PixInsight > Image Processing Challenges

OSC of horsehead


Hi everyone - my first post to this forum so I hope I havn't broken any rules and that my question is appropriate - if not, I apologise. I am very new to astrophotography but managed to get a photo of my dream target - the horsehead nebula (attached). That said, I use a canon DSLR, so no filters - just point and click. The result is that the image has no contrast and I was wondering if, using pixinsight, it is possible to make the nebula more black and have it stand out from the background so I'm not having to explain to non astronomical friends what the picture is. I've been playing with it for a couple of weeks with very little success. Any guidance/list of instructions on how to do this would be really appreciated.

Many thanks


Hello, I am not an experienced PI user, but have Canon dSLR.
You can get a better image if you can get many images of the same target, and combine them. Its called " image stacking". Then you can process the results to get the image. Its not that hard but you need to learn about - light frames, dark frames, bias, flats.
You have quite good result in the single frame, thats good.
After adjusting the image- even out the brightness, adjust levels, background neutralisation, colour adjustments, then histogram stretching, then final adjustments for colour, saturation, exposure..

There is a lot.
But I am no expert.
You can check out - youtube tutorials - processing astro RAW files..

Thank you for your reply - yes I have been reading up on light frames, dark frames etc. - very overwhelming but we'll get there :-). I'm in the process of looking at the tutorials...

Not sure how your reading is coming along... but here are a few things to consider.

1. Normally, when you take a picture in daylight or with a flash, you have a TON of light that the sensor captures.
2. Now you point to the Horsehead Nebula, and your camera says: "Ack, no light" - and you (or the camera recommends that you) start tweaking the camera settings to compensate for the low light.  You bump up the ISO, and you increase your exposure time.  Maybe you open your aperture. 
3. Now, you take a picture, and look at your screen, and lo! you start seeing some nebula!  Wonderful.  If this were daylight photography, you'd be set.  But, alas, your work is not done.  Your camera has fooled you into boosting settings that actually need to be removed (or at least accounted for properly) 
4.  All the "stuff" that needs to be removed are what you reading up on. 
5.  Bias Frame - a picture of the noise your sensor produces all the time, for every picture, regardless of exposure time or ISO.
6.  Dark Frame - a picture of the noise your sensor produces at a specific ISO and shutter speed.
7.  Flat Frame - a picture taken of a plain white subject (like a wall) that shows the dust motes and vignetting.
8.  Light Frame - your wonderful picture of Horsehead.

The quick story:  Take your Light frame, remove all the noise from the dark frame, remove all the noise from the bias frame, increase the brightness where there was dust motes or vignetting, and voila!.

But, the sky deceived you too, not just the camera.  The stars look bright, but in comparison to the nebula, they are VERY bright.  The atmosphere is swirling around above you and smearing the light on your sensor as it comes from the star.  The moonlight or the ambient light pollution is being recorded in the picture.  All these problems need to be removed too.  The best way to combat that is with lots of pictures of the Horsehead.  Like, maybe 100 of them! 

So, PI will help you with all this by merging together your 100 pictures (ImageIntegration is the process, also referred to as "stacking") and figuring out what is "real" e.g. your "signal" and rejecting what is transient, or "noise".  PI can work with a very few number of pictures (lights) but the more you have, the better it can determine, and therefore reject, the noise. 

Some of the other tools that can help after stacking are noise reduction tools, background removal (e.g. moonlight/light pollution), and contrast/brightness tools like HistogramTransformation. 

Because your image is a single image, it's hard to remove much of the noise, but I did take a stab at doing a little noise reduction, plus some contrast adjustments.  Attached is my version.

BTW, aside from the online help, there are a few good old fashioned books out there on PI and astrophotography, which have been immensely helpful for me.  Sometimes a sit on the couch with a book and cup of coffee are a great way to just learn the background, and fundamentals so that when you sit back down at the keyboard you have a bit more direction.



Hi Dave - thank you so much for your comprehensive reply (sorry for the delay in responding - been away on holiday). Everything I'm reading is really helping me with the big picture....
Like what you've done to improve the image :-)

Many thanks


[0] Message Index

Go to full version