Debayer creates purple background


New member
Jun 29, 2020
I am just now trying PixInsight trial. I have been doing astrophotography for a couple of years using a one-shot color camera (ZWO ASI 071). I have been using a different image processing software but decided to give PixInsight a try. I plan on reporting back to my astronomy club on my comparison.

I was able to go through an entire project yesterday starting with building bias master, dark master, flat master. The problem I encountered is an overall purple cast when I calibrate the lights, biases, darks, and flats and then Debayer the result. I always select RGGB during debayer since that is what my ZWO ASI 071 calls for. I expect to see an overall green cast. I have been using Warren Keller book and process tutorials from on-line sources.

I tried to calibrate the biases, darks, and lights and then debayer them. I did get the expected green cast.

It is only when I also add the flats to the calibration process that I get the purple cast.

I am doing something wrong? It almost looks like when I add the flats to the calibration process the reds and blues become prominent and I lose the greens.

Shouldn't I always see a green cast after debayer?

I am just starting using PixInsight and would appreciate some guidance.




Well-known member
Feb 1, 2014

What if you properly calibrated your data... and you were imaging under the moonlight (a blue sky) or using some crazy LP filter?
Wouldn't that affect the color bias you see after a full calibration?

I am not saying there isn't an issue... but it seems ambiguous based on your description.



PTeam Member
Nov 23, 2009
could be a fits reader direction problem too. if your images are written out in one order and PI is set to read them in the reverse order, RGGB is the wrong setting. but rather than changing the debayer pattern it might make sense to just try reversing the reader direction. you can either pass the hint "up-bottom" or "bottom-up" to ImageCalibration when calibrating the lights. i can't say which to try because i don't know what direction your reader is currently set to (under the format explorer, double-click FITS). either switch it there to the other one (and click OK), or just note what it is and pass the opposite hint to ImageCalibration to see if this might be the problem.



New member
Jun 29, 2020
I took the images with a ZWO ASI 071 color camera and no filter and no moonlight/blue sky. I also processed the image using the same darks/biases/flats using 'Images Plus' with no problems and no blue color shift. I must be doing something wrong when I calibrate and integrate the flats into a flats master.

When I calibrate the lights using the darks and biases I get the expected green cast. It is only when I add the bias master that the image turns blue.
Is there something that I can do to check the integrity of the flats master? What if I debayer the flats?



Apr 19, 2020
Did you apply the ScreenTransferFunction (STF) with linked RGB-channels (chain symbol in top left corner of STF)? My flat-calibrated lights are always blue with linked RGB-channels due to the low intensity of blue of my flatfield box and therefore I have to unlink the RGB-channels in STF until I color calibrate with PCC.

Here someone had the "issue" I described above: