Keith's Image Stacker is an image processing program that is oriented primarily toward astrophotography. Keith's Image Stacker for Mac. Or a series of long exposures of a deep-sky object. The latest 64-bit version seems very stable. More recently, two new stacking programs have become available; Starry Landscape Stacker (£38.99) and Sequator (free, but a contribution by paypal for a cup of coffee or two is suggested). The former is only available for the Mac and the latter for Windows. They both have the ability to treat the sky and any foreground separately – great for wide angle night landscapes. DeepSkyStacker is a freeware for astrophotographers that simplifies all the pre-processing steps of deep sky pictures. Simple post-stacking processes to quickly view the final result. Saving the resulting image to a TIFF or FITS file (16 or 32 bit).

Astrophotography is closer to science than art, and there is no such thing as “getting it right in camera.” This means you cannot simply point the camera at the sky and snap away.

In astrophotography you cannot avoid post processing your images, so stacking and editing your images serves three main purposes:

1. Reduce noise and deal with light gradients and vignetting.
2. Improve signal to noise ratio.
3. Reveal the faint details in the image.

Image stacking is the technique used to improve the signal to noise ratio, and it is the only noise reduction method that will boost the image details rather than smear them out.

In this article, we will discuss some of the most popular software available for astrophotography image stacking.

Note: Don’t miss the detailed video at the end of this article, It was created to help show you how to quickly start using some of the stacking software mentioned in this article.
Click here to skip to our Image Stacking Demo Video.

What Does Stacking Photos Mean?

The concept behind image stacking is simple, but to appreciate how it works, there are a couple of things we have to consider:

1. A stack can be visualized as a pile of images all stacked one on top of the other;
2. Each digital image is formed by a set of pixels, all having a certain value: dark pixels will have a lower value than the bright ones;

In the simplest form of image stacking, the pixels values for all images in the stack are averaged to produce a single image.

What is the purpose of stacking photos?

The result is a single image with improved signal to noise ratio, i.e., with better details and lower (random) digital noise and better details.

The scheme below illustrates the concept.

If the considered digital noise affects the pixel values randomly across the stack, then the result of averaging the stack is that the random component of the noise to the pixel value is significantly reduced.

ISO noise and Luminance noise and Chrominancenoise are examples of digital noises that are random.

The image below shows a real-life example from stacking 30 images from my Sony RX10 bridge camera taken at ISO 6400. As you can see, the original images showed a greater deal of noise (grain) than the stacked one.

The More Images You Stack, The Better

The more images you stack, the cleaner the resulting images are, as shown in the comparison below.

While Image stacking creates a cleaner image, it often softens the image: digital sharpening techniques are then used to recover sharp looking details.

Finally, bear in mind that the progression of image quality is not linear.

If stacking 4 images improves the image quality of 50% respect what you got by stacking only 2 images, to improve a further 50% the image quality from stacking 50 images, you may need to stack 300 images or more.

Image Stacking And Movement

If nothing moves between shots, like in the previous real life example, implementing image stacking is very simple: just group the images and average them to smooth out the noise.

With a moving subject, grouping and averaging the images will not only smooth out the noise, but also the subject itself.

This is the same principle for which long exposures of passing traffic and crowd result in a street image without cars nor people.

This effect is amplified with the number of images used, and the moving subject could simply disappear from the stacked image.

To resolve the issue, you have to align the images based on their content before stacking.

Due to image alignment, you may have to trim the edges of the stacked image to get rid of artifacts, but your target will not be lost.

Note that while in theory you can stack images of a static scene taken with the camera on a tripod, in reality, those images will probably differ at the pixel scale due to micro-movements. It is always beneficial to align the images before stacking.

How To Shoot For Exposure Stacking Your Images

Image stacking can be done with any camera and even camera phones and with images in both RAW and JPEG format.

Nonetheless, some things can be done to improve the final result:

1. Lock the focus, so that the camera will not hunt for it between images. This will also help to keep the focus consistent through the shooting sequence.
2. Keep the same settings, in particular shutter speed, aperture, and focal length: you don’t want to change the camera field of view during the sequence, nor the brightness of the images or the depth of field.
3. If you are shooting on a tripod, disable image stabilization. If you want to shoot handheld, do so only for short sequences at very high shutter speed.

Free Programs For Mac Downloads

Image Stacking In Astrophotography

Related:Astrophotography Software & Tools Resource List

As said previously, image stacking is a standard technique implemented in any astrophotography editing workflow for,

1. A star field from a fixed tripod.
2. A deep sky object from a tracking mount.
3. The Moon handheld.
4. A starry landscape from a fixed tripod or tracking mount.

