Whether you are a beginner excited to share your exploration of the universe or a more experienced and demanding amateur astronomer, STELLINA‘s got you covered and can satisfy everyone’s expectations.
Three methods are available to save, share, and edit the results of your observations.

ABSTRACT
1. JPEG for instant results: save or share what you see on your screen
2. TIFF for manual image processing: raw images that you can edit by yourself
3. FITS for astrophotography experts: stack and process raw images yourself

 

Carina nebula captured with #myStellina

The Carina Nebula captured with STELLINA. Image processed from the exported file in 16-bit TIFF. Image credit: Sébastien Aubry

For a better understanding

STELLINA runs a real-time image stacking process. While you are observing a celestial body, STELLINA keeps capturing new images and adds them to a “stack” to build up the final image you are visualizing. This is a commonly used process in astrophotography. Its goal is to improve the quality of the final rendering by reducing noise (a spurious signal generated by the electronics of any sensor that is randomly distributed over the image) and by highlighting the faint areas. For this reason, the longer you observe, the more the image quality improves, as shown in the video below.

 

fig.1: As your observation keeps progressing, STELLINA improves the image quality in real-time.

In this article, we will call each individual image that is captured and stacked together a “frame”.

Other than the very first image displayed when STELLINA starts capturing, you can’t see the unstacked single frames, but only the image built up from all the pictures that have been added to the previous stack. However, it is possible to retrieve all the single frames for a specific use, as you will see later.

Each single frame refers to an exposure of ten seconds. When STELLINA recommends an observation time of 30 minutes (1800 seconds), this means you will have to collect 180 ten-seconds exposures (1800 divided by 10).

Note: The Moon, the planets, and the stars available via the Stellinapp object index are displayed live. There is no stacking done on these objects.

1. JPEG for instant results: save or share what you see on your screen

Overview

The image displayed on your smartphone or tablet is the result of the stacking process carried out by STELLINA’s software in real-time. Our image processing algorithms automatically improves image quality and help enhance the details.

How to save the file?

Click on the “Image” icon on the top right corner of the Capture tab. You will get several options (figure 2).

fig. 2: The Image menu and its export options

fig. 2: The Image menu and its export options

You can:

  • Share STELLINA images currently displayed right on social networks,
  • Save the image in Stellinapp,
  • Save the image into your mobile device’s photo album.

If you plan to edit or share the image later, we recommend that you save your photo in your device.

You can save STELLINA images at any time during your observation. You can also automatically save all generated images by plugging a USB memory stick into the battery compartment prior to beginning your observation. STELLINA will detect your USB stick and will ask you to choose the image format you would like to save (figure 3). Choose the “JPEG” format.

Fig. 3: STELLINA Saving Options on a USB stick.

Fig. 3: STELLINA Saving options on a USB stick.

How to use the file?

After your observation, you may be tempted to edit your image to improve the colors or try to bring out more details. Actually, as soon as the image is saved, Stellinapp will offer you some basic settings to adjust the image to your needs.

In case you want to edit the image in a graphics software, please note that the actions you can perform are limited and may degrade the image quality. There are several reasons for this:

  • STELLINA’s jpeg images have already been processed.
  • STELLINA images are saved in JPEG format: in order to reduce the weight of this well-known format, a digital digital compression is applied. This compression leads to barely perceptible changes to the pixels of the image. Running a deep processing on a JPEG image will bring out those imperfections (sometimes called “compression artifacts”) and eventually degrade the image quality (Figure 4).

In order to get a better image than what you see on the screen, STELLINA offers a second format you can use to pursue manual image processing: TIFF files.

Artifacts caused by JPEG compression

Fig. 4: Zooming in on the detail of an image. On the left: raw image – On the right: JPEG compression where artifacts appear (for example, around the stars).

2. TIFF for manual image processing: raw images you can edit by yourself

Overview

While you are observing, STELLINA automatically processes the captured images to provide you with bright, high-contrast, and detailed rendering.
However, the celestial objects you can observe, whether they are star clusters, galaxies or nebulae, have different features: they are more or less bright, more or less contrasted, with variable colors and show fields more or less dense with stars.

As STELLINA applies automatic processing on the images, it is not possible to handle each object’s specific feature. However, it is often possible to get better quality images by running out the image processing by yourself. This requires some learning and time, but the experience is fun, and the results can be very satisfying.

Figure 5 – Comparison between the image displayed on the screen and the result of TIF export processing.

As stated above, the images saved with the previous method can only be slightly improved. Stellinapp offers you an alternative option: the ability to export the image of your observation in a format suitable for advanced image processing: the 16-bit TIFF.

