Author: Sébastien Aubry

You are looking at the starry sky from a planet that orbits around the sun at about 30 km per second. In addition, the Earth rotates on itself, making a complete rotation every 23 hours, 56 minutes and 4 seconds.
Therefore, depending on your location and the date and time of your observation, visible stars and constellations are not always the same. Their positions even keep changing during your observation.
In these circumstances, accurately pointing to a star (often invisible to the naked eye) with a telescope and following its movement to capture sharp images is a real technical challenge. A telescope must be set up in a rigorous and precise manner, taking into account the date and location information.

This time-lapse video shows the apparent movement of the stars caused by the Earth’s rotation. The position of the stars is permanently changing.

With a classical telescope, the setting-up procedure required to be fully operational and start capturing images of celestial objects can take between 30 minutes and 1 hour, even for an experienced amateur astronomer. With Stellina or Vespera, on the other hand, it only takes a few minutes and no particular technical skill.
Here is a detailed description of the setting-up and initialization process of the Vaonis observing stations and an explanation of why the process is easier and faster than with a conventional telescope.

1. Requirements for a successful initialization

1.1 External conditions

Apart from solar observations which require appropriate filters, initialization of the two telescopes for night observation requires a dark enough sky and visible stars. It is not necessary to wait for complete darkness. The observation stations can initialize from the nautical twilight when the sun goes down 6° below the horizon. However, the initialization duration of Stellina and Vespera can be shorter if it is a very dark night.
The sky must also be clear enough. In case of heavy cloud cover, initialization may fail. In any event, under these conditions, most observations are impossible.

As soon as enough stars are visible to the naked eye, you can launch the Stellina initialization. If it fails, wait for more darkness or check that the targeted region of the sky is clear.

1.2 Leveling the tripod

A similar step in setting-up Stellina and Vespera with a classic telescope is that it is required that the tripod be set horizontally. It is done manually by adjusting the length of each leg and checking the spirit level so that the bubble is positioned precisely in the center of the black circle.

Tip: Look at the spirit level from above to be sure of the position of the bubble. If you look at it from a different angle, you may think it is well centered while it’s actually not (due to the parallax).

Stellina’s bubble level allows the telescope to be set horizontally. This adjustment is required for more efficiency in pointing and tracking.

2. What is the initialization of a telescope?

2.1 Why is initialization necessary?

The start-up of Stellina and Vespera is much quicker than that of a classical telescope: less than 5 minutes in good conditions versus more than 1 hour for classical equipment. The main reason is that they are fewer manipulations to perform. Above all, one particularly long and complex step of the process with a classical telescope that is fully automatic with Stellina and Vespera is the syncing with the celestial sphere.

As explained previously, the appearance of the sky is constantly changing. Using a telescope to capture images of the universe requires accurate synchronization with the orientation and rotation of the sky. Time and geographical location must be taken into account. The mount axis must also be aligned in a particular way. Then the telescope can calculate the stars’ position and activate its motors to point and follow the lead to observe.

With Stellina and Vespera, sky syncing is achieved within 2 or 3 minutes by simply pressing a button.

2.2 Stellina / Vespera: automatic initialization with astrometric calibration

The initialization of Stellina and Vespera requires four main steps, which can be followed in the Stellinapp.

Step 1: Geolocation and time syncing

Firstly, to properly operate, the observation stations must be input with the time and the geographical position. This information is retrieved from the connected device you use to control the telescopes.
If Stellinapp indicates it can’t get the geographical coordinates of your observation place, your smartphone or tablet may not have an integrated GPS, or it could be disabled. You can input your geographical coordinates (longitude and latitude) manually if necessary.

Step 2: Astrometric calibration

Stellina and Vespera have to determine their orientation with respect to the starry sky position and the horizontal (although the horizontal alignment has been achieved manually with the spirit level, it may be necessary to improve it for further accuracy).

To achieve this, our stations use the astrometric calibration method, also known as “plate-solving” calibration. It consists of comparing the starfield captured by the telescope with an internal database to identify the targeted region of the sky:

1. The observation station targets a random area of the sky.
2. It captures an image of the bright stars.
3. The onboard computer analyzes the resulting image to determine patterns formed by groups of stars.
4. The patterns are compared with an internal database to find a match and determine the sky target region.

In case of a fail, the observing station starts over with another region of the sky. Most of the time, the second attempt is successful. Clouds or haze in the targeted region of the sky may be responsible for the failure.

