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Messages - dpaul

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61
General / Additive Stacking?
« on: 2018 February 20 16:47:29 »
One more question -

I have a large scope (30'') and the Atik Horizon CMOS mono camera - this is great camera for short exposures with low noise.
My scope is unguided on an equatorial platform so I can usually get up to 20 seconds decent tracking. With my large aperture this perfectly adequate for LRGB frames.
I've also tried with narrow band and results aren't too bad, managing to push the limit to about 25 seconds, just, but more would be nicer.

So here's my question -
I appreciate additive rather than average stacking when integrating frames is not a great idea from a S/N perspective. However if such a method is possible when image processing then I could get better results with these short frame lengths. With video astronomy additive stacking is quite common (great for outreach) but can Pixinsight so this in post processing?  If not I still think it could be a useful tool - hoping its possible!

Of course another option is 4x4 instead of 2x2 binning but I prefer the 2x2 pixel resolution.

Thanks

David


62
General / Color-Splitter type CMOS Chip vs RGB type
« on: 2018 February 20 16:34:48 »
Hi

I was reading about the benefits of using a color-splitter for CMOS chips to increase sensitivity, see link below:

https://petapixel.com/2013/02/05/panasonic-doubles-color-sensitivity-in-sensors-with-micro-color-splitters/

However, I'm presuming this means the traditional CFA pattern such as RGGB, BGGR, etc no longer applies. So here are a few questions for my interest:

1/. Can a color splitter chip be used for astro-imaging
2/. Assuming the answer to 1. is a yes, can Pixinsight handle the data in a debayering process?  If the answer to 1. is no then maybe the concept of debayering doesn't exist with color cameras that have color-splitter chips?

Thanks

David







63
General / Re: Color Calobration - Incorrect Color Outcome
« on: 2018 February 19 16:08:31 »
Hi Rick,

It doesn't sound very secure giving public info about dropbox, so I'm concerned about doing this 'on a forum'.

I did try one more time - this time I calibrated and registered all frames in one go. Previously I'd done the R,G<B and L separately then star aligned before RGB intregration.
The results are bit different, probably because I color calibrated slightly different - attached is this version.
Not so green.

Maybe I did mix up frames when saving the data from the camera? I did have a break when doing the blue due to temporary cloud cover.

Lets see how my next session goes.

thanks

David

64
General / Re: Color Calobration - Incorrect Color Outcome
« on: 2018 February 19 14:23:27 »

Hi Rick,

I checked the filter wheel just to make sure I had the right filters in the right positions - which was correct.
I've also tried linear fit (and nothing else), then tried color calibration (without linear fit) of each R,G and B integrated frames and finally tried Photometric Color calibration (without linear fit). The attached two images are the final results after merging with Lum and then stretching. V1 is color calibration, V2 is PCC.

As you can see, the results are quite green, the bar across the main galaxy in internet image sis always golden, not green. I tried SCNR which eliminated the green but also most of the color in general.

Thanks for everyone's help about better understanding of linear fit and when to do / no to do, etc. There is however still some fundamental issue with the color management. Its odd because other LRGB results seem quite good until now??

Thanks

David

65
General / Re: Color Calobration - Incorrect Color Outcome
« on: 2018 February 19 07:53:32 »
Thanks Rick,

With Linear fit, how do you physically select one color and compare it against the others?

The only option is to pick ''one'' reference image and apply to the ''one active image'' so I still don't know how to do this?

I also like Photometric Color calibration but its not easy to get it to work all the time. I've even had the same data working / not working on different days.

Thanks

David

66
General / Re: Color Calobration - Incorrect Color Outcome
« on: 2018 February 19 01:22:05 »
Hi Rob,

Sorry, I mixed up two issues (I have a separate issue with getting color after debayering on a one-shot color camera - see other post).
I meant to say it was mono camera - stupid me!

I've now read about linear fit and can see how it can match the R, G, and B channels before combining. However, non of the tutorials I've read say ''where to get the reference image from''. I've no idea what to do at all here, for eaxmple something from the internet that ''looks right'' for that same object.

Regarding color calibration, what would you use as the white reference instead of 1 star? I've seen people using a preview of a galaxy but what is that galaxy is muti-coloured?

Thanks

David

67
General / Color Calobration - Incorrect Color Outcome
« on: 2018 February 18 15:35:51 »
Hi

I'm having a frustrating time with color calibration today. This is using a one-shot color camera (Atik Horizon) and LRGB filters.

I've only recently started LRGB imaging and as can be seen from posts I did in the gallery section last week, in general my first attempts have shown reasonably good color balance.

That was until last night!

