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Old 05-07-2014, 03:58 PM
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Binning v pixel size

Not sure if this has been discussed before, but here goes.
Just want to test my line of thinking:
With larger pixel cameras, the sensitivity is increased with decreased resolution.
Smaller pixels ccd cameras with binning can achieve the same effect.
Therefore larger pixel count ccd with smaller pixel sizes with binning can achieve similar resolution as smaller pixel cameras with larger pixel sizes.
Hope that made sense.

Bo
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Old 05-07-2014, 05:27 PM
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More data required....
a 6 micron pixel, 2 x 2 will be the equivalent of the 12 micron pixel.
Comparing that to a "native" 12 micron pixel camera, would require knowledge of QE etc.
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Old 05-07-2014, 05:32 PM
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Yes, that is my experience. It does depend on the CCD as KAF8300 does not do a clean binning and there is some loss. But Sony ICX694 bins cleanly and 2x2 binning does seem to emulate a 9 micron pixel very well only cleaner and more sensitive.

Greg.
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Old 05-07-2014, 06:17 PM
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Clean binning ?

Hi Greg

You caught my attention with your comments re clean binning. Could you amplify a little? I am presuming there is some loss due to the architecture of the chip but is there any data on the size of the loss?
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Old 05-07-2014, 06:20 PM
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Clean binning ?

Hi Greg

You caught my attention with your comments re clean binning. Could you amplify a little? I am presuming there is some loss due to the architecture of the chip but is there any data on the size of the loss?
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Old 05-07-2014, 06:25 PM
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Larger native pixel sites on the chip have a larger well depth than small pixels. I dont think binning small pixels increases well depth.
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Old 05-07-2014, 07:16 PM
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well depth is 4x with 2x2 binning, but the transfer and output electronics usually cannot handle that much signal - I think that the makers generally turn down the gain by about 0.5 to protect the output stages, so that you get a compromise of up to about 2x the effective well depth - seems that it varies with the chip design. Still quite usable if the read noise is low - but sometimes the read noise also suffers with binning. Overall, binning is a useful extra facility, but not quite the same as a "real" larger pixel. As Greg points out, the icx694 comes pretty close though.

Software binning is possibly a better option overall - if you expose the 1x1 subs for long enough to bury the read noise you get all the advantages (and disadvantages) of bigger pixels - 4x the sensitivity, 4x the well depth and 1/2 the linear resolution.

Last edited by Shiraz; 05-07-2014 at 07:30 PM.
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Old 05-07-2014, 08:01 PM
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Ray,

If you don't mind, how is software binning done? I assume it's not all all the same as reducing the image size in Photoshop.

Thanks,

Peter
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Old 05-07-2014, 09:14 PM
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Hi Peter.

I use software binning in Nebulosity - presume that it is just averaging data from 4 pixels to get one new pixel (the pixel noise stats indicate that this is what it does). If the read noise is low enough, this is functionally the same as you would get from a perfect 2x2 binning process, only with signal and noise scaled by 0.25.

Reducing size could be done the same way - but it could also be done by just taking one out of the four pixels to represent the new pixel data, or using a surface fitting process - would need to know how Photoshop does it under the hood.

Last edited by Shiraz; 06-07-2014 at 02:41 PM.
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Old 05-07-2014, 09:42 PM
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Thanks for all the informed comments.
Crappy weather makes time for more education...
Bo
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Old 06-07-2014, 12:26 PM
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What I meant by clean binning is theoretically 2x2 binning should be 4X the signal to noise. On KAF8300 because of something to do with the horizontal registers, see here:

http://www.ccd.com/ccd103.html

What I have read is that with the KAF8300 chip there is some issue with the horizontal register such that it does not do a proper 4X addition of the 4 pixels that make up 2x2 binning. So it loses something in the process. You can this when you use a KAF8300 camera in that 2x2 binning gives a gain but not the 4X you might expect more like 2X.

On the other hand a chip that does 2x2 binning very well like the Sony ICX694 you do see pretty much a 4X improvement and with its small pixels it emulates a 9 micron pixelled Kodak chip quite well but with increased sensitivity and lower noise. The downside is its a small chip and has a narrow FOV which is useful for some shots (galaxies).