Every astronomy image will benefit from image stacking.

List Of Photo Stacking Software For Astrophotography

Here is a list of software used in astrophotography for image stacking.

Adobe Photoshop

Complete Image Editor | Commercial – Subscription Plan Photography Bundle $9.99 / Month | Mac OS X, Windows

Pro

• Versatile
• Available for Mac and Windows
• In bundle with Adobe Lightroom CC, Bridge, Camera Raw, and web space
• Many action packs and plugins available for astrophotography

Cons

• Subscription Plan only
• Can’t be used to calibrate light frames
• Stacking capabilities are somehow limited

If you are interested in photography, chances are you know Adobe Photoshop is the standard in the industry and does not need introductions.

With Adobe implementing a subscription plan for their applications, if you are using Lightroom CC for your everyday photography, your plan subscription will also include Photoshop CC and Bridge CC.

And for astrophotography, Photoshop is what you need. Lightroom cannot stack your images nor perform the histogram stretching, two crucial steps in the editing workflow for astrophotography.

In this article, we have already covered in detail how to stack astrophotography images with Photoshop.

Sequator

Deep Sky And Starry Landscape Stacker | Freeware | Windows

Pro

• Free
• Easy to use
• Fast
• Suitable for both Starry Landscapes and Deep Sky images
• Can create Star Trails

Cons

• Windows only
• Limited set of options
• Not suitable for Planetary astrophotography

Sequator is an easy-to-use and intuitive astrophotography software for stacking both starry landscape and deep-sky images. It can also be used to create star trails.

While not as advanced as other stackers, it nonetheless allows you to calibrate your light frames with dark and flat calibration frames. It also allows you to remove light pollution, reduce noise, and perform other simple tasks on the stacked image.

Starry Landscape Stacker

Starry Landscape Stacker | Commercial, $39.99 | Mac OS X

Pro

• Fast
• Easy to use

Cons

• Mac Os X only
• Does not read RAW files

If you are into starry landscapes and you are a Mac user, Starry Landscape Stacker is a must-have.

Easy to use, it allows you to stack and align the sky and the foreground independently by letting you easily mask the sky.

Unfortunately, the software lacks the support for RAW formats, thus forcing you to convert your RAW images in the more heavy TIFF format.

Aside from that, it works very fast and the final image is of good quality. You can also save the sky only, which is useful to further edit the shot in Photoshop or similar editors.

Starry Sky Stacker

Deep Sky Stacker | Commercial, $24.99 | Mac OS X

Pro

• Fast
• Easy to use

Cons

• Mac Os X only
• Does not read RAW files
• Basic

Starry Sky Stacker is Starry Landscape Stacker brother and it has been created to stack deep sky astrophotography images.

As Starry Landscape Stacker, Starry Sky Stacker is very easy to use and intuitive, although very basic.

If you are a casual star shooter and a Mac user, this could be a good choice for you.

Deep Sky Stacker

Deep Sky Stacker | Freeware | Windows

Pro

• Free
• Easy to use
• Fast
• Full light frames calibration
• Features Comet stack modes
• Can Drizzle
• Many advanced stack options and methods available

Cons

• Windows only
• Post-processing is quite limited
• Not suitable for Starry Landscapes nor for Planetary astrophotography

Deep Sky Stacker, better known as DSS, is arguably one of the most widely used software to calibrate and stack astrophotography images.

With DSS, you can fully calibrate your images with Darks, Flats, Dark Flats, and Bias calibration frames for the best results possible. Light frames are analyzed and scored by quality so that you can decide which percentage of best images you can stack (Best 75% by default).

A very interesting feature is that with DSS, you can easily combine images taken during different imaging sessions, to produce images of higher quality.

Autostakkert!

Planetary Stacker | Freeware | Windows

Pro

• Free
• Easy to use
• Suitable for Planetary, Lunar and Solar images
• Stack full planetary disk and lunar surface close-ups

Cons

• Interface a bit confused
• It does not offer wavelet sharpening
• Windows only

Autostakkert!, also known as AS!, is a very popular free software among the solar system astrophotographers. With AS! it is easy to stack both images showing the full Planetary (or Lunar or Solar) disc and images showing lunar surface close-ups.

The interface is a bit confusing, particularly in the beginning, but it is easy to navigate through the different steps for the stacking.

Unfortunately, AS! does not offer wavelet sharpening, which is a widely used technique in planetary and lunar astrophotography. For this, you can load your stacked image in Registax, another freeware software for Windows only that, sadly, is now “abandoned-ware.”