Note: This format is not available for the Moon, planets and stars available via the Stellinapp object’s index.

How to save the file?

To activate this option, you must first enable it in the app. Go to Profile > Gear icon > Settings > Enable TIFF export (figure 6).

You’ll now see the TIFF export option when clicking on the Image icon in your Capture tab during an observation.

If a USB drive is connected to STELLINA, the TIFF files will be saved in your USB drive but this operation, unlike FITS files, is not automatic. You still need to click on “TIFF export” during the observation. Alternatively, you can save it in the photo album or a folder of your mobile device, transfer it directly to your computer or send it via email if you have an Internet connection.

fig. 6 : TIFF export options in STELLINA settings.

fig. 6 : TIFF export options in STELLINA settings.

How to use the file?

The TIFF export allows you to retrieve an image which is the equivalent of a RAW file for a DSLR camera. STELLINA will automatically stack the single frames, but its image processing algorithm won’t apply and the image will remain untouched. It is raw data. The image is not compressed; therefore, the file size is more significant. It also has a higher dynamic range (number of different shades that can be rendered): 16 bits versus 8 bits for a JPEG file.

The TIFF file can be edited with any graphic design softwares such as Photoshop, Gimp, Affinity Photo, Luminar. You can also use this type of file with astrophotography dedicated software such as PixInsight.

3. FITS for astrophotography experts: stack and process raw images yourself

Overview

The STELLINA images retrieved with the previous methods are a result from the automatic stacking process performed by STELLINA in real-time during an observation.

It is possible to automatically save each single frame that builds up the stack. The purpose of this method is to manually stack the unit images by yourself to have better control over the process. This action can be performed with software dedicated to astronomical image processing such as Deep Sky Stacker.

The automatic stacking performed by STELLINA is elaborated. For example, it rejects single frames which do not comply with the required quality (tracking issues, wind, vibrations…). When it comes to saving the FITS files, the rejected frames will also be saved, allowing the users the option of using them or not.

Yet, processing the FITS files manually requires much experience and good knowledge of astrophotography. If the manual stacking is not correctly done, the final image may have a lower quality than the TIFF export made by STELLINA. Besides, it takes several hours to process.

How to save the file?

To retrieve the FITS files, you must connect a USB drive to one of the slots located in the battery compartment before starting your observation. STELLINA will detect your USB key and ask you to choose the image format you wish to save. Choose the “FITS” format.

The automatic saving of FITS unit images can generate a huge amount of data. If you plan to capture several celestial objects in one night or to make very long exposures, we recommend you purchase a USB drive with at least 32 GB.

Note: This format is not available for the Moon, planets and stars available via the Stellinapp object’s index.

How to use the file?

The FITS format is widely used in amateur astronomy, as well as in the scientific field in general. Its distinctive feature is to be able to store “visual” as well as other information. However, this type of file is not usually supported by standard graphic design software and can only be opened with specific astrophotography software.

About “dark files”

During the manual stacking process, astrophotographers commonly generate images called “darks” in addition to images of the star itself. Darks are pictures taken while the telescope aperture is obstructed so that no light can reach the sensor. One would expect to get a completely black image (hence the name “dark”). Actually, this type of image contains a weak signal generated by defects of the sensor. For example, it can be hot pixels. The signal of the “darks” is subtracted from the images of the celestial body. Proceeding this way removes the glitches generated by the sensor on the final image.

Does STELLINA take darks?
During your observation, STELLINA does not generate darks, so you won’t find this type of file on the USB key. When STELLINA automatically applies its algorithms, it uses a predefined dark pattern that characterizes the sensor’s spurious signals and does other corrections through various processes.
If you wish to use “dark” images in your manual stacking process, you will have to capture them by yourself. To do so, start the observation with STELLINA, then put an opaque cover in front of the lens (no light should be able to reach the sensor). The display on the screen of your smartphone or tablet will show no evolution of the image, yet the corresponding FITS files will be saved on the USB key.

In a nutshell:

JPEG TIFF FITS
Audience All Intermediate Expert
Processing Automatic by STELLINA Manual, to be done Manual, to be done
Stacking Automatic by STELLINA Automatic by STELLINA Manual, to be done
Compression Yes (destructive) No No
File size About 1 Mb About 10 Mb about 13 Mb / single frame
Image size 1500 x 990 1500 x 990 3096 x 2080 (6,4 Mp)
Backup Smartphone, tablet, USB stick Smartphone, tablet, computer, USB stick USB drive
Softwares Any photo editing software Photoshop, Affinity Photo, Luminar … DeepSkyStacker, Registax, PixInsight, SIRIL, IRIS …