calibration question

[sharkmelley]

Mark,

There is indeed subtraction going on with Bernd's method 2 and in the final count the light is 1200 counts less than the raw image, but all of the hot pixels are still in the processed image.

Normal? Should I then run cosmetic correction to eliminate these hot pixels?

So you are using Bernd's method 2.  I use this all the time and it works well for me.

What dark scaling factor is being used? You can find it in the log file just after it writes the calibrated file:

[2017-09-17 21:11:40] Writing output file: D:/Processing/NGC7822/calibrated/light/DSC05636_c.xisf
[2017-09-17 21:11:40] Dark scaling factors:
[2017-09-17 21:11:40] k0 = 0.408
[2017-09-17 21:11:40] Writing image: w=4256 h=2848 n=1 Gray Float32

Mark

[tloebl]

I have tried both method 1 and 2. 1 works fine with no hot pixels remaining.  Here is the end of the log file with method 2:

2017-11-11_ngc151_Light_Lum_120sec_0001_-20C_c.xisf
Dark scaling factors:
k0 = 0.151
Gaussian noise estimates:
s0 = 8.925e-04, n0 = 0.697 (MRS)
Writing image: w=765 h=510 n=1 Gray Float32
53 FITS keyword(s) embedded.

This is method 1 log:

2017-11-11_ngc151_Light_Lum_120sec_0001_-20C_c.xisf
Gaussian noise estimates:
s0 = 8.847e-04, n0 = 0.738 (MRS)
Writing image: w=765 h=510 n=1 Gray Float32
49 FITS keyword(s) embedded.

[sharkmelley]

Interesting.  It does seem to show that dark optimisation is not working very well for your data.

Using method 1 you are implicitly using a scale factor k0=1 with a resulting noise level n0 = 0.738 (MRS)

Using method 2 the dark optimisation give a scale factor k0 = 0.151 with a resulting noise level n0 = 0.697 (MRS)

So the dark optimisation has reduced the noise level it is measuring but doesn't do a good job of hot pixel removal.

Mark

[tloebl]

These numbers are with the optimization threshold set to zero. I did notice that if I move the threshold up it result in eliminating some hot pixels. How is the threshold normally adjusted?

[sharkmelley]

These numbers are with the optimization threshold set to zero. I did notice that if I move the threshold up it result in eliminating some hot pixels. How is the threshold normally adjusted?

I've always used the default of 3.0 standard deviations.

Mark

[tloebl]

Thanks Mark,

looks like all hot and cold pixels clear up using cosmetic correction with 3 sigma. The result is similar numbers using noise evaluation script with method 1 and method 2.

Also appreciate Bernd's input on this subject.

[bulrichl]

Hi,

looks like all hot and cold pixels clear up using cosmetic correction with 3 sigma. The result is similar numbers using noise evaluation script with method 1 and method 2.

Yes, my results are similar. Please also take a look at the thread on optimization threshold:

https://pixinsight.com/forum/index.php?topic=11922.0

Bernd