Easy 2D Signal-to-Noise Ratio (SNR) calculation for images to find potential stars without extracting the background noise

Long story short - I was looking for a way to detect more or less reliably if a user selected a region which contains a star. I wanted to be able to clearly distinguish between the following two images:

After a long journey I finally ended up with the following working solution based on the CImg library:

For the two images above the code gives the following results:

For many people this is where the journey ends. But for some of you it may just begin 🙂 Follow me into the rabbit hole and find out why the solution shown above actually works…

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NGC2175 from La Palma

Date2019/01/09
LocationLa Palma / Spain
ObjectOpen cluster NGC2175
CameraAtik383L+
Guidingyes, QHY5-II Mono via OAG
Telescope8
Barlow lensnone
MountEQ6 Syntrek
Cooling-10°C
Luminance8x 600s, bin: 1x1
Red7x 150s, bin: 2x2
Green7x 150s, bin: 2x2
Blue7x 150s, bin: 2x2
Dark2x
Flat10x
Total exposure~2h13m

On Wednesday, 9th January I imaged the open cluster NGC2175 the first time from La Palma. The seeing tonight again was very good - around 1.5~2"!

For post-processing I used the free software DeepSkyStacker and GIMP.

The full resolution images is available here.

Clear skies!

Milky Way - A longer exposure image

Date2019/02/01
LocationLa Palma / Spain
ObjectMilky Way
CameraEOS6D + Samyang 2.8/14mm
Guidingno
Telescope-
Barlow lensnone
MountEQ6 Syntrek
Cooling-
Luminance6x
Red-
Green-
Blue-
Dark3x
Flat-
Total exposure~15min.

Once more back on La Palma / Spain. I imaged the Milky Way a few times before from this beautiful location. However, up to now I was always bound to a maximum exposure time of about 20 seconds due to the earth rotation. This time I decided to put the camera - an EOS6D with a Samyang 2.8/14mm lens - on top of an EQ6 mount. This way much longer exposure times with a lower ISO value (i.e. less noise in the image) were possible without getting any star trails. I took 6 frames with ISO 1600 á 148 seconds each. The total exposure time is therefore about 15 minutes.

The frames were then post-processed with rawtherapee and averaged using the ImageMagick "convert" tool. In addition 4 frames of the foreground (the house) were taken and also averaged (of course with disabled EQ6 mount). Finally the two pictures were overlaid and merged with the help of a mask using gimp.

To me it is amazing to see the Andromeda Galaxy (M31), the California Nebula (NGC1499), the Orion Nebula (M42), the Pleiades (M45) and the Horsehead Nebula (B33) clearly on this photo. This overview picture gives a good idea of the brightness, size and exact location of the objects compared to each other.

A full resolution image of the result can be found here. Another image without object descriptions can be found here. I am curious to repeat this procedure in summer when the bright part of the Milky Way will be visible again 🙂

Andromeda Galaxy (M31) - The first time from La Palma

Date2018/31/31
LocationLa Palma / Spain
ObjectAndromeda Galaxy (M31)
CameraAtik383L+
Guidingyes, QHY5-II Mono via OAG
Telescope8
Barlow lensnone
MountEQ6 Syntrek
Cooling-10°C
Luminance6x 600s, bin: 1x1
Red5x 150s, bin: 2x2
Green5x 150s, bin: 2x2
Blue5x 150s, bin: 2x2
Dark2x
Flat10x
Total exposure~1h38m

Tonight I again decided to image the Andromeda Galaxy (M31) - the first time from La Palma. The seeing tonight was very good - around 1.5~2" which was extraordinary! Also the weather conditions as shown by La Palma HDMeteo were excellent.

Back in 2013 I already imaged the Andromeda Galaxy with the same equipment but from Boeblingen. It is interesting to see the difference here.

For post-processing I used the free software DeepSkyStacker and GIMP.

The full resolution images is available here.

Clear skies!

Blood moon at Lake Constance

Today there was the chance to observe a total lunar eclipse here at Lake Constance! Under a clear sky and at about 28°C after 10 o'clock in the evening the blood moon was perfectly visible. Right below the moon planet Mars was shining brightly. A lot of people were interested in seeing this phenomenon.

I recorded 2 pictures - one with the Fujifilm X-T1 and one with a Canon PowerShot SX710 HS. The zoom of this camera is extraordinary! With a small tripod and an exposure time of just 1 second I was able to get this result. Find the results of this evening below.

See this image in full resolution here.

This image is also available in full resolution here.