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Where did all my colour go? - Woes of OSC CCD


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Also posted in PI forum

Having got and processed with reasonable success a few pictures with a dslr I got a while back an Atik 314L+ colour camera and still haven't managed to get anything from the data - I'd always blamed poor flats or lack of darks or something so last week I set about getting a full set of data and calibration data. I use Sequence Generator Pro for data aquisition. Got 30 Bias, 30 Flats, 11 darks and 18 lights (latter two at 1x1 bin 10minutes exposures -20degC camera temp) - (125mm refractor with 0.63 reducer if thats relevant)
Load everything up in PI batch preprocessing - I've tried all the different debayer patterns RGGB and BGGR give reasonable results that don't look much different. Other patterns seem to produce wierd background colours - the ticking or unticking of the upFIt box seems to make little difference although I suspect it should and I have no idea which option applies to my setup I'd guess it should be the amateur one.
Well I get a decent image out at the end - plenty of detail of the galaxy when STF autostretch is applied but there is no colour - nil - not in the galaxy or any of the stars, surely there should be something? I'm sure it wasn't like that when I processed the dslr pictures .. so where the hell has my colour gone. This is pretty much what happened with my previous attempts too. Getting to the point where the CCD could well end up thrown in the hedge and the dslr attached again .. Please I need help!!!
If anyone is interested all the files are shareable from my google drive - https://drive.google.com/folderview?id=0B7-WT0lTBlOtVmV1OXM4bExsaEU&usp=sharing hopefully the folder names should be obvious enough.
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Looking through your images the following problems were found:

1: In the Lights folder two of the images are flipped 180 degrees, in PixInsight all the images have to have the correct orientation for integration (stacking).

2: In the Flats folder all the images are grossly over-exposed and could not be used, if you are using an iPad or PC screen as the light source you need to reduce the light output by at least a half to three quarters, try placing a couple of sheets of 80-90gsm plain copier/printer paper over the screen and keep the exposure time the same, for flats generally, using a TFT laptop or iPad screen as the source you get better results going for an exposure time around half a second at least and dimming the light output of the light source with paper absorbers accordingly, the resulting image should look dark grey when un-stretched, yours are bright white and almost saturated.

3: In the Darks folder you seem to have a mixture of darks and flats, the darks were useable but the flats introduced artefacts which indicates they were not taken at the same time as the lights?

4: As Steve mentions above, your attached TIF file is not using the correct DeBayer matrix, for the Sony ICX285AQ CCD used in the Atik 314L+ and PixInsight the correct DeBayer mask to use in Batch Pre-processsing is GRBG with the "Up-Bottom" Fits box ticked.

Once you have calibrated and integrated the lights use the colour saturation tool in PixInsight to bring out the galaxy and star colour.

The attached image was roughly processed using all your lights and bias frames, five dark frames, no flats, and colour boosted using the colour saturation tool.

 

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Looking through your images the following problems were found:

1: In the Lights folder two of the images are flipped 180 degrees, in PixInsight all the images have to have the correct orientation for integration (stacking).

2: In the Flats folder all the images are grossly over-exposed and could not be used, if you are using an iPad or PC screen as the light source you need to reduce the light output by at least a half to three quarters, try placing a couple of sheets of 80-90gsm plain copier/printer paper over the screen and keep the exposure time the same, for flats generally, using a TFT laptop or iPad screen as the source you get better results going for an exposure time around half a second at least and dimming the light output of the light source with paper absorbers accordingly, the resulting image should look dark grey when un-stretched, yours are bright white and almost saturated.

3: In the Darks folder you seem to have a mixture of darks and flats, the darks were useable but the flats introduced artefacts which indicates they were not taken at the same time as the lights?

4: As Steve mentions above, your attached TIF file is not using the correct DeBayer matrix, for the Sony ICX285AQ CCD used in the Atik 314L+ and PixInsight the correct DeBayer mask to use in Batch Pre-processsing is GRBG with the "Up-Bottom" Fits box ticked.

Once you have calibrated and integrated the lights use the colour saturation tool in PixInsight to bring out the galaxy and star colour.

The attached image was roughly processed using all your lights and bias frames, five dark frames, no flats, and colour boosted using the colour saturation tool.

attachicon.gifImage08.jpg

An heroic post and superbly researched.

Olly

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Looking through your images the following problems were found:

1: In the Lights folder two of the images are flipped 180 degrees, in PixInsight all the images have to have the correct orientation for integration (stacking).

