#1  
Old 22-04-2016, 05:03 PM
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Question Pixel v pixel...who wins???

Folks,

I've recently been fortunate enough to have access to a couple of different sensors and had a go at trying to benchmark them, in the interests of science

The target was the keyhole/wedge area of Eta Carinae nebula, as it has both subtle and higher contrast features. Each image represents the same exposure time.

They are a fraction of the original images but to retain colour information I chose 24-bit PNGs and then had to squeeze them in to 200KB.

So...how to pick a winner from these?

Thoughts welcomed...

Cheers,
Dunk
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  #2  
Old 22-04-2016, 05:45 PM
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Just based on the pictures I see here, #2 looks the best to me. After looking at #2, the others seem blurry.
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Old 22-04-2016, 06:30 PM
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Post some calibrated FITS files and I'll run a few numbers for you, Dunk. It's difficult to judge processed data. I've made a few silk purses out of sow's ears

Cheers,
Rick.
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Old 22-04-2016, 06:36 PM
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#2 has the smallest pixels I assume, followed by #1 and then #3 getting larger.
#2 is the best resolved although I cannot figure out anything more than that
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Old 22-04-2016, 06:53 PM
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yep concur - #2
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Old 22-04-2016, 07:07 PM
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#2 for me also
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Old 22-04-2016, 07:17 PM
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And me.
raymo
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Old 22-04-2016, 08:26 PM
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Thanks all...it's so hard to look at them side by side on a computer screen and tell one from another

Note that these are all unprocessed - just stacked and with PI's STF applied (for its sins).

They were registered onto the mono image (the smallest) so that I'd be looking at the same field...does this introduce any gremlins of its own? As the camera rotation was not the same in each case, there would have been pixel rotation involved in registering.

But indeed, #2 is from the camera with the smallest pixels...5.2 microns...my modded Canon 1100D. The pixels in images 1 and 3 are about the same size at 6.5 microns, 1 being colour, 3 being mono. I was hoping to see some differentiation between the colour and mono at the same pixel size...the Loch Ness monster of increased resolution, or just variance in seeing perhaps?

I should add that these are what you experts call "under sampled", given my scope focal length is 550mm, but when the images were captured I suspect the seeing would have been better than my resolving capabilities.

@RickS - I did the same calibration on all of them...nil
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Old 22-04-2016, 08:36 PM
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Quote:
Originally Posted by Camelopardalis View Post
@RickS - I did the same calibration on all of them...nil
Fair enough, Dunk. That's better than doing a half-arsed calibration which will add noise
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Old 22-04-2016, 08:43 PM
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Phew...lucky escape

The mono CCD was cooled but not set point controlled. All three were taken at more or less the same ambient temperature, possibly a degree or two warmer the night the CCD images were taken.
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Old 22-04-2016, 08:50 PM
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Looking at them on my laptop instead of my iPhone (didn't even notice that two of them were colour!). #3 looks sharper (tighter) than #1 but #1 also looks like it has some elongation.
With #3 being mono it also has a greater dynamic range than #1 but that is mostly likely to be simply the difference between mono (filter) and any OSC.
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Old 22-04-2016, 09:20 PM
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Agreed...#1 is from a DSLR, as is 2

What I really need are some RGB subs...I (mistakenly) took some at 2x2 binning, and that really doesn't help the situation

Interesting re: elongation. PI judged the eccentricity to be larger. I must get my eyes checked!
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Old 23-04-2016, 06:08 AM
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That's a very interesting comparison Dunk.

To my eye, #2 is certainly the noisiest of the three, but also it has the tightest stars. Perhaps it would also be interesting, in the interests of science, to also compare a less bright region in all three?
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Old 23-04-2016, 08:16 AM
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Good question, Suavi...

Let's look at a less bright region of the frame, still with some features, but some darker areas.

Same order as before. STF applied to the full image (crop in the case of the DSLRs) before cropping to tiny images for upload.
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Old 23-04-2016, 09:49 PM
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Here are the stats I derived from single subs and the 30 minute stacks. Note that the single subs are 180s for the OSC cameras and 300s for the mono CCD, so I have estimated the SNR for a 2x180s stack for the OSC camera to give a number that is reasonably comparable.

Cheers,
Rick.
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Old 23-04-2016, 09:59 PM
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And here are comparison images of the three single subs with colour converted to luminance and image scale equalised.
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Old 24-04-2016, 07:59 AM
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Rick,
I think the oversampling in #2 is assisting in improving the resolution.
Great images!
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Old 24-04-2016, 09:34 AM
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It does show the gain you can expect by correctly matching your pixel size to your focal length and local seeing.

For the bulk of imagers 6 microns is that sweet spot.

Greg.
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Old 24-04-2016, 10:02 AM
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Quote:
Originally Posted by RickS View Post
Here are the stats I derived from single subs and the 30 minute stacks. Note that the single subs are 180s for the OSC cameras and 300s for the mono CCD, so I have estimated the SNR for a 2x180s stack for the OSC camera to give a number that is reasonably comparable.
That's awesome Rick thanks so much for taking the time out to analyse the data.

The old CCD, hereon known as "ol' faithful" really does walk away from the DSLRs. Cooling the DSLRs would make for some more interesting data points.

Quote:
Originally Posted by RickS View Post
And here are comparison images of the three single subs with colour converted to luminance and image scale equalised.
Wow, yeah not only is there a clear difference between the DSLRs, but the CCD still shows its mettle
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Old 24-04-2016, 02:24 PM
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First of all I'm only into observing so most of the details discussed in this thread are well out of my depth.

But base purely on looking at both sets of 3 pics, I like #2 best for stars and #1 from each set for the gas. The 1s seem to have the sharpest edges between the gas and background sky.

Great effort irrespective.

Cheers

Adam
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