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Old 25-06-2018, 10:23 AM
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Lognic04 (Logan)
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Binning RGB

Should i bin RGB 2x2 to get colour faster? The theory is that the Lum will keep the detail and rgb only needs to be roughly there.
Is this a good strategy?
Thanks!
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Old 25-06-2018, 11:15 AM
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Atmos (Colin)
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With your ASI1600, it makes no difference. Binning works with CCD’s but the way CMOS architecture works, binning doesn’t help
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Old 25-06-2018, 11:59 AM
kens (Ken)
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You can try using higher gain with RGB to reduce the exposure times but wherever you saturate all 3 channels you will end up with white instead of color. If only one channel saturates its color contribution is diminished.
By the way, are familiar with the concept of burying/swamping the read noise?
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Old 25-06-2018, 12:12 PM
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So its worth it increasing the gain till just before one of the channels clips?
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Old 25-06-2018, 12:48 PM
Imme (Jon)
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Quote:
Originally Posted by kens View Post
By the way, are familiar with the concept of burying/swamping the read noise?
I think this is a very important point
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Old 25-06-2018, 05:50 PM
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I have even heard that lum exposures need to be shorter than rgb to not burn out stars. I feel like you would already be using quite short lum exposures but your RGB would be even shorter?
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Old 25-06-2018, 06:14 PM
kens (Ken)
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Quote:
Originally Posted by Stonius View Post
So its worth it increasing the gain till just before one of the channels clips?
Its almost impossible to avoid clipping on bright stars so I'd qualify that to say you should avoid excessive clipping on your target. And if you can get a reasonable exposure time without any clipping that's ok too.
Because I'm in a light polluted area I need to be sparing with gain so lately I've been capturing just RGB and not bothering with L at all.
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Old 25-06-2018, 07:36 PM
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Because software binning (used in the 1600) forces data from (say) 4 pixels into one pixel, it increases the pixel-level SNR by 2x. But then your software will resample the binned RGB to blow it back up to the scale of the Lum for LRGB combination - so you get back sort of to where you started, although fine RGB detail will have been lost and the RGB will be a lot less noisy. Since the binning/resampling process reduces noise, you could get by with lower quality (quicker) RGB data.

However, filtering can also get rid of some noise, so it is probably just as effective to run a smoothing filter over the RGB to reduce the noise.

To check that I haven't got this wrong, I just processed an image that started out with noise of ~340ADU. Binned it 2x2 to give the (expected) noise of ~ 170ADU. Then resampled with the Lanczos algorithm to get back to the original image scale. The final image had less detail, but the noise was ~155ADU - so the binning/resampling process certainly improved the SNR. However, I got a similar looking result, but with noise of only ~130ADU by running a 3x3 median filter over the original image. ie, Don't bother with software binning to improve RGB SNR - just filter it.

Your overall strategy of trying to get by with less detailed RGB is helpful in some circumstances. I just processed an image where I had many hours of luminance, but the clouds meant that I could only get 12 minutes each of RGB. The RGB was very noisy but, with heavy filtering before combining with the L, the LRGB image came out quite well.

Last edited by Shiraz; 26-06-2018 at 07:15 AM.
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Old 26-06-2018, 11:17 AM
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Thanks all! i will not use binning for my RGB and just blur it in software.
Should i shoot RGB first then Lum? Have to carefully plan my time at a dark site imaging! Also, maybe 30 mins each of RGB would be idea?
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Old 26-06-2018, 12:06 PM
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I accidentally processed an image from last night in SuperPixel in PI - that's basically binning.

I just reprocessed it in my usual VNG.

I'll post a comparison.
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Old 26-06-2018, 12:34 PM
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Quote:
Originally Posted by Lognic04 View Post
Thanks all! i will not use binning for my RGB and just blur it in software.
Should i shoot RGB first then Lum? Have to carefully plan my time at a dark site imaging! Also, maybe 30 mins each of RGB would be idea?
Take your dslr just in case things dont work☺

I look forward to a happy result so good luck.

Alex
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