2: In the Flats folder all the images are grossly over-exposed and could not be used, if you are using an iPad or PC screen as the light source you need to reduce the light output by at least a half to three quarters, try placing a couple of sheets of 80-90gsm plain copier/printer paper over the screen and keep the exposure time the same, for flats generally, using a TFT laptop or iPad screen as the source you get better results going for an exposure time around half a second at least and dimming the light output of the light source with paper absorbers accordingly, the resulting image should look dark grey when un-stretched, yours are bright white and almost saturated.

3: In the Darks folder you seem to have a mixture of darks and flats, the darks were useable but the flats introduced artefacts which indicates they were not taken at the same time as the lights?

4: As Steve mentions above, your attached TIF file is not using the correct DeBayer matrix, for the Sony ICX285AQ CCD used in the Atik 314L+ and PixInsight the correct DeBayer mask to use in Batch Pre-processsing is GRBG with the "Up-Bottom" Fits box ticked.

Once you have calibrated and integrated the lights use the colour saturation tool in PixInsight to bring out the galaxy and star colour.

The attached image was roughly processed using all your lights and bias frames, five dark frames, no flats, and colour boosted using the colour saturation tool.

attachicon.gifImage08.jpg

Wow! Thank you Thank you Thank you

Lights - I did a meridian flip - that's why two of the lights are flipped 180 deg _ I assumed PI would sort this and realign when the batch preprocess registered them. 

Flats - I did do a flat calibration in Sequence Generator which showed the exposure used was correct - I'll have to investigate this further - I used a white cloth secured over the scope in daylight - I'll add a piece of paper too next time or use my ipad screen as I've done in the past

Darks - I took some before the lights and the rest next morning - I'll have to investigate why they're not right - cant explain that right now 

I'd suspected the debayer method was incorrect but I really couldn't find out what it should be so thank you again 

Now I'll go back to it and sort out the issues and get it right :) Was really losing enthusiasm and getting dispirited ... thank you for taking the time and trouble to help - you're a star.

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I've come back an hour or so later - still blown away that Oddsocks took so much trouble and gave me such a complete answer. There are some awesome people out there ! 

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Glad to have been some help.....

I can't say for certain but I think PixInsight can only auto flip the images in pre-processing if the telescope orientation data gets added to the fits image file header and not all image aquisition software does that, I allways check and flip + save manually before pre-processing otherwise PI will ignore those frames that are not orientated the same as the reference frame and drop them from the stack.

When you do your flats don't do them in daylight, thats probably where the aretefacts are coming from, in daylight too much light can leak into the light-path around the focuser draw tube, filter-wheel, screw holes in the tube for various fixings etc, take the flats in the dark and they will be fine.

There are several ways to check the exposure used for a flat is correct, the way I was taught in medical imaging was to first look at an unstretched dark frame and using the measuring tool provided in the processing software look at the highest average pixel ADU reading found that is not a hot pixel, for example it might be 117, then you quadruple that figure to give 468, and round up to the nearest 100 giving 500. Now take the unstretched flat frame and measure the darkest pixel visible that is neither a dead pixel or one covered by a artefact lying directly on top of the CCD, you can tell those because they will be sharply defined and have an ADU the same as a single dark frame, about 117, the flat exposure will be correct when the darkest pixel that is neither dead or obscured has an ADU of around 500. The maximum value in the flat will then be up to a thousand or more ADU's above that, the exact value is not important.

This is the method I carried over to astro imaging and it seems to work well for me, after a while you will be able to judge it by eye comparing a dark frame to a flat frame side by side the flat frame should appear only a little brighter than the dark frame.

Your souce data can reveal a much better image than the one I posted as I did not bother with star masks etc so keep going and don't get disheartened, CCD imaging has a slightly different set of processing steps than those used for a DSLR but once mastered the results can be quite amazing.

If you haven't seen them yet look at some of Harry's PixInsight tutorials at HarrysAstroShed

http://www.harrysastroshed.com

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Checked the FITS file headers - the rotation is in there and yes PI can align them. :) Flats were assessed using the SGP calibration wizard to get ADU to 30,000 - looking at the files in file explorer in PI the median s 0.65 and as the flats get higher in number the histogram moves to the right - I used the first 8 and experimented with using those 8 flats Vs no flats and with the flats there was a markedly less noticable gradient on the integrated file so I stuck with that. Had a go at processing and came up with these - pretty pleased with them for a first go but I have no doubt they could be improved a lot with experience and appropriate knowledge. 

16734844113_54ba67ddc5_o_d.jpg

17351617712_40169e55c4_o_d.jpg

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