Step 3: Tracking activation

To remain in sync with the sky, Stellina and Vespera must follow the apparent movement of the stars caused by the rotation of Earth. This is accomplished by continuously activating the motors on the two axes of the telescope (and a third axis on Stellina which also compensates the starfield rotation).

Step 4: Focusing

Focusing consists of adjusting the sharpness of the image generated by the telescope. It is achieved by adjusting the distance between the lens and the camera in order to view the stars as sharply as possible.
Successful focus allows one to get the maximum amount of detail on the images of galaxies and nebulae.

Stellina and Vespera have an integrated automatic focuser. To this day, it is the only astronomy consumer telescope in the world equipped with such a feature.
With conventional telescopes, focusing is done manually using various methods, such as using Bathinov or Hartman masks or checking star diffraction spikes, possibly with specific astronomy software. The observer is the final judge of the sharpness of the images (focus).

2.3 Classical telescope: polar alignment

Classical telescopes are often equipped with an equatorial mount (while Stellina and Vespera have an azimuthal mount). It facilitates star tracking, yet above all, it is required to capture images of the universe. When properly installed, the equatorial mount allows one to follow the apparent rotation of the sky by performing a slow and steady course on one of its axes. It is also required to keep the object’s orientation in the field of view (essential for astrophotography). Stellina and Vespera have a mechanism to compensate for the field rotation (optical for Stellina and software-based for Vespera) to get the same result as an equatorial mount.

To achieve the polar alignment, the observer must sequentially point to different stars. Depending on the accuracy of the result, he must manually apply corrections to the orientation of the polar mount axis.
Some mounts are equipped with a viewfinder built into the polar axis, allowing for a first approximate orientation by targeting the North Star.
On conventional telescopes, astrometric calibration does not apply as they do not have an integrated camera and an onboard computer system to operate.

3. Six tips to reduce initialization time or limit failure?

1. Regularly check to ensure that your Stellinapp mobile application and the internal program of the telescope are up to date. Visit the App Store or Google Play Store to check if new versions are available. You can subscribe to the Vaonis newsletter to be notified of updates and new features.
2. Set up the telescope’s tripod on a flat, stable, and non-slippery surface (avoid loose soil or sand). If the mount moves during your observation, the calibration will lose its effectiveness.
3. Shelter the telescope from the wind.
4. Level the tripod as carefully as possible with the spirit level.
5. Wait for sufficient darkness before starting the initialization.
6. Before starting the initialization of Stellina or Vespera, rotate the telescope’s body on its tripod (taking care not to move the tripod) towards a region of the sky free of obstructions, clouds, and stray light sources such as street lamps. The stars should be clearly visible in the chosen area.

During the observation, if you find that your telescope struggles to point to a new object accurately or that stars are oval-shaped rather than circular, you can solve the issue by restarting the initialization.

Image processing tutorial with Affinity Photo – Intermediate level

Did you know? You can now export the images of your observations in a 16-bit TIFF format. This raw file allows you to apply your own image processing settings and edit the images at your convenience. Doing so, you will get better image quality and personalize the results without the hassle from stacking files yourself on astrophotography software. This tutorial describes a method to process the images obtained from TIFF export using the Affinity Photo software. It explains basic concepts of image processing tools which can be applied using any other graphic design software.

For a more thorough understanding, please read:
Save, share and use STELLINA’s images

CONTENTS

1. Introduction
   1. Requirements
   2. About the technique used in this tutorial
   3. Tips for capturing better images with STELLINA
2. Processing steps
   1. Reveal the image
   2. Enhance the details
   3. Reduce the noise
   4. Adjust the colors
   5. Put the finishing touches
3. Can we proceed further?

Fig 1: The Orion Nebula. Left side: as shown on your screen when observing with STELLINA. Right side: after processing the image via the TIFF export.

Introduction

Requirements

Affinity Photo software

Affinity Photo is a raster graphics editor similar to Photoshop. It is able to export and read Photoshop files (.psd) but it is more accessible than Photoshop because of its price, and its interface is more user-friendly. It is available for Windows and macOS systems. A version for the iPad is also available.

Information and download: www.affinity.serif.com

Rate: about 50€/$50 (one-time purchase)

If you already own image processing software, it probably shares many features with Affinity Photo. So you should be able to draw inspiration from it.

