Blue Channel: Dark Scaling Factor is to low

[Claus]

Hello PI Users,

I hope anyone can help. I want to calibrate my RGB light frames with the image calibration tool. I fed the tool with a good masterbias, masterdark and a masterflat. The Dark Optimization Checkbox was ON. While watching the process I noticed different dark scaling factors:

Red Channel:     0,9-1,1
Green Channel: 0,9-1,1
Blue Channel:    0,3-0,5

The result is a bad calibrated blue channel with a lot of remaining hotpixels and so on.
Beforde you ask, yes darks and lights are the at the same temperature and duration. Factor 0,9-1,1 seems normal to me, but 0,3-0,5 seems to low.

I have looked at the raw images in the blue channel in more detail and found that the blue channel is generally much less noise than the red or green channel. Could this be the cause of the problem?

Should I forget the optimization checkbox, because darks and lights are at the same temps and duration?



Claus

[georg.viehoever]

What kind of camera are you using?

[Claus]

Hello Georg,

i am using ATIK 383L+ (mono with Baader Filters).

[Claus]

Update:

the dark scaling factor varies depending on the optimization window (px) with crazy values:
 


3500 (Complete Image):
R 0,9
G 0,8
B 0,3

2000:
R 0,75
G 0,76
B 0,31

1024px (Standard):
R 1,0
G 0,8
B 0,2

950:
R 0,95
G 0,72
B 0,17

900:
R 0,95
G 0,75
B 0,79


900px - 500px seems to be good value to use.

I have my images analyzed from the center to the borders, but all three channels look the same. I also use no dithering or similar.

[Juan Conejero]

Hi Claus,

I think you've found where the problem is. In this case, you should use the whole image for dark optimization. I haven't seen a similar problem before. Could you please upload one of these raw frames?

[Claus]

Hello Juan,

thank you taking care of my little problem. When I use the whole picture (Optimization Value = 0 or > 3500)
the result is always:

R 0,9
G 0,8
B 0,3 (too low)

I have uploaded the pictures here:

Red Channel:     http://www.astrofreunde-franken.de/dump/Red.fit
Green Channel:  http://www.astrofreunde-franken.de/dump/Green.fit
Blue Channel:    http://www.astrofreunde-franken.de/dump/Blue.fit
Masterdark:       http://www.astrofreunde-franken.de/dump/masterdark.fit

(right click, save target as  "name.fit")