[PKay (Peter)]

To continue with analysis of the ASI1600 working toward ideal GAIN and Sub length.
Once again this is only my take on things (I have to start somewhere).
This is not definitive information.
Please correct me if I am still wrong.

Once again using Shiraz’s formula as a starting point.
Target_ADU = BIAS + 10*RN*RN/GAIN is for a CMOS camera such as the ASI1600MM.
Ray says that the Background ADU count should be slightly higher than the Target_ADU

It is easy enough to calculate the Target ADU from the camera specifications.
In my case (previous post) it works out to be 51 ADU at unity gain.

So then, I have to analyse one of my LIGHT images to see just what is happening.
For example what is the average background ADU (K) value?
The ASI1600 uses a 12BIT ADC.
I posed a question to ZWO about this and the response was:
‘The ADC is 12bit but software save the 12bit data in the high 12bit of 16bit format’.

In Sharpcap I can select RAW16 saved in a .fits file.
This results in an image of 31.264 M bytes.

When I take an image, the ASI1600 represents each pixel with a value from 0 to 4096 (12 bits).
The BIAS is included in this (from 1 to 50), so insignificant.
Sharpcap then takes this number and writes it into a 16bit format.
As said above, this is in the high end of the 16bits (this is like multiplying the number by 4).

But how does this effect the operation of the Statistics tool in Pixinsight?
After a simple test on BIAS images (see previous post), the numbers match precisely when I choose a 12bit ADC in the tool.
I can only guess, but the Statistics tool must ignore the low 4 bits in this case ie: interpret the 16bit number as a 12 bit number.

In summary, for me to get the correct ADU value for analysing images, I have to select 12bit in the tool.
This will show ‘Full Well’ at 4095.
This ADU (K) value should correlate with the target_ADU value of 51 calculated earlier.

Also, I think I have worked out there is no need to Debayer the image or stretch it, to use the STATS tool, in other words evaluate the RAW . fits file.

Help appreciated.