Ray I have only experimented briefly with software 2x2 binning and noticed it also reduces resolution noticeably. So no free lunch there.

Greg.
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Old 06-07-2014, 12:32 PM
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Greg,
I use 2 x2 binning when chasing faint spectra....
There's no loss of resolution as long as the binned pixel size still meets the Nyquist requirements.
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Old 06-07-2014, 02:28 PM
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Quote:
Originally Posted by Merlin66 View Post
Greg,
I use 2 x2 binning when chasing faint spectra....
There's no loss of resolution as long as the binned pixel size still meets the Nyquist requirements.
+1

the resolution loss with software binning is exactly the same as with hardware binning - 1/2 the linear resolution when you use 2x2 binning. The free lunch of software binning is that you get more dynamic range.

minor point Greg, but perfect binning gives you 4x the signal, but only 2x the SNR if you are shot noise limited (which is usually the case).

Last edited by Shiraz; 06-07-2014 at 02:43 PM.
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Old 06-07-2014, 07:58 PM
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8300 chip

Hi Greg

After your comment I fired off an e mail to QSI (I have a QSI 683). Their reply:

Ulrich,

Kodak doesn't publish full well capacity figures for the HSR and Output Register on the KAF-8300, but we have been able to determine effective values through Photon Transfer analysis. Well depth of the HSR is about 37,000 e-. Well depth of the OR is about 55,000e-. Low gain on the 683 is set to 1.1e-/ADU to maximize the dynamic range of the Output Register.

Take a look at this Knowledge Base article for a bit more detail about how this relates to Flats.

http://store.qsimaging.com/kb_results.asp?ID=28

Regards,
Kevin

Essentially while 2 X 2 binning is able to collect 100,00 photons only 55,000 can be read through the output register.

Ulrich
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Old 07-07-2014, 09:42 PM
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Thanks for that. That sounds about right.

Greg.
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Old 08-07-2014, 09:57 AM
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Ok, more questions,
I looked up Celestron Nightscape 8300 which uses the KAF 8300 sensor and here is what I lifted from their website

"Full Well Capacity 25,500 e-
Imaging Sensor Kodak KAF-8300 Color Sensor
Mounting 2" barrel and t-thread
Operating Environment 40C to -40C (104F to -40F)
Optical Window High transmission Schott B270 glass
Quantum Efficiency 33%@630 nm; 40%@550 nm; 33%@470 nm
Read Noise (RMS) 8 e-"

Am I missing something here
Bo
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Old 08-07-2014, 10:07 AM
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Is this a 16bit camera???
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Old 08-07-2014, 11:03 AM
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Yes, 16 bit A/D conversion.
Full specs on the website http://www.celestron.com/browse-shop...300-ccd-camera
Click on the specs and expand.
Bo
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Old 08-07-2014, 12:58 PM
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that's entirely consistent with earlier posts.

Binning occurs in 2 steps.

1. First, the signal from pairs of adjacent pixel is added by putting the charge from 2 pixels (rather than one) into each cell of the shift register - for a saturated 8300, this results in trying to stuff 51,000 electrons in each SR cell. But, the shift register cells cannot hold that much and saturate at 37,000 electrons - so you lose ~1/3 the available full charge in this step.
2. The (37,000 electron) charge packets in the SR cells are then transferred into the output register in pairs, so 74,000 electrons turn up at the output register for each binned pixel. The output register cannot handle more than 55,000 electrons, so some of the available electrons are again lost to saturation and you are again down by about 1/3.

ie, in the two processes, you lose about half of the total number of electrons available from the 4 saturated pixels - you start out with 25,500x4 and end up with ~55,000, simply because you cannot squeeze all of the available electrons from 4 saturated pixels through the transfer electronics.

The final step is that the gain of the output stage is normally set to give 64000 ADU with only one pixel-full of electrons (25,500). With binning, it is presented with a bit more than double that many electrons per pixel, so the gain must be reduced by a roughly a half to keep the maximum reading to 64,000 ADU.

Last edited by Shiraz; 08-07-2014 at 01:54 PM.
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Old 08-07-2014, 01:06 PM
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Thanks Ray,
I had to read that 2-3 times, but I think I got it.

Bo
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