Orange master in Pixinsight

[Grierson]

Having built a light box for taking Flats I find that when adding them to the PreProcessing script in Pixinsight together with Lights and Darks I find that the background of the resulting Master Binning Light is bright orange. Using this script previously without flats resulted in the master output file having a green background. I can clearly remove the background colour but I can not understand the change. The light source for box is a white electroluminescent panel. Having adjusted the camera exposure time the RGB traces in the histogram on the ASIAIR interface fall centrally. Any thoughts would be welcome to this novice Pixinsight user. Thanks - John

[michael8554]

I don't have PI so guessing here.

Is your camera Mono or OSC ?

Why were your results green beforehand, is that considered to be normal ?

Posting a jpeg of a Flat and a Light might help.

Michael 

 

[Grierson]

Thanks Michael, in this case the camera is a OSC. I believe that it can be expected that green output from the script can be considered 'normal' in certain circumstances and it certainly is in my case although it is currently beyond my capabilities to explain why this should be. I am still in the foothills of the learning curve but I believe that it revolves around the RGGB makeup of the signal from the chip. I not sure that posting images would help and I was crossing my fingers that vlaiv or other knowledgeable member might offer an explanation.  ?

[michael8554]

Yes, some input from the experts would be way better.

Michael 

[sloz1664]

I believe what you are experiencing is light pollution. It your bias, dark & flat frames are removing the noise & dust bunnies. And as you state either ABE or DBE will rid you of your LP. It can be varying colours dependant on what time of the day or subject you are imaging. I've had green, brown, red & light blue calibrated masters prior to ABE / DBE.

Steve

[Grierson]

Thanks Steve, I'm not sure. I've had a different response from a member of the PI forum which I need to give some thought to as well. - John

[sloz1664]

What was the response from the PI forum, if I may ask?

Steve

[wimvb]

I wouldn't overanalyse the issue. It doesn't take much to throw colour balance off in a linear stacked image. Even if the rgb histograms seem very close, the math involved in image calibration can be sensitive to slight colour differences. As long as you can remove the effect with background neutralisation and colour calibration, you're fine.

[Grierson]

2 hours ago, sloz1664 said:

What was the response from the PI forum, if I may ask?

Steve

Steve this was Niall Saunders response which is not a million miles away from that of Win above. (Thanks Win) 

You are not doing anything 'wrong' as such. Perhaps you could adjust your exposure times slightly higher - but it wouldn's make a huge difference.

Fundamentally, your EL panel is NOT producing 'white' light, at least not as far as your imager is concerned. But that alone, isn't really too much of an issue either. It would seem to be 'white enough' to do the job.

And the 'orange cast'? I always used Background Color Correction to get the 'neutral grey' that I wanted from my Master Image (after Crop and DBE, and before Color Calibration).

After that, it was a long way diwn my list of noise removal and range compression steps before I ever considered trying to enhance the colours that I knew would still be lurking somewhere in the depths of my image.

However, if you just want a rought idea of what your image contains, then just remember to unlink the sliders in the STF window before applying an STF to your image.
 

[wimvb]

Some time ago I used a gray-blue door as a flat background. It worked, I never had any trouble creating a neutral background But I wouldn't recommend this. If the colour of a flat source is too far from neutral, this can lead to problems, especially if you use an OSC camera.

[Grierson]

Thanks again Wim. (Apologies for the earlier spelling error)

[wimvb]

23 minutes ago, Grierson said:

Thanks again Wim. (Apologies for the earlier spelling error)

No worries, glad to be of help.

[martin_h]

Ive had Green and Orange masters in the past, all from the same light source, DBE always sorts it out.

[Grierson]

22 hours ago, martin_h said:

Ive had Green and Orange masters in the past, all from the same light source, DBE always sorts it out.

Yes, I find the same but although I’m not a perfectionist I worry about how the cast affects the final image!

[wimvb]

38 minutes ago, Grierson said:

Yes, I find the same but although I’m not a perfectionist I worry about how the cast affects the final image!

Not at all.

Most of us image through light pollution, which can give an orange/yellow colour cast. If you live up north and have a really dark sky, then skyglow may be your "light pollution". I've even observed through very thin aurora (invisible to the unaided eye). This would give a strong green cast on any image. In the end your colour calibration routines will take care of this. What's left afterwards is noise, which may be stronger in one channel than in another, depending on which type of light pollution you have.