Newbie question - light frames are becoming green when uploaded

What camera do you use and did you use any filter? I can look at the data, just upload 10 light frames and your master calibration files for me to check out.

Go to https://upload.astropixelprocessor.com and use upload1 (or upload2 till 5) as username and password will then be the same as the username.

Create a directory named “daraobriain-greencast” and upload in there. Thank you!

@vincent-mod That's really kind of you. I've uploaded the Raw files (there's only 6 of them) and the result I got from the stacking process. I don't think I have a master calibration file (is the dark flats etc? I haven't done them yet, just starting out).

These were taken with a Sony a6000 with no filter. you can probably see the green hue on the result though.

Thanks again!

Thank you, I'll have a look by tomorrow (if the current storm here doesn't damage our internet connection 🙂 ).

So did you any chance to work out why my light frames were coming out green?

this green tint has happened with other shots I have taken as well, despite them appearing normal in Siri, Lynkeos and other programs...

I did! Woops, forgot to actually answer you. 🙁

So it seems the raw data simply has more green in the signal. If I don't stretch and just show the raw data in the histogram, you can see the green channel having its peak most to the right. Also, you should expose for longer as most of the signal is in the noise part of the histogram.

With star color calibration, you can get back to a more normal calibration of the colors, having not a lot of color in the data is likely because you should expose longer and have more data.

Do you use flats?

Cheers, Vincent

@vincent-mod

Thanks for getting back to me! It's hugely appreciated.

That isn't the histogram I'm getting at all though!

If, for example, I look at this picture in Apple photo, of the Hercules cluster

This is how it appears in other software as well.

But in APP when I upload it (RGB channel) it appears like this:

 And when I stack, it's impossible to get the colour back.

So what am I doing wrong?

Thank you!

Ok so let's take this step by step to be able to compare the proper things;

At first APP is showing the stretched image in the preview, with this histogram;

Turning the stretching off (deselecting DDP), reveals the data as-is with this histogram;

Now, you can see the histogram is in logarithmic mode, deselecting that checkbox reveals the linear data as-is;

That shows you that the data is very much to the left, meaning a large part of the sensor's ability to record data is not used. Normally you'd want to try and get the signal away from the left at least (say to 5-10% of the range), so that when stretching, the signal is free from the noise background as much as possible.

The other programs probably do some processing to the image already, like stretching and normalizing the image. In my last example APP doesn't, it shows you what you have. You can select normalization on the right where APP will try to normalize the background and it will come closer to what Apple photo shows I think.

Here's the histogram with the DDP (stretch) on again, showing the linear histogram and with normalization on;

That looks more like what you show, so that's the processing the other programs already do and it's not always what you want in astrophotography. There you want to have complete control.

When I turn off normalization, the lineair and stretched histogram looks like this;

That's the data again as-is, but stretched. It shows the offset to green which is in the data. To correct for that you need normalization, star color correction etc and to get proper color, you need more data and to calibrate your data properly with bias, flats etc.

I had to change the star color calibration quite a bit. I think it is because ther are no calibrations done and the stars are out of focus, it might struggle a bit there. But with that and adding some saturation I can still get some color;

That's great Vincent, thank you so much for doing all that; it has really helped explain it. One quick question though... You say to the do the normalization, with a button on the right hand side -is that the "Neutralize BG" checkbox?

Yes, sorry that was what I selected. It's just a preview though, real normalization is done when processing and post-processing.