Lynkeos

Planetary Stacker | Freeware | Mac OS X

Pro

• Free
• Has deconvolution and wavelet sharpening
• It is probably the only freeware planetary stacker for Mac OS X

Cons

• Not very intuitive
• Somewhat slower than Autostakkert!

Lynkeos is perhaps the only freeware planetary stacker software for Mac OS X, sparing you from turning to Windows for using Autostakkert!.

The interface is quite intuitive to navigate, but not when it comes to performing the different tasks.

Deep Sky Stacking Programs For Mac Download

On the other hand, it offers a deconvolution method and wavelet sharpening, a must-have for a planetary stacker. Definitely worth having a look at it if you are a Mac user.

SiriL

Deep Sky Astrophotography Editor | Freeware | Mac OS X, Windows, Linux

Pro

• Free
• Cross-Platform
• Active development

Cons

• A bit convoluted and not as intuitive as other stackers

SiriL is a freeware, cross-platform, astrophotography package that will let you calibrate, stack, and develop deep sky astrophotography images.

While not as easy and intuitive as Sequator or DSS, it offers a lot of options and produces good results. There is an active community, and it is under constant development.

Astro Pixel Processor

Deep Sky Astrophotography Editor | Commercial $60/Yr Renter License Or $150 Owner License | Mac OS X, Windows, Linux

Pro

• Full-grown astrophotography package
• Fairly easy to use
• Mosaics are created with ease and are of great quality
• Active and constant development
• Cross-Platform
• 30-days Trial period
• Affordable yearly subscription

Cons

• Only for deep sky astrophotography
• No Comet stacking mode

With Astro Pixel Processor (APP), you step in the realm of full-grown astrophotography packages, with many advanced options and methods to calibrate, stack, and post-process your deep-sky images.

Compared to PixInsight (PI), the software benchmark for the category, APP is cheaper and way easier to use, which makes it one of the best PI alternatives.

If you decide to buy it, you can choose between the renter’s license for $60/yr, to always get the latest version of APP, or the owner’s license for $150, but you will have to purchase the license again for major update releases.

PixInsight

Astrophotography Editor | Commercial – €230+VAT | Mac OS X, Windows, Linux

Pro

• It has all you need for astrophotography
• 45 days trial period
• A lot of tutorials and information available

Cons

• Expensive and without subscription plan
• Extremely steep learning curve
• Long and convoluted process
• Needs a powerful computer

When it comes to astrophotography, PixInsight is the software of reference against which all others are measured. It offers everything you may possibly need to produce pro graded images, and it is objectively the best software in the field.

But user experience can be frustrating, as the learning curve is very steep, the editing is long and convoluted, and your computer must be quite recent and powerful to make it run smoothly.

The €230 + VAT price tag is also quite steep: sure it is worth every penny, but this makes PI be even more the software of choice for professional and keen amateur astrophotographers.

A Comprehensive Demo About Image Stacking

In this video, I show you how easy it is to wet our feet with image stacking.

This is particularly true if you use Starry Landscape Stacker, Sequator, Deep Sky Stacker and Autostakkert!, as I showed in the video below.

Conclusion

Image stacking is one of the crucial steps in the astrophotography editing workflow.

You’ll need the appropriate stacker for each type of astrophotography: starry landscapes, star trails, or deep-sky and planetary images.

In this article, we have covered the most popular astrophotography stackers available on the market, both freeware and commercial.

And while Windows users have the more extensive choice, some notable stackers are available for Mac and even Linux users.

To stack, or not to stack? Most astrophotographers will agree it’s necessity with deep sky images, but is it really necessary for lunar imaging when the moon is so big and bright in the sky? There are a lot of single frame photos of the moon that show incredible detail, so is it really worthwhile going through the process of taking dozens, or even hundreds or thousands of images and then stacking them? Are the results really that visible? In this article, I we’ll go through the process of stacking a lunar image and see the results at each step along the way.

WHAT IS STACKING?

Stacking is a very familiar process to most astrophotographers. Unlike the days of film, there are no longer single 30+ minute exposures of celestial objects taken. These days, several shorter exposure are stacked together to create a final image.

Stacking – whether for deep sky or solar system – is the process of taking multiple images of the same object and digitally combining the images to increase the signal to noise ratio. With each additional stacked image, more signal is added to the final image while background noise is reduced. Those process of stacking deep sky and solar system images is completely different, but the end goal is the same – to bring out as much fine detail in an image while cancelling out digital noise.

This article will be focusing on lunar stacking. In this case, I won’t be covering the fine details of how to use each and every program used in the process, but will talk about the basic workflow that applies to any software you do this with.