The example file

This tutorial is based on an image of the famous Orion Nebula (M42).You can download the original TIFF file (as you would retrieve it during your observation) by clicking here..

The Orion Nebula is an interesting case study. It has a very bright center – its heart is lit by 4 stars forming a trapeze – with faint extensions. The challenge for any astrophotographer is to enhance the extensions without “burning” the heart.

About the technique used in this tutorial

There is no unique way to process an astronomical image. The vast array of software available on the market and their various functionalities offer many ways to achieve a result. There is also a multitude of possible results. If you process the same image several times with the same tools, you probably won’t get an identical end result. 

The method described here is one among many. For this tutorial, we’ve decided to use Affinity Photo, a versatile graphic design software accessible to all, rather than a dedicated astrophotography software.

Be aware that the settings required to process a particular celestial object may significantly differ depending on whether they are nebulae, galaxies or star clusters. Celestial objects can show very different characteristics, even within their category. The advantage of manual processing over STELLINA’s automatic processing is precisely to allow for the treatment of objects differently depending on their features. It is important to understand that this article is not about strictly following the step-by-step tutorial, but rather understanding the notions related to image processing and being able to apply the concepts to other cases.

This tutorial is organized into 5 main steps:

1. Revealing the image
2. Enhancing the details
3. Reducing noise
4. Adjusting colors
5. Adding the finishing touch

Tips for capturing your images with STELLINA

To obtain the best possible end image quality, you must begin with having all the right parameters in place when capturing photos with STELLINA. Here are a few tips that will positively impact your image’s final quality regardless of the processing technique you use.

• Set up your STELLINA outside about 1 hour before starting your observation. This will allow time for the optical and mechanical components to adapt to the ambient temperature, ensuring a more precise focus (sharp stars, less rejected images…). Stellinapp displays the temperature of the instrument. If you notice a significant drop in temperature, it’s likely your final image will show some defects.
• Target objects that are high in the sky, preferably above 30°. Close to the horizon line, the atmosphere absorbs more light. Furthermore, the more turbulence there is, the more the image quality will degrade. Keep in mind that during your observation, the apparent rotation of the sky will cause the celestial sphere to move. Use a star chart software such as Stellarium to control the height above the horizon of the object you plan to capture and check how it changes overnight.
• The longer, the better: plan for longer exposures.  Stellinapp provides minimum observation time recommendations for each target in order to get an image with decent quality. However, by prolonging the capture beyond the recommended time, you can achieve a higher quality result. We recommend that you to double the total exposure time (2 hours if we recommend 1 hour).
• The darker, the better: whenever possible, choose an observation site away from any artificial lights and use STELLINA when the moon is not too visible (new moon, waxing crescent phase…)
• Avoid setting up STELLINA on or near tarred, concrete or rocky surfaces. Those materials release heat at night, which increases the turbulence. Prefer grassy or earthy grounds.

Step 1: Reveal the image

At first glance, when opening it, the TIFF file may confuse you (see figure 2): the image appears almost completely dark. Actually, the signal does exist. What we can see at this point is basically the heart of the nebula with the 4 stars of the trapeze. This image refers to a 30 minutes capture. As mentioned in the tips above, we could have obtained an even sharper result with a 1 hour exposure.

The goal of this step is to expose the extensions of the nebula without burning its heart. While adjusting the settings, you will need to keep checking that the stars of the trapeze and the heart’s details remain distinctly visible.

fig. 2: the image as it appears in Affinity Photo while opening it, with the main interface’s elements.

Once you’ve opened the image with Affinity Photo, take a look at the panels on the right (figure 2). Make sure the” Layer Panel” is visible.

Like most graphics software, Affinity Photo uses a combination of layers that blend together to compose the final image. You can think of layers as being like sheets of paper that are stacked one on top of the other. Transparent areas of a layer reveal the layer below, while opaque parts of a layer obscure the layers below. Some layers may contain an image, while others are adjustment layers that affect all the visible layers below them. All layer management is carried out from the Layers Panel.

So far, we only have one layer with our image on it. To keep this source safe in case we need to start over, we will work on a copy of this layer.

• Click on the layer to select it, and in the “Layer” menu, choose “Duplicate“.
• The new layer appears in the panel. For better organization, let’s rename it “Tone Mapping” (you’ll soon understand why).

