Color Calibrating problems with Canon 450D stacks

[andreasmax]

Hi dear PI fellows,

I have a problem color calibrating my stacked images in PI.
Shoot my pictures with "normal" DSLR lenses on an Astrotrac mount.
The cam is a Canon 450D, modified, and I have stacked with flats, darks and lights.
When I apply the Auto STF with linked RGB chanels I get a very green image.
I did Background Calibrating, DBE, ColorCalibrating to the image, but the result is always the same: green!
Therefore it is quite impossible to do a MaskedStrech on it. I could, but would have very huge problems to get the colors right in the nonlinear state.
I checked the settings of the Batch Preprocessing and they suppose to be good.
Using PI 01.08.03.1123 x64 @ Mac OS 10.8.5
Sorry, if this question was asked before, I didn´t find anything in here.
Do you geeks have any helpful tipps for me?

Cheers from Austria,
Andreas

Stacked Image with linked RGB chanels:


Same stacked Image w/o linked RGB chanels:

[pfile]

getting the thresholds right for BN and CC can be a little challenging. if you don't set them right, then nothing happens. in CC, you can turn on "output white  reference mask" and "output background reference mask" to see if in fact anything happened. also on the console you'll see what scaling factors BN computed; if they are all the same or all "1" then the background threshold to BN was wrong, and it did not change the image.

rob

[gvanhau]

Hello Andreas.

After applying DBE and background neutralization, your image should show almost similar output with linked or unlinked channels in STF.

I am afraid that there is a problem with the sample placement in DBE or may be in the steps applied after DBE and BN.

If you could load the calibrated master, we can take a look.

Geert

[pfile]

also - when doing DBE, if "normalize" is checked then the channel weights will be the same coming out as going in and you'll still see a color cast. but the default is that normalize is unchecked, and so if DBE was successful a side effect is that the background is mostly neutralized.

rob

[andreasmax]

@ gvanhau: you say it! I already did them in a correct way with no result.

@ pfile: I did not have used normalze in that case. I know from my other cam, a Nikon D800 unmodified, that there is a bit of green in the images. That seems normal to me and I can handle them also. But never saw a case like this.

Both of you: Thank you very much for our quick help.

I have made a crop from the original stacked image (original was about 150MB) to about 9 MB. Please do not mention the bad quality of the image (not in focus, not tracked very good). This is just a test image.
Here is the link:
https://www.dropbox.com/s/oijkbfp5ug3issk/450Dmod_crop_green.fit?dl=0

Thx,
Andreas

[Harry page]

Hi

This problem occurs sometimes when there is a lot of noise in one channel

watch the RGB video http://www.harrysastroshed.com/pixinsight/pixinsight%20video%20html/pixinsighthomenewbie.html

and look at the linear fit bit and all will be fine

Regards

Harry

[pfile]

hi - try these process icons. first do the BN, then the CC.

they will appear in the middle of workspace 3. the BN will only work properly on the crop you posted.

rob

edit: the attachment is the result after those two processes, plus STF with channels linked copied to HT and saved as jpeg. not perfect but you can take it from there.

[andreasmax]

@ pfile: I will try this out! thx

@ Harry: Missed this video, since I never had problems… Just made a split from RGB to the single channels, applied the LinearFit and recombined them to a perfect result.

Both of you helped me very much, thank you both for this!

Trying to learn and study and learn and study PI for about a year and still struggeling with the basics.
But as we can see, every PI session the results are getting better. Love this application.

Andreas

[gvanhau]

Hello

I also did a test, and came to this solution. apply the processing icons (first DBE and then CC).

Note The DBE still generates a green cast image, that is because there is no real gradient in your image, the green is all over the image.
The color calibration parameters white reference lower limit and the background reference upper limit are critical try to adjust them in your
 image near the background level readout.

Regards
Geert