Image Processing Techniuqes 02

There may be many entries regarding "Image Processing" so I'm putting a number to the title. I may not be always put up step by step workflow for people to follow, but rather my thoughts on some issues.

(If you want any step by step stuff, regarding any techniques I've used or mentioned, you can contact me personally by leaving a comment, or by whatever means you can think of)

I have noticed I am having a trend in processing. Whenever I post anything to a US forum or mailing list, quite a number of people would compliment on the colour rendition of my images. Well, as I've stated in on of the processing workshops a few years before, one super important element in processing is to have a well trained or calibrated eye and mind. If you know what would look good, then definitely you are on your way. You just have to learn and practice the tricks and tools in your software and things will come in naturally. But as I see in most forums, people just don't know what makes an image look good.

Of course looking good is pretty subjective, but there are still a few key components that are generally accepted among amateur astronomers.

- low noise/grain, without cutting out fine details.
- small star size when shooting anything below 500mm (that is a signature for higher resolution)
- a large image scale (large number of pixels) -- this would usually violate with the low noise point, because resizing is usually the most convenient way of hiding the noise.
- good colour balance and contrast stretch

The first 3 points have a lot to do with image acquisition itself. It goes back to all those basics:

- having enough exposure: one good benchmark would be shooting at least for an hour with an F4 system -- you are guaranteed to have a decent image if you are shooting under a site with limiting 5.5 mag. (Although I had success shooting only 40min with F5.6... parental guidance needed for this kind of exposure)

- correct focus: Spend as long as you want to try to reach the best focus

- accurate tracking and guiding: this one is usually much less of a problem nowadays as the polar scopes are getting easier to use, and a longest 15min digital subframe would not need terribly accurate polar alignment


The last point on colour and contrast is the only part with nothing to do with the camera. On the contrary to public believes, I don't think it can really be taught. It is a matter of looking a a lot of pictures and decide which you would like, and then learn the methods to achieve that specific result. I can teach you step by step on all the things I've done to a certain image, but you won't be able to achieve the same result with another using the same tools and steps. The only way of doing it is through practice and training the eye.

Improvement

It is always a good idea to keep your raw and image calibration files well, because some day when you dig it up you'll realize that you can do a much better job on it.

The image on top is a new version of the image below. The stars are in much better shaped, and the background looks much cleaner without the residual effects of minimum filter. THe serious clipping of the lower image is also solved together with the weird colour balance.

That marks some improvement in my image processing techniques.

Cygnus and Neighbourhood

Camera: 350D modified
Lens: Canon 135 F2 Wide open, on ball head Manfrotto 308RC
Mount: EM11USD3 manual guide, GA4
Guidescope: FS60C
Exposure: 2 pane mosaic, each pane ISO400 5min x 6

Everything went wrong for this picture.

I did not have sole ownership of the mount, so the things I did were in quite a rush. That cost me the essential accurate focus and also a more accurate framing. The texture of the photo is disastrous and it can hardly be recovered by processing techniques.

Also when compared to the photos taken in Taiwan, those taken in XinJiang showed obviously more nose due to the temperature difference. I estimate the temperature up on the Taiwan mountains are a bit more than 0, yet in the desert ngiht it was around 20-25 Celcius.

A matter of 20 degrees made a huge difference in image quality.

XingJiang Mosaic M31

Camera: 350D modified
Lens: Canon 400F5.6 Wide open
Mount: EM11USD3 manual guide, GA4
Guidescope: FS60C
Exposure: 2 pane mosaic, each 5min x7

Guess what, I had different focus between these 2 panes... the right pane focus was a bit off and hence the colour balance and star size is different in the raws. I spent a lot of time correcting and cheating my way to make it even...

Otherwise this is my first respectable M31 taken. The texture was quite good, also the colour balance. The same to all other images, I could have increased the exposure to like 2 hours each pane for an even better result. I could have also taken some short exposures of teh center part. However that night it was a mess as different factors came to interrupt.. also my body condition was not good enough to focus so intensively. I made quite a number of mistakes that night.

XinJiang M17

Camera: 350D modified
Lens: Canon 400F5.6 Wide open
Mount: EM11USD3 manual guide, GA4
Guidescope: FS60C
Exposure: 5min x8

This is a test shot of the 400mm lens. It seems it is up to the job of providing a super lightweight option for digital medium focal length astrophotography. The stars are tight round up to the corners. It is reasonably fast at the price, size, and focal length.

