CCD overscan

Sequence Generator
1

Please help - is there any way to produce an overscan with SGPro using an FLI camera (ML16803)? I can get an overscan when I work with maxim DL, but it appears to be impossible for me to call for an overscan with SG Pro. Thanks for help.

2

We do not currently support overscan. Is there a reason that overscan is needed? How would you use it?

Jared

3

Hi Jared,

I was reading about this just last week. So this post piqued my curiosity. Apparently with professional CCDs overscan correction is done routinely. Some of the amateur level CCDs don’t even have overscan.

Here’s an explanation of the correction which is similar to bias correction: https://users.astro.ufl.edu/~lee/ast325/handouts/ccd.pdf

This paper actully says how its done: https://arxiv.org/pdf/2008.12633.pdf
Quote: “The data is overscan corrected by subtracting from each pixel row the row-wise median values, read from the CCD overscan areas.”

Ajay

4

Hi Ajay,

All CMOS and almost all CCD amateur cameras are doing this in the hardware.

To test this, take a 10 sec dark frame and then a 1000 sec dark frame and substract a bias frame from both. Do all of this at room temperature, to increase the effect of the dark current. You would expect to have a 100 times higher average value for the second dark than for the first (due to the dark current) but they will be practically equal.

Kind regards,
Horia

5

Thanks Horia. Good to know and something to look into.

Ajay

6

It is easy to spot - the image has different dimensions / black border. I noticed that TSX includes the overscan whereas SGP excludes it ( QHY CMOS cameras).

7

I understand the overscan a little better now, having read on it. Pixinsight has ways to properly apply overscan corrections called trimming. I had always wondered about those settings. The links below have some resources for folks who have KAF8300 based chips:

Using PI: Overscan calibration to improve dark frame scaling (SBIG STF-8300M + PI) - IceInSpace
STF8300 discussion: STF-8300C Overscan and Trim Regions?! | Diffraction Limited Support Forum

If SGPro downloaded these extra pixels, I’d be curious to see if trimming makes any difference.

Ajay

8

Sorry for the delay in responding. We are doing studies of the low surface brightness Universe, and we use the overscan part to track the bias level within each frame, for more precise bias correction (we use the mean level to prescribe subtraction of the mean bias frame). Maxim DL for example does allow an overscan read for all CCD cameras supported, thank you.