M7 Wide Field - Image Processing Challenge

[jase (Jason)]

I can proudly exclaim that there is no light pollution in this data. It was collected from a rural dark sky location (as is most of my data). What you’re seeing is natural. Tens of thousands of stars from our rich MilkyWay. The yellowish/gold tint is produced from interstellar dust extinction.

[avandonk]

Here is a pseudo HDR image.

1 Digital development of fits files
2 Pixel math x0.66 for green
3 Recombine with images plus to produce colour tiff image

This was done three times to produce three images the only difference being the break point was doubled each time. This result is three tiff images a 'stop' apart.

These three were then cropped identically to get rid of non image edges with Images Plus under Image File Operations then choose Crop Files. This was done as otherwise you get floating point errors etc in EasyHDR.

These three images were then used to produce a LDR image from a HDR image generated in Easy HDR.
Levels adjusted in PS and GradientXterminator applied as before and RL in Images Plus.
Converted to JPG (90%) with IP and it is interesting the image is now 6.5MB.

Here
http://avandonkbl.bigblog.com.au/dat...0731091123.jpg
I think the colour is better.
Thanks again Jase. I have learned a bit more about this black art called image processing.

Bert

[iceman (Mike)]

I think that's your best yet, Bert. The colours are probably still a bit muted (to my preference) but nice job.

[jase (Jason)]

Incredibly sharp Bert. As Mike states, the foreground star colours a still a little muted. Background stars are looking great. You could do the trick I use when combining Ha and RGB data. Typically when you combine the two data sets, stars go crazy. So I copy the original RGB data that has been subtly stretched and saturated to bring out the star colours. Make this a new layer mask (hide all). Then simply highlight the stars on the mask layer. This will bring them out in their natural colour and dimensions without compromising the nebulosity or star field. This is one of many options. Certainly your best to date.

[Ingo]

Originally Posted by jase

I can proudly exclaim that there is no light pollution in this data. It was collected from a rural dark sky location (as is most of my data). What you’re seeing is natural. Tens of thousands of stars from our rich MilkyWay. The yellowish/gold tint is produced from interstellar dust extinction.

Very nice. I wish I had 0 light pollution

[jase (Jason)]

Bert, I thought about your processing further. In particular the LDR/HDR process. I’m not too sure if this is suited to such a wide field vista that contains only stars. As the process is taking into consideration the entire frame, key features such as M7 are muted. I’m wondering if you would get a different result if you cropped M7 so there isn’t as much of the surrounding star field in the frame and ran the same LDR/HDR process. This may produce an improved image of M7. If the results are desirable, you could then blend the improved M7 image into the greater wide field vista.

[avandonk]

Jase the HDR process really needs exposures that really are stops apart. Not fudged like this is. But you can see how it helps. The brighter stars really need the shortest exposure to capture their colour. Our visual system has a logarhymic response and it it hard to simulate with what is essentially linear data cobbled together after distorting its linearity.
I am surprised it even came out a well as it did. Still it is interesting what can be done.

Bert

[jase (Jason)]

Yep, I understand what you mean. You need to have differing exposures for the HDR process. Thus, CCD work does not lend itself to HDR work very well. Sure you could capture maybe 5min, 10min and 15min exposures, but this isn't the typical methodology used for long exposure CCD work. As CCD's response to light is linear, the DSO imaging trend is longer and longer subs. 15mins today, 30mins tomorrow. None the less, its good to try these processing tasks out to see what is capable.

[avandonk]

Just a few further thoughts.

Jase I also should mention that your camera has 16 bit dynamic range ie 65K odd levels whereas my Canon sensor is limited to 12 bits ie 4K levels by the A to D converter. To get the same dynamic range coverage with the Canon sensor as your camera I would have to take at least three images two stops apart. That is why I have been trying EasyHDR.
This of course assumes the target has this high dynamic range to make it worthwhile.

I think the real problem is trying to squeeze either 12bit or 16 bit linear information into an 8 bit log jpg and have the intensity distribution match our eyes logarhythmic sensitivity. All the while maintaining or attaining colour balance! This is what image processing is really about!?

Bert

[tornado33]

Heres my effort.
I used Iris (its freeware ), turned the .fit into.pic (the file format Iris uses)played with the colour balance till it looked okay, but only ended up cutting back the green a small amount, .66 seemed too much with Iris. Used the Dynamic Stretching function to bring out the background without blowing out the brighter areas too much. Finished it off with Levels in Photoshop .

If I won lotto Id have an STL11 with the Adaptive Optics acessory on my telescope and lenses in a flash
Scott

[jase (Jason)]

Well done Scott. You've made the star cloud very rich looking. Though in the process have lost much of the star colours. The image appears to take on a mono-tone feel.

[tornado33]

Thanks
Heres another go but this time using the "colour stretch" function in Iris as well. Bit of colour in the bright stars now
Scott