This photo's guiding is off... the stars drifted all the 8 frames without an apparent reason. When I point the mount to another object, the problem was gone. I had to use post-processign to "cheat" the stars back to a round shape.

The image quality is just so-so because of the relatively short exposure time (I prefer at least a 2-hour shot for F5.6) and the misguided stars. The focus seems to be easier to reach compared to the F2 lens (due to the smaller aperture). But next time I still need to check it much more carefully.

Milkyway Center

Camera: 350D modified
Lens: Canon 135 F2 Wide open, on ball head Manfrotto 308RC
Mount: EM11USD3 manual guide, GA4
Guidescope: FS60C
Exposure: 4 pane mosaic, each pane ISO400 4min x 3

There is a little catch in this lens, which made me fail in my imaging in the later XinJiang trip. The key to focus the 135 lens is, despite traditional wisdom, not trying to cease the moment of the smallest chromatic abberration. So on the contrary, when the lens is focused, there is a very tight red/magneta halo around the stars. Also, it is CRITICAL to focus this lens properly, otherwise the whole texture of the image would fall apart, no matter how small the out-focused distance is.

With the above image (also the RHO complex one), I eliminated the red halo with post processing in Photoshop.

Again, I was so surprised by the outcome of the image. this image was not very well preliminary planned before the trip; it just happened when I try to get a shot of M8M20 and I realized I could try to do such a mosaic. Another surprise came to the quality of the image despite the 12min exposure of each frame. That may have to do with the low temperature on the mountain top, and also the large aperture of the lens.

I'm ow so desperate to get the films scanned... but I still don't have time yet.

Minute M31

Camera: 350D modified
Lens: Canon 135 F2 Wide open, on ball head Manfrotto 308RC
Mount: EM11USD3 manual guide, GA4
Guidescope: FS60C
Exposure: 5min x 7

This is a photo showing the quality of the 135mm lens. The corners are tack sharp, and the resolution is high with the M31 in the middle. I don't udnerstand why the colour of the Ha emissions inside the M31 is not shown. Nothing much could be improved maybe except increasing the exposure.

One can imagine that a 35min exposure on an F2 system equals to a 140min exposure on an F4 system.

Rho-Ophiuchus Complex

Camera: 350D modified

Lens: Canon 135 F2 Wide open, on ball head Manfrotto 308RC

Mount: EM11USD3 manual guide, GA4

Guidescope: FS60C

Exposure: 2 pane mosaic, each pane ISO400 5min x 4 + ISO 800 5min x 4

A successful piece overall, with slightly framing off a little bit than I'd expected. This was originally planned to be a 4-pane mosaic, but due to the problem of camera rotation I could only make 2.

The lens 135 F.2 is a beast, which means it is very hard to control yet if it is controlled you can get a stunning picture quality, at least with APS-C format. She is one of the reasons why I may consider 50D over 5DII in the future, because her abberration @F2 is super small when compared to similar lenses. It is also possible my copy of the lens is an exceptionally good one.

Next time if I am to shoot this object again I'll definitely go for 4 or more panes, regardless of the orientation of the camera.

The colour balance of the 2 frames may be a bit different.. I'll try to tweak them when I have time.

Evaluation on astrophotos taken in 2008

I've taken quite a number of astro pictures this year due to my Taiwan and Xinjiang trip. I'm going to evaluate them, either long or short, one by one.

Photos I have finished processing:

A -- Taiwan
1) Rho-Ophiuchus Complex
2) Centre of Milkyway
3) Minute M31

B -- XinJiang
1) M17
2) M31
3) NGC7000 and Cygnus Gamma
4) M8 M20
4) Totality

Thoughts on New Canon 5D MkII (and other possible body candidates)

This piece of news brought me a thoughtful night.


It is obvious that my modified 350D can no longer gives me a satisfactory performance in daily usage. The autofocus capability causes the most problem as I always struggle to achieve focus (again, in daily usage). The screen is small, it is slow, the viewing window is small, it does not have liveview focus.... (plus 1000 more reasons).

So the verdict is I'm going to get a new camera body. The problem is what to get, and here are my thoughts.

