Image Processing Overview: Data Reduction

This post describes how one creates an astro-image like the one below. This will be a bit of a dry post. Let’s start start with the finished product, an image I took of Messier 81 in the constellation of Ursa Major, also known as Bode’s Galaxy.

Messier 81

I use the term “image” intentionally to contrast with “photo.” These images are the result of capturing data on a CCD through a telescope in multiple long exposures. They are not photos. These data need to be processed to become the pretty images we see. The image of M81 above used 3 hours 25 minutes of exposure time, taken in multiple 5-minute exposures with white light, red, green, and blue taken separately and processed as described below to create the final image.

The data are noisy. There are anomalies in the optical system like dust or uneven illumination though the telescope. Heat causes random charges to accumulate on a CCD during long exposures, even with the CCD chilled to -25°C. The CCD chip itself may have minor defects that generate differences in how photons are collected. The electronics introduce noise when data are read off the CCD and passed to the computer controlling the camera. Finally, the objects being imaged are very dim, so the signal we are trying to capture is small, just barely above the background glow of the sky.

Continue reading

Andromeda Galaxy, Orion, the Pleiades, and the Double Cluster

Over the Thanksgiving weekend, I was able to get the iOptron Sky Tracker Pro out again and try some more wide field astrophotography. I learned (and should have known) that level is as important as polar alignment for good tracking. Having done most of my imaging with autoguiding which corrects for leveling and other mechanical errors, I did not level properly back in October and had a number of disappointing images. This night, however, turned out better.

I used my Sony RX-100 M4 camera to take the images, controlling the camera over WiFi using Sony’s PlayMemories Mobile software. This software allows complete control of the camera’s function from any iOS or Android device and is available from the respective app stores. [Please note that I am currently an employee of Sony Pictures Entertainment, and Sony is the parent company of my employer.] This night, I used my iPad. I selected three targets: The Pleiades and the Double Cluster in Perseus, M31 — the galaxy in Andromeda, and the constellation Orion.

For each image, I used 15 second framing exposures. Focus was set to manual and at infinity. Once framed, I took longer images, settling on three minutes for my target exposure time. The camera performs a long-exposure noise reduction that lasts as long as the exposure. So a three minute exposure is six minutes of imaging time. I tried turning that off in my failed October attempt, but the remnant noise was not easily removed (I admit I have not experimented extensively with this, but I did get good results with camera long-exposure noise reduction turned on).

I captured all the images in Sony raw (.arw) format and imported them into Adobe Lightroom. I exported them in TIFF format and then processed them in PixInsight. In PixInsight, I performed background neutralization, color correction and balance, and some contrast adjustment. I imported the result back into Lightroom, did light touch-up and noise reduction to produce the final results.

The first image I took was of the Pleiades and the Double Cluster in Perseus. Two beautiful objects in a small telescope or with binoculars. This was a simple, three minute exposure. The Pleiades are on the right in the middle of the image, the Double Cluster is in the upper left, and the bright star in the lower left is Capella.

Please click on any of the images to be taken to the gallery and see a higher resolution image.

The Pleiades and the Double Cluster

For my image of the Andromeda Galaxy, I did a bit more processing. I took one two minute exposure and a one minute exposure, combining them in PixInsight. I would have taken a three minute single exposure but it was cold and I wanted to get on to Orion. This image had the most processing in PixInsight. The galaxy is the fuzzy spot in the middle of the image.

The Galaxy in Andromeda

The final image I took was of Orion, which was fairly low in the sky, not more than 40° above the horizon. I also zoomed the camera which reduced the f-ratio by one stop, from 1.4 to 2.4. Because of this, I took a four minute exposure. My only comment on the processing is that I think I may have clipped the blacks too much. I’ll try again when it is higher in the sky.

You can see the Nebula in Orion in the center right. Note that the two brightest stars are Betelgeuse and Rigel. Rigel is on the left, for you should always remember that Rigel is not red. If you zoom in to the lowest star in Orion’s belt (Alnitak) you can see a little red which is the Flame Nebula. I have an image of it in the gallery.

