Tell us a bit more about your setup if you like.

[TrickyDicky]

Thanks Sander,
I saved the images as FITs and the same occurred. Then I isolated the image that caused this error, so it was only one "funny" frame.
Visually it was not different from the others, but PI decided to produce an error. The frame's signal doesn't look "insignificant" or "zero", so what does that error actually mean?
#TD

[Nocturnal]

Hi TD,

changing the format does not do anything to the underlying data, sorry. I still recommend using RAW or FITS straight from your camera for stacking.

Glad the issue is limited to a single image. I don't know what the error means. Hopefully someone with more knowledge of PI internals will be able to help.

[georg.viehoever]

Hi TD,
maybe you upload the difficult image somewhere (plus one of those that dont cause problems), so the experts can have a look.
Georg