I once thought of selling my 350D to finance another (with live view) body for modification, and then buy another one for daily use. Then I recognize liveview is not crucial for focusing, it is just less convenient and more time consuming without. If I keep my 350D, I would just concentrate on getting a body for daily imaging and perhaps modify it after 2 product cycles. BTW I have considered the older models like 40D, or 5DI and have them modified right away for both astro and daily use.

Also, I'm highly tempted to get one of the latest Canon models like 50D and 5DII, because they are almost tripling the quantum efficiency of 350D, and doubling in that of 5D, thanks to the new CMOS and micro lense technology which leaves almost no gaps between the pixels.

There are also other concerns on a full frame machine because, while my current lenses are doing extremely well on APS format, may not perform as well on full frame. If I get the 5DII it could be solved because i can simply crop it or work on a mosaic and still there are a lot of pixels left (21 Million in total!)

There are so many options that I can come up with:

Plan A: Selling modified 350D
1) 40D modified
2) 5DI modified
3) 1000D modified + 50D unmodified
4) 1000D modified + 5DII unmodified

Plan B: Keeping 350D
1) 50D unmodified
2) 5DII unmodified

Notice I tend not to have the newest bodies modified (yet)

Australia Trip 2009 I

There will be a chance that I'll be going down under again next year for some holidays during July to August. So I'll be dealing with some Milkyway objects again. Yaye~!

The place I'm going may not be too far in the South, so the chance of getting a really high up Eta Carina is not that big. However, it will be winter time of theirs when I arrive so there'll be plenty of dark hours.

However there is another concern. If I'm going to that, it means that I'll very probably miss the solar eclipse thing in Shanghai, since the moon age will be a concern. Also, I cannot wait for the next new moon because I have school duties by the end of August and also there is a really important performance I have to prepare for... Also I could not be shooting the Eta Carina. If I do go in August, I'll be shooting both Scorpio and Orion IN THE SAME NIGHT (Kinda cool!).

I am now kind of torn between 2.


Now on second thought very probably I'll be going in July and miss the solar eclipse (not a big fat chance for clear sky anyway...)



Well, anyway, the trip is not entirely decided by me only haha

Processing Techniques

Last night I've read from a local forum that someone would, very kindly, like to use his middle finger to salute to those pks* who would not like to share their image processing technique. (The line was deleted this morning)

Well I believe I'm pretty sure I'll be one of those "pks" in his mind after I've read this. However, I had given two presentations on processing techniques and posted some steps on some of the processing techniques I discovered/developed myself a few years ago (Just that he didn't find it doesn't mean I did not do it).


The above 2 paragraphs are just some nonsense because I have taken the line ever so lightly and I'm just pretending I'm "filling the seat according to the number" =P
The fact is I do like to systematically write down and share my thoughts and findings to the locals on image processing. One of the major problems is I don't feel comfortable talking about something I have learned so easily and readily from others on the Internet. I'm still learning and reinforcing my knowledge day by day. It is ok for me to post some tips every now and then , but I am still not ready to give a full explanation on the stuff that I know.

A lot of the things I know may be wrong.

Let's see what people are asking for and adjust then


* meaning bastard in cantonese; literally means the person who fall down on the street while walking.

Evaluation on Solar Eclipse 2008

Call me a perfectionist.


I'm not really satisfied with the result which I got from the 2008 eclipse. Actually I could easily pick up a few things I haven't done well:

1)The focus was not tack sharp because I did not bother to check it really closely before the eclipse

2) I simply did not know how long the longest exposure was... I thought it was 2 seconds, but it turned out to be 0.8 only

3) I'm still struggling on how to bring out the inner most corona with a nice balance with the outer most part. At this moment the inner part is still too bright:





4) There was DUST either on CCD or the lens and I had a hard time processing them away. Remember to take flatfields next time....

5) I thought the Canon 400mm f/5.6 lens was long enough. With a crop factor of 1.6X I got a nice framing of the outer corona at 640mm. But after I got home I realized it was not something I was looking for... I like high resolution inner corona shots (of course some outer corona wouldn't hurt =P)



Well yeah, I know my pictures looked quite lovely and it seems that I did quite well on my first eclipse, but I have to realize that I might not have many other chances goign on an eclipse trip like this. I must treasure all my opportunities.

Testing

Testing...

This is a blog hoping to replace my multi purposed xanga which does not support large picture attachments...

This whole blog will be dedicated to astronomy.