Hi,

I have started using PI for calibrating, aligning and stacking very recently. Instead of using the BPP, I'd like to use the dedicated tools to have a better control on the whole process. Thanks to the Noise Evaluation script, I was able to track the noise levels after each step. The following data belongs to Luminance images shot by Atik 460 EX Mono camera:

**Uncalibrated sub**

m106_1_600sec_1x1_L_frame30

Calculating noise standard deviation...

* Channel #0

**?K = 2.304e-03**, N = 157934 (77.90%), J = 4

**Calibrated sub - with Bias and Flat Masters**

m106_1_600sec_1x1_L_frame30_c

Calculating noise standard deviation...

* Channel #0

**?K = 2.297e-03**, N = 4647476 (76.88%), J = 4

**CosmeticCorrection applied sub**

m106_1_600sec_1x1_L_frame30_c_cc

Calculating noise standard deviation...

* Channel #0

**?K = 2.295e-03**, N = 4786605 (79.18%), J = 4

**StarAligned sub**

m106_1_600sec_1x1_L_frame30_c_cc_r

Calculating noise standard deviation...

* Channel #0

?K = 2.030e-03, N = 4484671 (74.19%), J = 4

**Stack of 30 frames**

integration

Calculating noise standard deviation...

* Channel #0

**?K = 4.611e-04**, N = 3256902 (53.88%), J = 4

So, I'm getting more than 2x more noise in the final stack.

On the other hand, the situation with flat frames is like the following:

**Uncalibrated flat sub**

m106_1_0_76sec_1x1_L_frame1

Calculating noise standard deviation...

* Channel #0

**?K = 5.214e-03**, N = 5910648 (97.78%), J = 4

**Calibrated Flat sub - with Bias Master**

m106_1_0_76sec_1x1_L_frame1_c

Calculating noise standard deviation...

* Channel #0

**?K = 5.214e-03**, N = 5910693 (97.78%), J = 4

**MasterFlat - Stack of 40 frames**

MasterFlat_L

Calculating noise standard deviation...

* Channel #0

**?K = 1.400e-03**, N = 5864821 (97.02%), J = 4

With the flats I'm getting almost 1/4th of the noise of the individual frames.

**The BiasMaster used in the calibration of these light and flat frames - Stack of 200 frames**

BiasMaster_1x1_0C_20130729_200x

Calculating noise standard deviation...

* Channel #0

**?K = 2.791e-05**, N = 5170396 (85.53%), J = 4

**The SuperBias produced from the above BiasMaster**

SuperBiasMaster_1x1_0C_20130729_200x

Calculating noise standard deviation...

* Channel #0

?K = 9.400e-06, N = 2611685 (43.20%), J = 4

**The subs at the beginning and end of the bias capture**

Target_Set_1_0_001sec_1x1__frame1

Calculating noise standard deviation...

* Channel #0

**?K = 3.089e-04**, N = 5915885 (97.86%), J = 4

Target_Set_1_0_001sec_1x1__frame200

Calculating noise standard deviation...

* Channel #0

**?K = 3.092e-04**, N = 5913929 (97.83%), J = 4

Can somebody please explain me what's going on here ? Also, why is the SuperBias more noisy ?

I've started reading the relevant chapter in The Handbook of Astronomical Image Processing but it will take some time to go through all the details there. I thought I could get some quicker response from the gurus here.

Many thanks

Sedat