THE PROCESS

These are the major steps involved in processing a solar system image. The mechanics of processing the moon, sun, or planets vary slightly in process and equipment, but they all contain these steps. There are different software programs that take care of each step, each requiring its own unique processes, but these are the main steps required.

Acquisition
Pre-processing
Stacking
Sharpening
Post-processing.

Acquisition

It all starts with taking your pictures. Solar system imaging is generally done with a dedicated webcam type camera attached to a telescope instead of a DSLR, and the camera shoots video instead of still frames. Since solar system objects are very bright compared to deep space objects, exposures of more than a few fractions of a second will blow them out completely. These webcams will typically shoot exposures of 30 to 100 frames per second, or 1/30th to 1/100th of a second. Generally, this is also the method used with a DSLR. The camera is set to capture high frame rate / low resolution video like 30-60 fps at 640 x 480 resolution. Planets are so small that they are still tiny in the field of view at that resolution. Planetary imaging is very difficult with a DSLR at prime focus and generally not recommended.

The moon, however, is a much bigger target. Using such a webcam results in very high magnification views of the moon. Craters will be seen in astounding detail, but if you wish to see the entire moon, a DSLR is the only way to go unless you want to take potentially dozens of videos, stack them into images and then create a full panorama of the moon.

For this lunar image, I used a Nikon D5100 attached to an Explore Scientific 80ED apochromatic telescope mounted on a Celestron Advanced VX mount. Tracking isn’t necessarily required to shoot the moon. You can also shoot the moon easily with a 300+mm lens on a stationary tripod. Since you won’t be tracking, you’ll have to manually readjust your framing from time to time to keep the moon in your field of view. You can also shoot the moon with a manually tracked telescope on any type of mount. Once again, you’ll need to readjust your framing every so often to keep the moon in frame.

For this project, I shot 470 images of the moon. My camera was set at ISO 100 with exposures of 1/160 of a second. I also shot 10 dark frames (images shot at the same setting but with lens cap on) to reduce noise. I could easily have also shot HD video of the moon at 30 fps with the same exposure settings and used the resulting video to process in the next step. Or for faster acquisition, I could have used my D750 at 60 fps. The end result would have been the same.

This is the RAW file as it came off the camera converted to JPG without any editing. The moon occupies a rather small space near the centre of the frame. It’s quite bright and very detailed. Many people would proudly share such an image online with little to no other post-processing and be quite happy with it. And rightfully so too. It’s a great image with sharp focus and good brightness. But with some processing work, we can do much better than this.

NOTE: If you’re using a DSLR, make sure to always shoot in RAW mode and never in JPG. And if you’re not dealing with video files, use TIFF as your intermediary format and only save out a JPG at the very end for your final image to share online. You want to maintain the highest possible quality through your workflow.

But zooming in on said image and examining it closer, fine detail shows that there is some visible pixellation and noise. Fine details such as craters are a bit blurry due to atmospheric distortion. And since the moon is so bright due to its advanced waxing gibbous stage, there’s very little contrast between light and dark areas.

Pre-Processing

The first step to preparing your images is to align your frames, crop them to size, and normalize the brightness. When shooting with a tracker or equatorial mount, alignment isn’t as critical. If your polar alignment and tracking are accurate, your target should be in the centre of the field of view throughout the entire series of images. However, if you were shooting full resolution stills instead of a video, you’ll see that the moon is but a small object in the centre of your image covering an area of anywhere from 800 x 800 to 1000 x 1000 pixels. Processing full 10+ MP still photos will take a LONG time, so this pre-processing step will save you a lot of time.

Not that even when shooting HD video at 1920 x 1080, you’ll still have a lot of black space on either side of your target. Pre-processing will remove this dead space making for much faster alignment and stacking.

For pre-processing, I use PIPP – Planetary Imaging PreProcessor. This free program is available for Windows, Linux and MacOS and I highly recommend it to anyone shooting and stacking images of solar system objects.

I loaded my images and my dark frames in their respective spots under the Source Files tab in PIPP. Since I put in a series of images, it automatically selected Join Mode since these are all pics of a single object. And I also selected the Solar/Lunar Full Disc under the Optimise Options For section. This is pretty self-explanatory.

From the Processing Options tab, I chose to stretch the histogram to 75% and set the black point to 0%. This reduced the overall image brightness a bit and ensured that all my different frames were at the exact same brightness and set my background to black. In this tab, I also chose to crop the image to 1200 x 1200. This left me the moon nicely framed with a bit of space around it.

