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Old 01-08-2012, 07:54 AM
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8300 sensor RGB binning questions

This came up in the QSI Yahoo! Group and thought I'd also post here.

Does anyone here shoot L unbinned and RGB binned with 8300 sensors? I'm trying to find out if it's a sensor thing, normal for RGB binning, or something I'm doing in terms of processing or perhaps even image capture times or number of subs.

Quote:
I'm keen to hear other experiences as well. I have a 583ws, and have found that the binned RGB is quite "blocky". I know the pixels are double the size and would expect them to be blocky in that respect, but it's more than that.

See these cropped images. The L is unbinned, the RGB is 2x2.

L: http://flic.kr/p/cHivQ5
RGB: http://flic.kr/p/cHivts

See how the binned RGB stars have a dark pixel perimeter, then lighten up again? When I do the L and RGB combination, this is evident. ie the smooth L doesn't smooth that out. The little brighter diffraction spike looking pixels are there and noticable.

As a result, I've taken to shooting 1x1 for RGB as well, but would love to be able to cut exposure times down by using binned.

I'm not sure if it's my processing, a property of the sensor (I'm sure I've read somewhere that this is common on the 8300 sensors, but haven't been able to research further), normal for combining 1x1 L and 2x2 RGB, or something else.

Perhaps it's my image capture technique? As I understand it, binned 2x2 has 4 times the gathering capability, so 1/4 of the exposure time is correct?
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Old 01-08-2012, 08:50 AM
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I've only ever used 1x1 binning with my SX H-18 after seeing horizontal blooming at 2x2. This is caused by the shallow horizontal shift register on the KAF8300 and can be reduced somewhat by dropping gain (some cameras appear to do this automatically when binning is used). There are some examples here: http://www.pbase.com/wjshaheen/horiz...he_kaf8300_ccd

Looks like a different issue to what you're talking about, Troy, but you may run into this as well. I don't think the KAF8300 design is well suited to binning.

Cheers,
Rick.
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Old 01-08-2012, 08:56 AM
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Aah, yes. I've seen that effect on really bright stars if binning and exposures too long. That is different to what I'm experiencing, though.

The QSI recommendation is to use high gain for 1x1 and low gain for binned. Even then I've seen that effect you mention on really bright stars.
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Old 01-08-2012, 01:34 PM
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Interesting. I binned my stf8300 2x2 with 5 min subs recently and had this horizontal blooming. It was realy annoying. I don't think you can lower gain on sbig drivers though.

Any other suggestions other than shorter subs?
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Old 01-08-2012, 09:34 PM
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Never seen that with my FLIML8300 so it must be controllable.

Greg.
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Old 01-08-2012, 10:11 PM
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Never seen that and have only recently (last two or so images) started doing 1x1 on all my channels. All other stuff has been 2x2 for colour and 1x1 for detail layer.
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Old 01-08-2012, 10:49 PM
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Not seen the effect with my QSI583
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Old 02-08-2012, 12:16 AM
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I've not seen it with my QSI583.

Paul - why did you change to 1x1?

DT
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Old 02-08-2012, 01:13 AM
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Ok, thanks guys. As usual, must be me.
Might do some more experimenting with the binning.
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Old 02-08-2012, 08:19 AM
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Quote:
Originally Posted by DavidTrap View Post
I've not seen it with my QSI583.

Paul - why did you change to 1x1?

DT
I know you asked Paul but if I can butt in. There is a regular debate about 1x1 on all channels veruss 1x1 on luminance only and 2x2 on colour.

The usual reasons for 2x2 on colour is that colour does not have sharp edges and more fading edges whereas luminance has sharp edges and requires extra resolution.

So 2x2 speeds up the acquisition process and also if you have poor seeing you are not losing anything anyway.

But for maximum resolution and in areas of good seeing and on objects where you want maximum detail (galaxies for example or globs or structures in nebs) 1x1 gives that extra. Its more suited to someone with a permanent observatory as the extra time required to get noise free channels is not so much of an issue.

Additionally some desaturate the RGB and add it to the luminance for a slight bit extra omph. I have not noticed that that technique adds much but every little bit counts.

1x1 is a moot point if you have poor seeing and you may as well shoot everything 2x2 especially a small pixelled camera like the 8300.

Not all cameras get the same gain on 2x2 but there always seems to be a gain. It isn't 4X though more like 2.0X. Richard Crisp did a paper about this recently measuring an 8300 chip for 2x2 performance. As I recall it ended up about 2X better signal to noise ratio using 2x2.

