sRAW and how it is implemented?

[509]

I come from an astronomical imaging background.  My astronomical CCD camera allows what they call binning.  That is, when I bin the CCD it increases the pixel size and the sensitivity.

I notice on the new Canon D50 that they have two sRAW setting which result in much smaller sRAW files.  Does anybody know if these sRAW setting are achieved by binning the CCD?  This would result in much greater sensitivity than the RAW setting.

Since I am interested in using my photography camera's for pretty pictures of the night sky I would be interested in knowing how they work.  The astronomical CCD camera's have certain parameters that have to be met to meet scientific standards.   

So the question is "Does anybody know how the sRAW settings are achieved?" and "Does using the sRAW setting result in greater sensitivity?"

Thanks for your answers in advance.  If anybody knows how or where to find the answer that would also be helpful.  It is amazing the disconnect between photography and astronomical applications of CCD camera's.  It is like they are two different worlds!!

[Bob Atkins]

As far as I know, Canon have never provided details on exactly how sRAW is implemented.

It's not likely to be direct hardware binning because the sensor is a Bayer matrix sensor and so direct 2x2 binning would average 2 green, 1 red and 1 blue pixel, which could lead to color issues. With a monochrome (B&W) sensor, direct 2x2 hardware binning has no such problems.

I've seen it suggested it's done by using 4x2 (software) sampling which lets you average 4 green, 2 red and 2 blue pixels into 2 green, 1 blue and 1 red

There has been much discussion on the web about sRAW and speculation that it could reduce the noise in an image, but I've yet to see any concrete examples showing that to be the case. It doesn't change effective sensitivity since you need the same exposure at the same ISO setting for sRAW as for RAW and JPEG.

The best guess is that it's done in software, not hardware, and so whatever it is could be emulated by the appropriate processing of the full sized RAW file.

[509]

Thanks....I found this on the web.  It was talking specifically to the 50D.  No attribution, but it sounds like it is a software emulation.  Then again, this is the first time I had seen pixel binning used as a term on a photography site.

* Pixel binning for high ISOs. A new technology enabled by the complexity and processing power of DIGIC IV where they can bin 2, 4 or 8 pixels together at the raw level and average out the noise between them. This is seen by Canon as a key technology in balancing very high resolution sensors (in the 50mp range) with low noise at very high ISOs. Right now they are not pushing this too much with the 50D so as to not create confusion in the market (they see more potential for the technology as sensors get larger and in the pro-market).


I still I will post the same question on some of the astronomical sites and see if anybody knows the correct answer.

Thanks for your help.  You have a great web site.