Activate the tone mapping mode: “Tone mapping persona” (see figure 2). Tone mapping is the equivalent of the HDR filter feature you can find in other photo editing software. This tool is particularly useful for images with a high dynamic range, which is the case with a 16-bit TIFF file.

Use the controls available on the right-side panel to apply the relevant settings (Figure 3).

• To adjust the overall brightness of the image, move the “Tone Compression” slider to low values, about 10%.
• To bring out the less bright parts of the nebula, increase the value of the “Local Contrast,” for example, to 30%.
• Slightly increase the “Blackpoint” value to darken the sky. During this step, don’t try to get an entirely dark sky background. You may lose details in the low lights. For example, set the slider to 3%.
• To protect the brightest areas from being burnt, activate the “Shadows and highlight” panel, and reduce the highlights to minus 100%.

You can try different settings to find a result that suits you best. Take care not to burn the heart of the nebula. If the stars of the trapeze are slightly burnt, we will be able to rectify this in the next steps.

These are the only settings to be made in the “Tone mapping persona“. Click on “Apply” (top left) to return to the standard mode.

fig 3: the interface of the “Tone mapping persona” with the settings to be made.

We now have an image that looks more like the Orion Nebula as we know it. By zooming in on the stars of the trapeze, we may notice that they are slightly burnt. In our primary image (which is still on the layer underneath), they were perfect. For this area only, we will try to let the underlying layer appear.

To achieve this, we will use the blend options (the goal of this feature is explained more in-depth in part 3).

• Make sure the “Tone Mapping” layer is selected.
• At the top of the Layer Panel, locate the gear icon “Blend Ranges” (see figure 2) and click on it to display the layer blending options.
• A new panel opens with two diagrams. Adjust the curve in the right-hand chart ((Underlying Composition Range))so that it looks like Figure 4. 

fig 4: setting the blending options for the “Tone Mapping” layer.

At this stage, the trapeze stars should no longer be burnt. We’ve revealed the underlying layer only for the very bright areas (where the stars in the trapeze are perfect).

This step is complete. The figure below compares the image at its opening in Affinity Photo with the result you should have at the end of step 1.

fig. 5: comparison before/after step 1

Step 2: Enhance the details

Now that we can clearly visualize the nebula, let’s try to enhance more details.

To achieve this, we are going to use a tool that looks intimidating at first glance, but is quite powerful: Tone Curves..  This adjustment is available as an adjustment layer.

• At the bottom of the Layer Panel, click on the “Adjustment” icon (see figure 2) then choose “Curves” in the drop-down menu.

A new layer is created, and the proper setting panel opens (figure 6 on the left).

fig 6: the tone curve, prior and post adjustments.

By clicking on the curve, you can change its shape in order to increase the brightness level of a particular tone range without impacting the other tone ranges too much.

In our case, we would like to increase the brightness of the dark tones without increasing the highlights in order to avoid burning the nebula’s heart.

• Click on the curve on the dark tone side to add a control point and then move it upwards to increase the brightness of this tone range.

As a result, we enhance the darker areas, but burn the very light ones. We therefore need to add another control point on the curve to retract the brightness of the highlights to their initial values.

• Add the required control points to the curve to get a shape similar to the one shown in Figure 5 on the right.
• Check that the details of the heart and the stars of the trapeze remain distinctly visible.

To complete this step, we are going to apply a detail enhancement filter.. Before proceeding, let’s flatten, i.e., merge, the layer containing our original image (called “Background” if you have not modified it) with the “Tone Mapping” layer.

• Uncheck the box next to the layer named “Curves setting” to temporarily disable the effect of this layer.
• Right-click on one of the other layers to bring up the layer contextual menu.
• In the contextual menu, choose “Merge visible“.

A new layer has been created. The initial layers are still available in case we need to go back to the previous steps.

• Ensure that the new layer is between the “Tone Mapping“layer and the “Curves Adjustment” layer.
• Activate the layer named “Curves adjustment” again by checking the relevant box.
• Rename the newly created layer “Clarity“.
• Make sure that the “Clarity” layer is selected, then in the menu “Filter / Sharpen…” choose the option “Clarity…“
• Adjust the intensity of the filter to increase the level of sharpness according to your preferences. Preserve the heart and stars of the trapeze. For example, you can set it to 40%.
• Click “Apply“.
• You can still adjust the tone curve settings if needed. This is the advantage of the adjustment layers: they produce non-destructive modifications and can be changed later.

