On Wed, 22 Nov 2006 00:54:21 GMT, "Terry B"
wrote:

Thank you Chris.
Another question.
When I image with the genesis version I have an offset of about ~3500 that I
have to subtract out. The SBIG camera seeme to have essentially on offset or
about 100 only. Is this just different electronics or does the SBIG software
remove the offset before displaying the image?

That's purely a function of the camera electronics or firmware. Cameras
normally have an offset or pedestal added to each pixel to ensure that
there are no negative values. The amount is pretty arbitrary. I'm
surprised that the Genesis uses such a high value, though. It's enough
to seriously bite into the available 16-bit output range, and far more
than should be necessary.

The pedestal shouldn't be removed by processing software from the raw
image. It will be removed automatically during dark subtraction, which
is usually a requirement of processing. For very low noise cameras that
may not require a dark frame, you would still use a bias frame (or
synthesized bias frame) to correct for the pedestal.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com