California Nebula - Kelling Heath Ha and DSLR

[JonH]

I think a processing session to 'pool' knowlage should be arranged for some time in the near future....

[mickw]

*Hijack alert*

That would be a hefty session and who would do the pooling

Folks have been using Registax, DSS, Iris, PI and PS to get good results

[JonH]

That's a good point, although I didn't mean quite as general as that...
More like the imaging session at Roberts when he spoke about pixinsight.

[Carole]

I hope I have the right files here:

this is the DSLR stacked file:
https://dl.dropbox.com/u/5730788/California%20Friday%20DSLR%2024%20x%205mins%20800%20ISO%20ED80.TIF

and this is the Ha stacked file:
https://dl.dropbox.com/u/5730788/California%20Thursday%20Atik%20Ha%206%20x%201200%20-10%20degrees.TIF

Both stacked but unprocessed you'll have to flip one of them over and align them. 

Carole

[Mac]

I hope I have the right files here:

Nope,

the top one is a 404.  
i.e. no file.

Bottom one is ok

Scratch that, the top one was probably still uploading, as it is 70Meg!!

Both are working now.

[Mac]

Oh the joys of rural broadband.

97 mins and counting.

[Carole]

OMG!

[MarkS]

Oh the joys of rural broadband.

97 mins and counting.

2.5min from my rural location ...

[MarkS]

The colour data from the DSLR data is a nightmare!  It just doesn't "feel right" to me at all - it doesn't respond in the usual way.  I can fully understand why you couldn't get star colours out of it. 

I really think that something strange has happened somewhere in DSS.  Before making a final judgement, I'd really like to see the same data stacked in IRIS - we must arrange this somehow.

Mark

[RobertM]

I would agree with Mark.

The background has come up much redder than I would expect plus the is a lot of horizontal banding.  It's also a lot noisier than I would have expected from that many subs.

Just a few thoughts - Can you check if there are any rogue subs i.e. those where any clouds may have crossed or short subs included accidentally.  It's important that all the subs are as identical in quality as possible.  Were the darks done at the same temperature ?

Robert

[Fay]

i would like a lesson in IRIS..................

Mark, i was having a practice and did not see how I could include my flat darks. is there a way?

[JonH]

I also also couldn't resist but have a play. Sorry, but i'm getting a little tired of looking at my M31!

As was said before, i found horizontal banding in the DSLR image and it seemed very noisy, although i did manage to eventually eek out the colour and calm the noise etc, possibly at a loss to fainter detail but i would still call it a respectable result.
As with the Ha one, it just did my head in! I could hardly get anything useful out of it and had i nightmare getting colour into it! But i possibly gave up to soon and it was my first ever play with an image from a monochrome camera...
As with combining them i would't even know where to start!

Like mark said, would be really good to have a look at a stack from Iris, or have the individual subs to play with as then i'd have a good idea on how to combine them and would like to see how they would work with some of the HDR stuff i have been messing with.
Perhaps at the meeting this Thursday (it is Thursday right?) You could bring it along on a memory stick any anyone interested in fiddling should bring a laptop and take a copy of the subs...

[MarkS]

i would like a lesson in IRIS..................

Mark, i was having a practice and did not see how I could include my flat darks. is there a way?

Yes - try this tutorial: 
http://www.saratogaskies.com/articles/cookbook/index.html

It's where I originally learnt to use Iris!

[MarkS]

Carole,

I don't normally do any post-processing in DSS except slide the colour channels together so they are on top of each other.  

I'm not familiar with it (I don't use DSS) but that's probably OK.

Unfortunately I was wrong!

I woke up in the night and realised what is going on in your image.  Those RGB sliders in DSS are very dangerous for the integrity of your data.  Don't touch them with a bargepole!  They apply a completely non-linear RGB transformation to the data and it is the wrong way to adjust for the RGB balance of your camera.  Sorry, I don't know DSS well enough to tell you the correct way to adjust colour balance.

Right click on this test image and save it to your machine
http://www.markshelley.co.uk/webdisk/Ramp.tif
It contains more than 50 shades of grey.    
There are no shades of any other colour.

Open it in DSS and adjust the RGB slider bars then resave it as something else.  Now open it in Photoshop or anything else where you read out the pixel values.  You'll notice that evey pixel now has a different colour i.e. a different ratio of R,G and B.  i.e. DSS has happily gone in there and introduced a whole range of colours that were not there before.  Conversely, when you adjusted the histograms so they were on top of one another, you unknowingly destroyed star colour that was previously there.

Try restacking in DSS and save your image without playing with slidey bars or anything else.  Put the result in dropbox and I'm sure we'll have sensible data we can play with!

This is just one example of the huge number of ways available to destroy the colour in your stars.  This is why I also bang on incessently about using the Iris asinh colour stretching to perform data stretch.  The Iris asinh function is the only function I know that stretches the data values whilst preserving the original ratios of R:G:B within each pixel.  If your stretch function is not preserving those original ratios then it is probably destroying valuable colour data.

If it's any consolation, PixInsight also does a excellent job of destroying star colour.  It's probably my lack of experience but I found that all the obvious ways of applying some kind of data stretch also changed the R:G:B ratios in the pixels

Mark

[Carole]

This is all very useful Mark, I have been wondering for some time whether DSS is doing the job properly, particularly as it sometimes doesn't apply flats properly, I have been wanting to find a different stacking programme for some time, but because I found both Maxim and Iris too complex and didn't have a paid copy of Nebulosity (and didn't want to fork out until I was sure I would be able to use it), I have been a bit stuck.  I have now got a tutorial for Maxim and am starting to learn this.  I will also take a look at Iris again now you have supplied a link and JonH has also sent me some useful info.

It seems daft to me to provide a tool in DSS (the colour adjustment tool) which has the result of destroying data and would explain why I have had a lot of problems with star colour.  

I will re-check all the subs for rogue ones, though I do normally check at the time of taking them (there is only a couple of hours subs in this stack by the way as I was just going to use it for the colour component of this image and not as a stand alone result.  

So looks like I have been fighting a losing battle for quite a long time. 

I am working today so will take a look at all this tonight.  Thanks for doing all this guys, and I think this is not only a very useful exercise for me, but might be something we could do on a regular basis, I am sure people like myself and new imagers would find using other people's data, particularly that of more experienced imagers a really useful exercise.

Thanks
Carole