This step is complete. The figure below compares the image between the beginning and the end of Step 2.

fig. 7: comparison before/after step 2

Step 3: Reduce the noise

When we zoom in on the image, we notice the presence of “noise.” Noise is the kind of granulation that appears, particularly in the darker areas of the picture.

The noise is distributed randomly and evenly throughout the image. It is less noticeable in bright areas as the brightness of the noise is low and therefore disappears in the strong “signal” of the bright areas.

When processing an image, the various adjustments performed to enhance the details may increase the image noise. Let’s see how to limit that noise, in order to preserve the image quality.

Please keep in mind that by reducing the noise too much, we could loose some of the smallest details. Therefore, it’s important to keep a balance and accept that a certain amount of noise will always be present.

• Duplicate the “Clarity“, layer to keep a back-up copy in case you want to revisit ((Layer menu / Duplicate)).
• Rename this new layer “Noise Reduction“.
• Make sure that the new layer is selected, then in the “Filters / Noise” menu, choose “denoise“.
• Zoom in on a faint area of the nebula that has details and where noise is more noticeable. Use the “Luminance” setting to find a suitable compromise between noise reduction and loss of details. For example, you can set the luminance slider to 20%.
• Click “Apply“.

Noise reduction has been applied to the whole image. We’ve seen that the noise was less noticeable in the bright areas. It would be interesting to apply the noise reduction only in the darker areas and then keep all the details in the bright areas.

You can achieve this by setting the blending options of the “Noise Reduction“layer. Indeed, we can indicate that the bright areas of the layer “Noise Reduction” become transparent. By doing so, the underlying layer “Clarity” which retains all the finest details, remains visible for that part of the image.

• Select the “Noise Reduction” layer.
• At the top of the Layer Panel, click on the gear icon “Blend Ranges“.

The Affinity Photo setting panel that opens shows two graphs that look like the tone curves we are now familiar with. They work similarly. Let’s pay attention to the diagram on the right “Underlying Composition Range“. It allows you to specify which tone ranges (black, dark, light, white) should become transparent (more or less) to show the underlying layers.

Like the tone curve graph, the left part of the diagram refers to dark tones and the right side to light tones. Our goal is to make the lighter parts transparent. Then the “Clarity” layer appears through only for the brighter areas, and the “Noise Reduction” layer remains visible on the darker areas where it is most useful.

• Click on the control point at the top right of the graph (the one that affects the white areas) and drag it downwards.
• Once at the bottom, slide it to the left as well. Watch the image to control how the noise varies to find the right setting.

The noise reduction layer no longer affects the highlights.

• To ensure the “Noise Reduction” layer affects all the darker areas, slightly move the control point at the top left of the curve (shadows) to the right.

The graph should look similar to the illustration below.

Fig 8. Blending options to be applied to the “Noise Reduction” layer.

This step is complete. The figure below compares the image between the beginning and end of Step 3.

Fig. 9 comparison before/after step 3.

Step 4: Adjust the colors

We have now reached the most creative step that will allow you to personalize your image with Affinity Photo.

So far, our Orion Nebula is quite pale compared to the images we are used to. Let’s enhance the colors and adjust them to get a look that suits us.

• Select the upper layer “Curves Adjustment“.
• Click the “Adjustments” icon at the bottom of the Layers panel and choose “Vibrance” from the drop-down menu to add a “Vibrance” adjustment layer.
• Move the “Vibrance” and “Saturation” sliders to their maximum values.
• Click on the “Adjustments” icon at the bottom of the Layers panel and choose “Selective Color” from the drop-down menu to add a “Selective Color“adjustment layer..

The “Selective Color” adjustment layer allows you to apply color changes to a specific hue. Since the Orion Nebula is mostly red, we will work mainly on this hue.

• In the Selective color setting panel, select “Red” from the top color drop-down menu.
• Set the “Cyan” slider to -100% (to remove cyan in red tones), the “Magenta” slider to +50%, and the “Yellow” slider to +100% to add each of these tones in proportion to the red tones.
• In the color menu, choose “Magenta” then set the sliders to “Magenta” and “Yellow” to + 100%.
• Eventually, in the Colors menu, choose black and place the “Black” slider at +5% to slightly darken the sky background and to add more contrast to the image.

At this point, the nebula appears quite pink, and we would like it to be more reddish. We can add a second “Selective Color” adjustment layer whose effects will cumulate with the first one.

