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Old 24-01-2021, 12:44 PM
Martin Pugh
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Qhy600c

I have come across an interesting problem or perhaps error on my part.

If I take an unbinned image with this camera, I can calibrate it and debayer it and a colour image pops out.

If I take a bin 2x2 image with this camera, calibrate with the appropriate files, and debayer it colour, the image comes out black and white and only the residual noise in the image is coloured.

is this a procedural error or is this common knowledge.

regards
Martin
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  #2  
Old 24-01-2021, 04:30 PM
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I thought 2x2 binning combines the signal from the four adjacent RGGB pixels into one so the colour info would be lost.
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Old 24-01-2021, 05:19 PM
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multiweb (Marc)
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Quote:
Originally Posted by Martin Pugh View Post
If I take a bin 2x2 image with this camera, calibrate with the appropriate files, and debayer it colour, the image comes out black and white and only the residual noise in the image is coloured.

is this a procedural error or is this common knowledge.
If you bin 2x2 you collapse 4 pixels of the bayer matrix into 1 so you end up with a mono. That is half the width and height of the original.
I believe if you wanted to calibrate the binned file you'd have to bin your calibration frames as well.
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Old 24-01-2021, 06:42 PM
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Quote:
Originally Posted by Martin Pugh View Post
I have come across an interesting problem or perhaps error on my part.

If I take an unbinned image with this camera, I can calibrate it and debayer it and a colour image pops out.

If I take a bin 2x2 image with this camera, calibrate with the appropriate files, and debayer it colour, the image comes out black and white and only the residual noise in the image is coloured.

is this a procedural error or is this common knowledge.

regards
Martin
These CMOS cameras don't do hardware binning like CCDs. They do software binning.

The Bayer grid is 2x2 so I imagine that is why you are losing colour data.

Others who use CMOS colour cameras can confirm or not.

Greg.
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Old 24-01-2021, 06:51 PM
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Originally Posted by gregbradley View Post
These CMOS cameras don't do hardware binning like CCDs. They do software binning.

The Bayer grid is 2x2 so I imagine that is why you are losing colour data.

Others who use CMOS colour cameras can confirm or not.

Greg.
oh wow... so it does color binning as well? I read the FAQ but still didn't get it.
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Old 24-01-2021, 07:23 PM
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Originally Posted by peter_4059 View Post
I thought 2x2 binning combines the signal from the four adjacent RGGB pixels into one so the colour info would be lost.
This is it in a nutshell. If you want to 2x2 bin a OSC you have to capture in 1x1, debayer and then 2x2 bin. If you bin a OSC you’re combining the RGGB bayer into a single pixel so all colour information is lost (averaged). Doesn’t matter if it is CCD or CMOS as either way you’re still combing the red, green and blue data into a single pixel.
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Old 24-01-2021, 08:01 PM
Martin Pugh
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Yep, you are right Colin.

Got the word direct from Dr Qiu at QHY. A OSC camera cannot be used natively at 2x2 as you lose all the colour. So you have to capture 1x1, debayer, and then downsample to 2x2.

So if you think about this in another way:

On a scope with just 678mm focal length, the image scale is 1.14 arcsecs per pixel. So a good approach would be to bin the camera 2x2, which would help mask any guide errors or accommodate average seeing, and it would certainly quadruple your sensitivity without really noticing any loss in resolution.

Not worth it. I think I will sell this camera.

thanks for the input
Martin
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Old 30-01-2021, 02:36 PM
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My understanding is binning CMOS cameras is always done in software as the hardware doesn't accomodate binning (QHY294 is the exception).

When binned in software afterwards you don't get 4x the signal. Its way less. Some have reported no difference. There may be a slight gain but its not like a CCD that way.

If you binned it would be more for matching the seeing and smaller files.

Is there a SNR gain if you downsample? I have seen some nice images with a CDK14 and QHY600 in 2x2 binning. But I guess it was more to match the optics and seeing. You can also run these cameras in APSc mode with a ROI setting (I believe, but not sure how you do that). But the point is that is another way to get smaller file sizes for objects that don't need a larger field of view.

Greg.

Last edited by gregbradley; 31-01-2021 at 10:12 AM.
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