The Constellation Orion

Comments are welcome and I hope you enjoy the images.

Wide Field Astrophotos

Since I haven’t taken the time to get the observatory up and running for quite a while, I have instead done some night photography with my Sony RX100. To that end, I acquired an iOptron Sky Tracker Pro tracking camera mount. It is a great device, complete with polar alignment scope and internal battery.

I took two nice Milky Way shots on my first night imaging on September 4th. The first shot is looking directly overhead. The bright star toward the top of the image is Vega, Deneb is near the mid point on the left, and Altair on the right. This is one three-minute exposure processed in Adobe Lightroom. (Lightroom is an absolutely amazing product.)

The Milky Way

The second shot is in the south, with the galactic center in the middle of the frame. The three bright stars on the mid-right of the image are actually two planets and a star. Saturn is on the top, Mars on the left, and Antares under Saturn. This is also one three-minute exposure processed in Lightroom, with some obstruction removal in Photoshop.

The Central Milky Way

Click on the images to be taken to the detail page in my photo gallery.

Moon, Venus, and Mercury Conjunction

Back in early February, we had an interesting time from a planetary observation standpoint. All of the naked eye visible planets can be seen in the sky in the early morning. Jupiter is in the west, moving east we have Mars, Saturn, Venus and Mercury. On February 6, 1016, there was an old sliver the Moon that joined Venus and Mercury. I was able to get up early and get some images of that conjunction event.

I was a totally clear morning. A little chilly at 40 degrees F with a fairly strong 10-15 mile an hour wind from the east. It was bracing and beautiful. The first shot is a close look a the three objects, the second a wider view of the Anza valley with Santa Rosa Mountain and Toro Peak on the left.

Venus on the right, Mercury on the bottom, and the Moon at the top left.

Venus on the right, Mercury on the bottom, and the Moon at the top left.

Conjunction Wide

Conjunction Wide

Moon Events Calendar File

I like to have the dates and times of the phases of the Moon in my calendar. Years ago, I found a site that provided a vCalendar format file that I could import into Outlook. Unfortunately, the data from that site ended on December 31, 2015.

Fortunately for you, I can provide an update. For those who just want the vCalendar file, you can download Moon-Events-2016-2017.vcs. That file contains calendar entries for all the Moon Phases in 2016 and 2017 and can be uploaded into Outlook with the following steps (this is from Outlook 2016 / Office 365):

  1. Go to File > Open & Export > Import/Export
  2. Select “Import from an iCalendar (.ics) or vCalendar (.vcs)” and click “Next”
  3. Change the file type in the Open dialog to “vCalendar format (.vcs)”
  4. Navigate to where you saved Moon-Events-2016-2017.vcs, select the file, and click “Open”
  5. Select “Import” to import the calendar entries into your calendar

Now I will describe how I made the vCalendar file. I first went to the United States Naval Observatory website, specifically to the Phases of the Moon page from the Astronomical Applications Department. From the Moon Phase page, you can generate up to 99 Moon events which are displayed in your browser.

I took that text and pasted it into a spreadsheet. Using Excel text functions I parsed the data so I could build up the required vCalendar syntax. That meant changing the text from the USNO:

Last Quarter 2016 Jan 02 05:30

Into the required syntax for a vCalendar entry:

BEGIN:VEVENT
DSTART:20160102T053000Z
DTEND:20160102T053000Z
SUMMARY;ENCODING=QUOTED-PRINTABLE:Last Quarter
PRIORITY:3
END:VEVENT

Each of those went into a text file and I added a header:

BEGIN:VCALENDAR
PRODID:-//Aschlei//MoonEvents//EN
VERSION:1.0

And a footer:

END:VCALENDAR

I then saved the text file with a .vcs extension and I was able to import the events into Outlook. You can import it into other calendars like Google calendar, but they come with Moon events built in so it generally isn’t necessary.

You can download the Excel file I used with the text parsing and concatenation, Moon-Events-2016-2017.xlsx, if you’d like to try it yourself. I’ll probably download it in late 2017 when I need some more Moon events.

I hope you found this useful.