Greg.
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Old 02-08-2012, 08:23 AM
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Quote:
Originally Posted by DavidTrap View Post
I've not seen it with my QSI583.

Paul - why did you change to 1x1?

DT

David I simply changed to 1x1 to accommodate narrow band blending into my imaging. I have for a long time wanted to undertake comprehensive imaging projects. Using 1x1 just makes it simple.
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Old 02-08-2012, 08:48 AM
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Quote:
Originally Posted by gregbradley View Post
...
Not all cameras get the same gain on 2x2 but there always seems to be a gain. It isn't 4X though more like 2.0X. Richard Crisp did a paper about this recently measuring an 8300 chip for 2x2 performance. As I recall it ended up about 2X better signal to noise ratio using 2x2.
....
I found something similar, although nothing actually measured. Instead of 2x2 exposure times being 1/4 those of the 1x1 lum, I was going with 1/2 the exposure time. eg L at 1x1 was 4mins, I'd use 2x2 RGB at 2 mins instead of 1min.

Is that what you're saying?
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Old 02-08-2012, 01:52 PM
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Richard's analysis is here:
http://tech.groups.yahoo.com/group/F.../message/11264

The benefit of binning on the sensor is that you only get the same read noise for a binned super-pixel as you would get for a single pixel in 1x1 mode. So, for example, with 2x2 binning you are getting 4 times better SNR just considering read noise.

Richard's point is that you also need to consider shot noise and the improvement in that increases as the square root of the number of binned pixels - with 2x2 binning you only get a 2 times better SNR just considering shot noise.

In practice, the benefit is going depend on which of these factors is dominant. For very faint signals the benefit will be closer to 4 times and will decrease to approximately 2 times as the signal increases.

Richard also mentions the problem of saturation of the horizontal shift register which is what causes horizontal blooming on the KAF8300.

Cheers,
Rick.
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Old 02-08-2012, 02:02 PM
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While we have full moon at the moment I'm doing some experimenting.
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Old 02-08-2012, 02:10 PM
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Quote:
Originally Posted by Paul Haese View Post
David I simply changed to 1x1 to accommodate narrow band blending into my imaging. I have for a long time wanted to undertake comprehensive imaging projects. Using 1x1 just makes it simple.
Ta for that

So how long at your typical RGB subs at 2x2 vs 1x1?

DT
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Old 02-08-2012, 02:20 PM
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I was using 15 minutes at 2x2 and for some objects 10 minutes. At present I have been doing 10 minutes at 1x1 but that is likely to change at some point.
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Old 05-08-2012, 09:51 PM
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Today I did some experimenting and got to the bottom of the issues I was referring to above. Turned out to be the algorithm I was using in PixInsight to do the upscaling from 2x2 to match the 1x1 size.

If you're interested, if you use the BatchPreProcessing script, for the image registration section they use StarAlignment with the default algorithm of "auto" which is actually, I believe, is one of the Lanczos algorithms. Changed that to some others and tested, and the best result I found was Bicubic B-spline.

The above would also apply if you were using StarAlignment, not just the BPP script.
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Old 05-08-2012, 10:06 PM
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2x2 ok on my QHY9. In a perfect world I wouldn't resort to binning any of the RGB, but in reality its often tempting especially if seeing is questionable or shooting narrowband (S in particular).
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Old 10-08-2012, 01:23 AM
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Troy the problem with the 8300 sensor, no matter which camera, is that the readout buffer is a row of standard pixels with 25K well depth. If you read out a heavily exposed and binned image through those buffers, they will overflow and flood the Analogue/Digital Converter on the camera.

What Rick see's on his SX camera is an overload of the A/D converter which causes lines coming out from bright stars when you bin. The gain on the camera is set too high for binning and in SX cameras that gain is set via a pot on the cameras main board. In the QHY cameras they have a feature called clamping which switches in a diode on the A/D converter input and simply lops off hi levels above the clamping point.

Not sure what the others do but the problem is in the sensor itself and the readout buffer. I found it worked best to do 1x binning for everything but I know that's often not possible so next best is to figure out the binning multiplier and reduce binned subs by that factor. I mean, binned x 2 should be 4 times but it's not, it's probably closer to 2.5times. Take some shots of an G2V star and measure it.

So you might end up with 10 minute Lum binned x1 and 3minute RGB binned x2 to get the balance right.

Or buy a camera with a huge well depth and bypass all this crap
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Old 10-08-2012, 06:51 AM
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The big reason that binned subs are not 4 times the signal is that we usually bin RGB frames, and they are filtered shots. Therefor the signal is lower just because you are only capturing one channel. I am sure it is not 100 % efficient also.
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