From: "mihalco" <mihalco@yahoo.com>

Date: January 21, 2010 3:34:12 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: New AstroIIDC user

Hi Milton,

I submitted a tech request to see exactly how binning is done on the Scorpion 20SOM.  I did come across the following article in their knowledge base:

http://www.ptgrey.com/support/\

kb/index.asp?a=4&q=163&ST=binning

Clipped from the article above:

+++++++++++++++++++++++++++++++

Pixel Binning

Pixel binning involves taking groups of pixels and combining them into a single pixel in some way. Point Grey implements the following types of  binning:

•Standard binning: This technique takes place directly on the sensor, before analog-to-digital conversion. Standard binning adds the analog charges from two or more pixels, then averages them, before formulating a single pixel value. 

•Subsampling: This technique is similar to standard binning, except the process takes place after analog-to-digital conversion, on the FPGA chip of the camera. In this case, the digital values of two or more pixels are added, then averaged, to formulate a single pixel value.

•Decimation: This technique is less commonly used on Point Grey cameras. It involves combining pixels simply by discarding a subset of pixel values.

Most Point Grey binning modes implement some combination of 2x horizontal and 2x vertical (2x2) binning and/or subsampling, resulting in a resolution that is both half the original number of pixels in height, and half the number in width. This decreased resolution usually results in a frame rate increase. However, because of the averaging of values that is performed after combining pixels, binning does not usually result in a significant increase in image intensity.  

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From reading this, my guess is that they clock two rows into the output shift register (standard binning), and then digitize each pixel in the output register and return an average for each 2 pixels (subsampling).  If this is the case, then all the photons are being collected (no rows or pixels discarded).  Good news, however, reporting the average rather than the sum of 2 pixels does drop 1 bit of resolution on the dim stuff (unless they leave it around as the 13th bit).  I'll report back what I hear from their tech support.

Regards,

Kurt

--- In Astro_IIDC@yahoogroups.com, Milton Aupperle <milton@...> wrote:

Hi Kurt;

From reading the spec sheet for the Scorpions 1600x1200  CCD, they  

are likely summing 2 pixels on the horizontal lines and then skipping  

each second line.

So that would explain how they get 2x the brightness and why they only  

get about 2x the frame rate.

<snip>