From the Quality Options tab, I selected Enable Quality Estimation and Reorder Frames in Quality Order check boxes This will order the images from highest to lowest quality for later stacking.

From the Output Options tab, I chose the output format to be TIFF, which saves a series of TIFF files. AVI output is the default option and is perfect for lower resolution final images or 640 x 480 video, But I find larger video files sometimes don’t play nice with other stacking software, so I prefer saving images taken with my DSLR as TIFF. But either way should work.

Then finally, I ran the whole process. And this is the resulting image. This is just a single out of 470 frames that was exported from PIPP. The moon is nicely centred and the brightness neutralized. This will be the series of images that will imported in the next step for stacking.

Examining this zoomed-in section, you can see that the noise and pixellation that visible in the previous stage is gone. PIPP performed the dark frame subtraction from each individual image lowering noise levels significantly, It looks far smoother than the previous stage. Detail is still fuzzy and not very sharp, but the pixellation caused by the noise has been removed.

Stacking

Next comes the process of stacking the individual frames. There are several free programs for Windows, but I’m not personally aware of any available for Mac. There is a long, more painful way of doing this in Photoshop, but it’s very time-consuming and the steps are way beyond the scope of this article.

The 2 leading free programs used are Registax6 (RS6) and AutoStakkert!2 (AS2). RS6 is a favourite of many because it does both the stacking and sharpening stage. It’s basically an all-in-one tool for your solar system processeing, whereas AS2 only stacks. But more on sharpening later.

When stacking, the software will analyze each frame for quality. Since all my shots were of exceptional quality (all rated 98%+ in PiPP), I told AS2 to stack the top 90%, for a total of 414 frames.
This is the resulting image with everything stacked. Looking at the full image of the moon, you see it’s brighter than a single source frame. It’s completely smoothed out, is noise-free, and small details that were fuzzy and still pixellated in the last step are showing fine detail that wasn’t visible before.

At this stage, the fine detail still looks a little fuzzy, but you can see that there’s no noise, and fine detail that wasn’t visible in the original pre-processed image is now visible, albeit a little blurred. The image now needs to be sharpened to bring that fine detail into focus.

Sharpening

Sharpening is the act of deconvolution an image to deblur it. There are a couple of ways this can be done. This most common method is through wavelet sharpening using RS6. The other is using a deconvolution filter.

As I mentioned earlier, RS6 is the best free option out there for this process, which makes it a good all-in-one package. You can go right into sharpening after stacking. Or alternately, you can import an image file that was stacked in another program for wavelet sharpening. I won’t go into details on the mechanics of using RS6. There are lots of videos on YouTube that can explain how it works far better than I can. But this will be the method that most people will use.

For deconvolution, there are no free options that I’m aware of. I use Astra Image. which costs $29.95 US. And there are some paid Photoshop plugins that will do this as well. I can’t recommend any of them, as I haven’t used them personally.

For this image, I opened my stacked image in Astra Image and ran the Deconvolution for Sharpening filter, From this, I chose the Lucy-Richardson Deconvolution and adjusted it accordingly, And this was the result. On this large scale, you can see fine details in the surface that weren’t visible at any of the previous stages. Large structures like craters, peaks and valleys are clearly visible. There’s far more visible relief on the surface detail than you could see before.

The same area zoomed in shows incredibly fine detail. Small rilles and craters are clearly visible. crater Clavius and its smaller craters pop out distinctly. The ridge on the edge of Tycho is clear and sharp. The image is clear, crisp and noise-free. At this point, all that’s left is final cosmetic touch-ups in Photoshop.

Post-processing

This is where the final touch-ups are made in terms of colour, brightnesses and balance. This last step is where some artistic licence comes in. This can be done in Photoshop, Lightroom, or whatever other software you normally use.

For this, I opened the my file in Photoshop CC and opened up Camera Raw. I made the appropriate adjustments to exposure, contrast, highlights and shadows, to my personal taste just as I would do in Lightroom and applied my DAA watermark. And the final image is now complete.

And as you can see in this same section zoomed in on the final image, the details just jump out. The contrast between light and dark areas is much more distinct. Small craters everywhere stand out. Ejecta lines that were washed out in the source images show up in clear detail.

THE RESULTS

So I think the original question has been answered. Stacking is definitely worth it on lunar images shot with a DSLR. Regardless how good your camera, equipment or technique is, you can’t match the results of a stacked image in a single frame. Sure, you can get some great single images of the moon, but you just can’t compete with a well processed, stacked image in terms of fine detail.

Hopefully this will be of help to aspiring astrophotographers who want to take great shots of the moon.

And as always, clear skies, and keep those eyes and lenses pointed up!