I was taking light frames of NGC 3718 and the resulting combined RGB image is too green. This galaxy should be more blue with a gold/yellow bar across it but that bar is green and not much evidence of blue.  I have calibrated each light frame with darks, bias and integrated them into separate R,G, B and L master ''linear'' images. I've then done star reduction using MT and deconvolution - all with use of star mask and luminance masks. Then I used channel combination to combine the ''still linear'' R,G, and B.

The resulting background when stretched was green (but I've seen that before in tutorials-I'm assuming that's ok?). Next step was to color calibrate so I first did background neutralisation which removed the green, then I used color calibration with two preview images (background without stars) and a bright star for whilte balance. The result was too green, nothing like images I've seen on the internet of this galaxy. I also tried photometric color calibration which at first worked then when I tried again later it refused to - but this still gave a similar result.

After stretching the RGB image with HT and increasing saturation with curves, I still cannot see anything but a green bar across this galaxy.

Must be doing something wrong?

David








68
General / Re: Debayering One-Shot Color data
« on: 2018 February 17 12:13:26 »
Hi Bernd,

I'll leave it for now - I'll see what comes back from Atik, that may help me.

Thanks

David

69
General / Re: Debayering One-Shot Color data
« on: 2018 February 17 06:31:07 »
Hi Bernd,

Thanks for the reply -

I can send a calibtared lightframe but how do I do this on the forum, the file size is 16Mb?

David

70
General / Re: Debayering One-Shot Color data
« on: 2018 February 17 02:04:15 »
Just one small correction - I meant to say AUTO or not AUTO working ''isn't an issue''

71
General / Debayering One-Shot Color data
« on: 2018 February 17 02:00:51 »
Can someone assist -

I've just started using the ATIK Horizon color camera (already have the mono and having good results with LRGB Imaging).
Im having problems converting the one-shot color data from raw to color via debayering.

The sensor is a Panasonic MN34230 4/3" CMOS.

This is the order of play which I 'think' is the correct procedure:  I calibrate the raw light frames then debayer each frame. Then I do star alignment and integration of the images. When debayering it doesn't recognise the CFA  (Error: Unable to acquire CFA pattern information: Unavailable or invalid image properties). However I switch from auto to a specific pattern (bayer/mosaic pattern) it then works. I don't currently know the pattern for sure but I think its BGGR (checking that directly with Atik). My understanding is that Auto used to work on earlier Pixinsight version but now it doesn't (not sure if that's correct?) - either way that's an issue.

So after registering and integrating the frames, the resultant RGB combined image seems to have little or no color. It doesn't matter whether I stretch the data, play around with the curves, try color colibration, etc, its just generally gray. The only coloor that seems to appear is the background gets light color when saturation is pushed to the limit. I've also tried looking at an individual debayered frame before intregration and that's the same. I've also tried non-calibrated frames and still the same.

I also tried every pattern in addition to BGGR and still no better (some gave a green hue overall) - still no general colors.  I was using VNG as the demosaicing method but bilinear and superpixel didn't work either.

Attached are the statistics (clippe dand unclipped) for a single raw frame that was debayered with BGGR / VNG (no calibration or registering) - doe sthis data look ok?

I have a 30'' scope and the frame length was 15 seconds - this is a lot of data with this aperature and proves more than enough with LRGB imaging so I'd be suprised if its a weak signal. Maybe I'm doing someing fundamentally wrong when saving the data but I'm saving RAW / FITS so I'd be surprised.

Thanks in advance for any assistance.

David












72
General / Re: FLATS QUESTION
« on: 2018 February 14 13:19:50 »
Thanks Mike / Rick

Regards

David

73
Gallery / Re: LRGB Images with Atik Horizon Mono Camera
« on: 2018 February 14 13:16:59 »
Hi Cho

Please see attached pictures of the 30'' scope, the RH view in on the equatorial platform.

Thanks

David

74
General / FLATS QUESTION
« on: 2018 February 14 01:51:28 »
Hi,

Presently I only take darks and bias frames and no flats. This is because I have to return my 30'' scope to a cabin after observing and the width of the entry means I can't leave a camera/filter wheel sticking out sideways, it will get knocked.

I'm aware of the importance of taking flats with the focus position remaining as per the light frame captures, also the camera rotation itself.
So here's my question:

How accurate must this position be? For example if I carefully remove the camera then return it to the scope the following day without adjusting the focuser 'and' noting the rotational position, will that be good enough. The rotation is probably the hardest to replicate but within 1 or 2 degress ok but no if it has to o.1 degrees?

Thanks

David

75
Gallery / Re: LRGB Images with Atik Horizon Mono Camera
« on: 2018 February 14 01:44:21 »
Thanks Rick,

Until now I've hesitated to post images on this amazing forum because the quality is so good from others - my results are mostly down to advice from the forum.

Regards

David

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