Astronomy Goals

I haven’t had much time or focus on astronomy for, really, the past year. Many reasons. So in this post I will set forth my astronomy goals for the year ahead.

  • Install and image with the new camera
  • Take many solar images with the Lunt scope
  • Image Saturn
  • Start setting up the original Observatorio de la Ballona for narrowband imaging with the ST-10

And so, there it is.

Some Astronomy Progress

It has been a fairly crazy couple of months for me and all the others at my company. And there is much work ahead. This work led to missing a month’s post: There was no post for December 2014. But I won’t miss January 2015.

Over the last two weekends, I actually made some progress with upgrades to the observatory. First of all, it got a thorough cleaning. A movable roof does not seal tightly, so there was plenty of red Anza dust everywhere. It is now in tip top shape. Birds occupying the roof motor housing prevented any observing that first weekend of work. I was able to put the self guiding filter wheel on my new SBIG STXL-6303E camera. A step forward!

On the long Martin Luther King Jr. weekend, I was able to test out the current set up. Everything worked fine even if I was forced to shut down early due to high winds. I also installed the filters (Astrodon LRGB, Ha, SII, and OIII). And I connected the camera to a computer and it worked.

The real tests are ahead, when I rebuild the setup of the last two years and get it tuned for easy use. That is many weekends of work. I am looking forward to it.

Changes at SBIG

This is old news, but I feel compelled to mention it.

Back on October 1, 2014, Diffraction Limited, creators of Maxim DL, acquired Santa Barbara Instruments Group (SBIG).

Diffraction Limited, a company well-known for its Cyanogen brand astronomy products, including MaxIm DL imaging software, today announced the acquisition of the assets of Santa Barbara Instrument Group Camera Division of Aplegen, Inc. As part of this acquisition, Diffraction Limited is assuming all responsibility for manufacturing, product development, customer service, repair and warranty support.

Several years ago, SBIG was acquired by Aplegen, Inc,. a medical imaging company. I figured this was a way for the founders to get some of their money out of the company and a basis for continued growth. SBIG has continued to produce good products and new innovations.

I am hopeful that this new change in ownership is a good thing. Doug George, owner of Diffraction Limited, is a good guy. I’ve met him several times at the AIC in San Jose. Others I have communicated with believe this is a good thing for the company. And that is good for imaging, because SBIG consistently has set the standard for astronomical cameras.

Sun Images with New Solar Scope

A few weeks back I acquired a new, dedicated solar telescope. It is a Lunt LS80 THa with the double stack module. I admit that I was attracted to solar scopes by the Coronado line of telescopes, purchased sometime back by Meade. Upon doing my research, I learned that the Lunt line is made by the founder of Coronado and manufactured in the United States. I purchased from Anacortes Wild Bird and Telescope, a fine establishment with an excellent staff.

Of course I wanted to take images. My first attempt was not worth posting outside of Facebook. And when I tried again, I had more follies with video format. For all programs, RGB24 is a large file, but a good, uncompressed format. And it works.

For this effort I acquired a new camera off of Astromart. It is am Imaging Source DFK 31AU03. It has a 1024×768 CCD, and worked very well for what I wanted to do.

I processed the 2,000 frame videos in Registax, AstroStakkert, and AviStack. AviStack was the slowest, but it produced the best result, based on visual assessment. I am sure all of these programs are good, and I am a beginner on all but Registax. From there, I moved to PixInsight. I only aligned and stacked the images in these programs. All real enhancement was done in PixInsight.

In PixInsight, the real enhancer was deconvolution. I used modified Lucy-Richardson with a combination of 3.0 and 3.5 StDev PSF, with 200 iterations. More the better I always say. Before deconvolution, I doubled the pixel size of the image. I did use HDR transform to add some contrast, but I weighted the deconvolved image more using pixel math. I am happy with the results. Some minor finishing was done in Photoshop.

Here is the first image. I stretched out the image with a mask to show the prominences on the rim of the Sun. It did tweak part of the limb, but I think it looks good.

The Sun

On the second image, I tweaked the color in Photoshop to brighten it up a bit. I think it reveals the details of the Sun better.

The Sun