• Click on the “Settings” icon at the bottom of the Layers palette and choose “Selective Color” from the drop-down menu to add a “Selective Color” adjustment layer.
• Select the color red from the menu and set the Cyan slider to -15%, Magenta to +35%, and Yellow to +100%.

The values given above for color correction are an example, and it is up to you to define how you want the nebula to look.

This step is complete. The figure below compares the image from the beginning and the end of step 4.

Fig. 10 comparison before/after step 4

Step 5: Put the finishing touches

Our nebula now looks very different from what it was on the smartphone or tablet display while we were observing with STELLINA: it is more detailed.

There are still some defects that we can try to eliminate or mitigate.

To begin with, the edges of the image show defects related to the capture. Let’s crop the image to remove the altered areas.

• Select the “Crop” tool from the left side toolbar (Figure 2), then adjust the frame and click on Apply.

he lower right corner of the image still shows a kind of unsightly halo. Let’s dim it by applying a dark gradient over it.

• Make sure that the top layer “Selective Color Adjustment,” is selected. At the bottom of the Layers panel, click on the “Add Pixel Layer” icon (see figure 2).

A new empty layer is added to the stack. Rename it “Gradient”.

• Select the “Gradient” layer.
• On the left toolbar, select the “gradient” tool (see figure 2).
• On the image, draw a short gradient from the lower right corner to the upper left corner at about 1/6th of the diagonal.

A control point is available at each extremity of the gradient to choose the color.

• Select the control handle on the bottom right corner of the image.
• Activate the “Color” panel in the right-hand setting panels and select the black color for this control point.
• Select the second control handle. Select the black color and a 0% opacity.
• Adjust the position of the second control point so that the gradient covers only the concerned area, without masking the wisps of the nebula.
• Now reduce the opacity of the “Gradient” layer to about 40%.

This step is complete. The figure below compares the image from the beginning and end of step 5

Fig. 11 comparison before/after step 5

Should we go further?

We can now consider that the processing of the Orion Nebula image from STELLINA’s 16-bit TIFF export on Affinity Photo is complete. We have managed to get a more detailed image, with colors that are quite natural. We have also preserved the heart of the nebula, which highlights many details.

When it comes to image processing, the users can be tempted to go further to see more colors, more details, accentuate further details and colors. How do you know when you should stop?

There are no laws or rules regarding image processing. However, a good indicator that the image processing is sufficient is that the image looks natural. Further processing will result in the details being more detailed. Yet, the result may not look natural even to the untrained eye. Furthermore, too much image processing may accentuate the defects in the image.
Experimenting and comparing your results with others is the key to learn how far you can go.

To end this tutorial, here is a way to improve the image a bit more while keeping the ability to balance this improvement in case you have regrets (and without having to start the processing over again).

• Temporarily disable the “Gradient” layer.
• Right-click on one of the layers to select the contextual menu and choose “Merge visible“.
• Place the newly created layer between the “Gradient” layer and the “Selective Color adjustment” layer.
• Select the new layer and rename it “Extra peps“.

We are going to use the tone mapping persona again to enhance the details on this layer.

• In the top toolbar, click on “Tone mapping persona“.
• Set the tone compression to 0% and the local contrast to about 20%.
• Click “Apply“.
• Activate the “Gradient” layer again..

By doing so, we have just created a layer of the image with enhanced sharpness. But we have also accentuated the defects.

To balance the effect, we can adjust the opacity of this layer to more or less blend with the underlying layers.

We can also set the blending options for this layer to affect only the highlights of the image where the details actually are and preserve the dark areas where defects are more easily visible. Proceed in the same way as you did with the “Noise Reduction” layer by adjusting the blend ranges.

Here is what the curve might look like:

fig.12: blending option settings for the “Extra peps” layer

Congratulations, you’ve reached the end of this tutorial! Don’t forget that each celestial object is different and will require custom settings. The more time you spend on Affinity Photo, the more experienced you will become and you will see progress. Ask for feedback from fellow amateur astrophotographers.  

Please share the results of your work on social networks and in the #myStellina Facebook group.

• To save your Affinity Photo working file, choose “Save As” from the file menu.
• To export your image for sharing, select “Export” from the file menu.

You can download the Affinity Photo file (NB: the photo is in low resolution) used in this tutorial by clicking here..

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

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.

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.

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.

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.

In a nutshell: