Tag Archives: stacking

Stacking: the Overloaded Word That Needs Explanation

The current rage of “stacked Milky Way” (or night sky) captures is quite different from the star trail or timestacks style of captures. Huh? The words stack and stacking are overloaded with many different meanings. Let’s see if we can add some precision and clarification.

Here are some of the variations possible:

  • Auto Blend Layers with Stacking: Used for macro/focus stacking, HDR, and generic image blending – NOT for astro images!
  • Lighten Mode Stacking: Creating Star Trails!
  • Statistics Mode Blending (Stacking): Can perform the same operation as Lighten Mode Stacking when the option “Maximum” is used, however Statistics are heavy weight and more complicated to do in our opinion.
  • Align and Stack: Deep sky astrophotography using several images taken one after another as quickly as possible. Photoshop doesn’t do this well, but we describe how in the next section. Align is the distinguishing word here.
  • Tracked Stacked Images: For still astrophotography images with less noise and greater detail. A device is required that tracks the sky rotation – the word tracked is the key here.

    Adobe Lightroom and Adobe Bridge “Stacking”

  • Group into Stack:  Not stacking at all! It really just means “create a group”.

The above is NOT an exhaustive list of the kinds of stacking you may hear about!

Stacking Types Explained

Group into Stack

Let’s start with the easy one: Stacking may mean add to group. In Lightroom and Adobe Bridge you can pick several photos and the options  Stacking -> Group into Stack. Or pick several photos and either Photo Merge to HDR or Panorama with the “Create Stack” option checked. In this context, Stacking and Stack just means group.  Unfortunately a photo can only appear in one stack, and you cannot stack photos from different folders together.

Why would you want a photo to appear in two (or more) stacks groups? Here is an example where I used a single top shot and created two different panoramas.

Panoramas 1 and 2 were both created using image 3 (608095.NEF) but when panorama 2 was created, image 3 was removed from the stack (group) for 1 and added to the stack (group) with 2. Furthermore, you can see that the panorama and the two photos used to create it were all added into the group (notice the last image says 3 of 3).

Blend Layers using Lighten Mode

Stacking may mean blend photos in lighten or darken blend mode – examples are star trails and timestacks. In this usage, the lightest (or darkest) of all the pixels in each image is selected. This is the kind of stacking that AdvancedStacker Plus does. Below is an example of taking several images that we collected over time with long delays between each exposure causing the “dotted” appearance of the star trail.

Several layers of images taken at intervals all set to blend mode “Lighten”

Align and Blend Stacking

Stacking can ALSO mean ALIGN and blend images with median, mean (aka average) or more sophisticated algorithms. Indeed astroimagers have been doing this style of blending for years using techniques that involve “star registration” (aligning stars with stars) and some pretty fancy stacking algorithms like Alpha-Kappa Median Clipping and Entropy Weighted Average. The key point here is the alignment. Indeed, here at StarCircleAcademy, we’ve explained how you can brighten and reduce noise in your foreground using simple astrophotography processing techniques.  See below for how to accomplish Align and Blend Stacking in Photoshop, and plenty of warnings about why this method is very likely to FAIL using Photoshop as the tool.

You may also see references to tracked, stacked images. These are the same as “align and blend” just described, except that to capture the image, the camera is guided by an external device (or by some fancy internal hardware), to allow longer exposures of the stars without getting unintentional trailing (smears) of stars.

The takeaway is that not all stacking is created equal. You need to know the context to understand what is meant by the word: stacking.

Focus Stacking / Auto Blend Layers

In Photoshop there is Edit -> Auto-Blend Layers -> Stack Images this is yet another kind of stacking (focus stacking) and despite the wording is NOT the kind of operation needed to ALIGN and Blend astro images. If you don’t believe us, give it a try and you’ll see it will do very weird things with your layers. Below are the same images as earlier. Note the bizarre masks it created to do the blending.

Edit -> Auto-Blend Layers -> Stack Images makes a mess. We told you so! Click to see a bigger image.


Aligned, Stacked Starry Landscape Images

While it would probably be better to make this a separate article in itself, we found it painful enough that we don’t recommend bothering – and yet we proceed to explain HOW to do it anyway!

If you want the cleanest possible images, you’ll – of course – want to reduce the overall noise  and bring out details by using many images instead of one. This approach is not all puppies and kittens. Here are some of the pitfalls:

  1. The direction of sky movement relative to the ground has a significant influence on the quality of the result (as well as the order chosen for alignment). In general, setting constellations are better than rising ones.
  2. Most of the existing tutorials will assume that you have a recent (CC) version of Photoshop with statistics and an an “Auto Align” that properly manages masked regions.
  3. Some of the tutorials we’ve observed are more cumbersome than they need be. There are plenty of hotkeys and mouse shortcuts to make the process go pretty quickly.
  4. More than 10 or so images can become quite demanding on machine resources.
  5. The complexity of your foreground will also affect the outcome. A clean, crisp separation between sky and land is preferable. Trees, poles, wires, and other things that extend through the sky are problematic.
  6. Lens distortion can also adversely affect the outcome.

Aligned Stacking Procedure

  1. Load all the photos as layers in Photoshop.
  2. Heal out airplane and satellite trails from each layer.
  3. Select all the layers and add to a group named “Sky
  4. Right click the Sky Group and duplicate the whole group as “Foreground”
  5. Select all the layers in Foreground.  Use Layer -> Smart Object -> Convert to Smart Object.
  6. Select Layer -> Smart Object -> Stack Mode -> Mean
  7. Duplicate Mean using Ctl-Alt-Shift-E (Command-Option-Shift-E on MAC). Label the newly created layer “Mean” and turn it off.
  8. Select all layers in Sky. Set blend mode to “Lighten” and observe the direction of star movement against the ground.
  9. Be sure the image with stars nearest the ground is at the BOTTOM of the stack. The bottom layer will be your base for alignment. You can drag layers around, or Layer -> Arrange -> Reverse may do the trick.
  10. Create a mask keeping as much of the sky as is easy to do but that DOESN’T include any ground  or fixed location objects. IMPORTANT: Be sure the mask doesn’t have holes in it, including at the bottom corners. Click the layer mask, hold down the Alt (Option) key and drag the mask to the next sky layer. Repeat until all sky images are masked with the same mask.
  11. Select the bottom layer and lock it  (Layers -> Lock Layers -> check Position -> Ok)
  12. Select all the sky layers.
  13. Chose Edit -> Auto Align Layers -> Auto
  14. When alignment is done, set blend mode for all sky layers to Darken. If stars are disappearing in the result image, that’s bad.
    1. If alignment is great everywhere, that is you have plenty of stars, you’re done. But it probably won’t be. So…
    2. Duplicate the current layers to a NEW document – call it whatever you want, but perhaps “Left looks good” makes sense.
    3. Open the history palette and click just above the “Align Layers” item (to restore to before the alignment was done). Lock the TOP layer (see item 11) and repeat steps 12-14.
    4. If a large portion of the image still has streaks in some quadrant, try undoing align, undoing the lock and re-aligning.
    5. If you’re still getting a significant amount of streaking you can also try Auto Align -> Reposition rather than auto.

      Q: Why do I have disappearing stars?
      A: The reason they are disappearing is because they are not aligned. In Darken mode, the darker sky “wins” out over the several stars. This COULD be a good thing in other situations, but not here!

      Q: If I went through the trouble of doing all this alignment, why is it still “off”?
      A: Photoshop isn’t optimized to align stars. Secondly, lens distortion makes a star move non-uniformly across the sensor. And third: stars at different declinations (celestial latitudes) travel at different speeds across the field. To eliminate streaks, the best solution is to track the sky.


  15. Take the aligned sky, delete all the layer masks. With all the aligned sky layers selected, create a smart Object.
  16. Do the same Stack Mode “Mean” trick for the sky smart object that you previously did for the foreground.
  17. The rest is pretty straight forward. Turn the foreground (mean) back on. Use a selection to reveal only the foreground and apply that to the Foreground Group.
  18. Adjust contrast, color balance, vibrance, etc. to your satisfaction.
  19. Save the kit and caboodle.

Does all this seem too complicated? Well, then perhaps you might consider using these tools instead. They do most of the hard work for you and they KNOW the difference between stars and foreground (usually because you help them know).

  • On a Mac: Starry Landscape Stacker – from the Mac App Store
  • On a PC: Sequator – do a Google Search to download it.

By the way there are many astro processing tools, like Deep Sky Stacker – but most/all of them expect that your images will have NO foreground or non-moving objects like wires in them.

Darken Mode Stack Tip Using AdvancedStacker PLUS 18

Published: March 15, 2018

The new Advanced Stacker PLUS 18 is our attempt to make processing simpler. One of the things we find we often do is run multiple stacks (Lighten, Darken, Streaks, etc) to determine which effect(s) work the best. Well, we did something for the first time that worked REALLY well, so we will start by sharing that, even though Advanced Stacker PLUS 18 is not yet ready for publication.

In a nutshell, we created this:

Orion, Falling

From this:

Long Streaks Stack Result – no modifications  f/4, ISO 1600, 15 Seconds. Nikon D600, 24mm x 250

There are several obvious differences between these images.

  1. Because there was strong moonlight (and other light), the sky is over-bright and lacks contrast.
  2. The wind together with surrounding lighting (including flashing red lights from a passing fire truck) caused strange artifacts in the palm trees.
  3. Different colored light sources lit the palm trees differently (notice the really cyan colored palm fronds in the second tree from the left).
  4. There was utility wiring intruding into the image.

The Processing

Stacker 18 allows you to simultaneously stack in multiple modes. For example, to create this effort I used Lighten, Long Streaks, Darkest, and Average modes. I ended up NOT using Lighten or Average modes in this case. Is there extra overhead keeping more stacks? Yes, there is. However we’ve paired down the stacks to as few frames as possible to keep the overall footprint low.

Once the stacking had finished, the result of the Long Streaks was a bit unappetizing due to the red and other artifacts in the trees (see second image). However the Darkest mode stack effectively removes all of the stars – and as it happens, all of the strange highlights in the trees.  First we applied a Curves adjustment layer to the Long Streaks and darkened it.

Blending a Clean Foreground with the Star Trails

Darkest Stack results

The next operation was to find a way to blend the darkest mode stack (right) with the Long Streaks stack while preserving the star trails  and getting the cleaner looking foreground.

 

Duplicate the Darkest mode result (it’s a single layer) on to the Long Streaks stack. Then drag the darkest mode stack to the top layer. Set the new layer blend mode to normal, 100%.

Next we need to mask out the sky of the Darkest stack so that the long streaks will show through. The tool for that is to use Select -> Color Range. Holding down the shift key allows you to click multiple areas of the sky to add to the selection. You can vary the fuzziness of the selection to determine how closely the color has to match the sample. The mask will probably need some manual cleanup afterward, but as you can tell from the selection in the image below, just clicking different areas in the sky produced almost exactly what is desired.

Photoshop Color Range Selection

After pressing OK you get a selection. The next step is Layer -> Create Layer Mask from Selection -> Hide Selection Once you have a mask, you can paint on it to clean up any artifacts. Adjust the opacity of the darkest layer to make it “look right”. In this example, the combined image looked best at about 93% opacity.

Correcting “Off” Colors Due to Light Source Issues

The penultimate step was to create a Hue and Saturation adjustment layer. Lock the adjustment to the Darkest layer (hold the Alt/Option key and click on the boundary between the adjustment and the darkest layer). Then click the “Finger selection”  (just below the word Presets). Now there is an eye-dropper which you use to select the color that needs correction. In this case, clicking the dropper on the cyan colored palm frond is the right move. Adjust the saturation slider way down, lightness down, and fiddle with the hue to make the bizarre color more natural.

Aggressively toning down the cyan colored palm fronds

Removing Wires (and other distractions)

Finally we also used the Spot Healing Brush tool to “heal out” the utility wires. Here is a short-cut for healing out a straight line. Click the beginning of the area with the spot healing brush, then hold shift and click the end of the line. Shift causes the brush to be applied in a straight line between the first and second clicked points. The shift-trick works with almost all brushes. Two other tricks with the spot healing brush tool are to:

  • Start where the surrounding area has a predictable substitution (not a busy area) and work outward from there
  • Use as small a brush as you reasonably can

For example you can adjust the spot healing tool brush size to about double the width of the utility line, then click the healing brush tool where the arrows point below. Next work your way outward toward the tree on one side, then the other.

Summary

Here is a summary of the steps taken – not including the palm frond “naturalization” or spot healing described above.One more trick worth noting… the histogram shown on the Curves adjustment will give you a clue what may need adjustment.

Want to know what we consider the top 5 most used photo editing skills? Read here (and part 2 and part 3).

Time Stacks

Published: March 6, 2018

One of the great things about developing a repertoire of tools  and tricks for processing photos is applying those tools in creative ways. While we were furiously working on Advanced Stacker PLUS for creating star trails and processing night sky images, one clever fellow: Matt Molloy gained great acclaim by stacking sunset and sunrise shots of clouds skittering across the sky. Matt Molloy coined the phrase Time Stacks for that type of image.

Phoenix Leaping

Phoenix Leaping – 20 separate frames combined in Lighten Mode plus an extra foreground frame.

Where Steven lives in the Silicon Valley, it is difficult to get good conditions for clouds. Indeed, the San Francisco Bay Area has so many blue sky days that having clouds is a stretch – in the Bay Area the options are either low thick clouds (fog), or zero clouds. However occasionally conditions are right – or Steven travels where conditions are right – for creating these shots. Of note are dry climates with mountains and high winds during seasons with moderate moisture in the air. In March in Palm Springs, California, for example Steven watched as clouds formed due to the uplift of the Mt. San Jacinto mountain range and dissipated quickly as the young cloud wandered eastward away from the peak. Literally you could watch clouds form and dissolve in a matter of minutes. In the image above, you’ll notice that some low clouds moved slowly and didn’t dissipate. Because the denser low clouds were in the shadow of the mountain they grew dark and ominous.  You can see more variations on the same theme by checking out this set of images.

Exit Criteria

Exit Criteria – Alviso, California on one of the few days when clouds were present

What Conditions and Equipment Do I Need?

  1. You need partially cloudy skies and the clouds can not be slow creepers. The clouds should be vigorous sailors. How fast? Fast enough to cross a significant field of view in about 20 to 30 minutes. They need to move into an open area of the sky – clouds moving over other clouds won’t be as interesting.
  2. Like any compelling shot, the frame should include a worthwhile foreground.
  3. And finally, it helps if these conditions all occur near sunset or sunrise so you can get extra color in the shot.

Equipment

  • You will definitely want to use an Intervalometer (or an on-board Intervalometer if your camera has one). Shooting at regular intervals results in a more pleasing outcome.
  • A sturdy tripod is also a must.

What Settings Should I Use?

  1. Select a moderate aperture (f/8, for example), and a low ISO (200). The goal is to get a shot that is relatively long to get a little cloud blur from the cloud motion.
  2. Since most interesting results occur right at or after sunset, start the exposures at 1 to 2 stops over exposed. Subsequent shots will get darker and finally dark to a point where the images will be too dark  to use (e.g. 2 stops under exposed).
  3. While it may be tempting to adjust the exposure during shooting, we have found that strategy does not work well.  You never really know which shots you will want to combine. Therefore it is best to do large sets (40-50 exposures) all using the same settings.
  4. Change settings (and optionally re-orient your camera), then get another substantial sequence.
  5. Be sure to include an exposure optimized for the foreground in the beginning and/or at the end of each sequence.

The trickiest part is selecting the interval between shots. The speed of the clouds across the frame is the key here – and that can vary dramatically depending on your conditions. One possible method is to shoot once every other second, then cull out the interval that works best (which could be 10 or 20 second intervals), but a less memory and processing intensive approach may be to use 5 or 10 second intervals between shots (or longer if your clouds are sluggish).

Also keep in mind that not all clouds will move at the same speed (or in the same direction!), nor will they be illuminated alike.

How Do I Process the Shots?

This is actually the easy part: use the same tools you would use to create star trails. That is, stack the images in Lighten mode. Understand that if clouds move over clouds the net result is sometimes quite unexpected – the brighter clouds (regardless of color) win.

How Processing Was Completed (Click for larger image)

Above is a snapshot illustrating how this shot (62 frames in the life of clouds) was finished in Photoshop. Two image contrast enhancements were added. The bottom layer is the stacked (lighten mode) image, the next image up is the intentionally over-exposed foreground. Notice that the “Darken bright foreground” is linked to effect ONLY the foreground image. Also note that darkening, and in many cases increasing contrast has the affect of increasing color saturation. No saturation or vibrance enhancements were done here. As with Star Trails, we also recommend that you do not alter any of your shots before you stack them – stack them in their raw form with NO adjustments. The result will look flat until you apply manual corrections and curves, but by not altering your shots before hand, the stack will work better and you are far less likely to introduce strange artifacts.

Variations on Time Stacks

Of course your Time Stacks do not have to be daylight subjects like this solar eclipse which was shot with a solar filter for all the shots except the last which was taken at sunset.

Annular Eclipse Sequence [C_040079+5s]

Time stacks can also include night events like a lunar eclipse

Plan C: San Jose City Hall Eclipse Sequence

Get creative and try other Time Stacks and share with us what you get as a result via comments!

Want to see the technique preferred by Matt Molloy, master time stacker? See his tutorial here.

Look What You Did!

First we really appreciate the mastery of Matt Molloy who has been using the Advanced Stacker PLUS to reach creative new heights in “TimeStacks”.  This is one of his images below in which he stacks part of the image with Comet mode, and the rest with lighten mode. Click the image to read more.

Reach for the Clouds by Matt Molloy

Reach for the Clouds by Matt Molloy

We invited users of the Advanced Stacker PLUS to give us feedback on their experiences with our Photoshop Add-in. We asked folks is if they had an image that they made with the software that they’d like us to see. Wow. We are impressed! Take a look for yourself. We used the links provided so none of the images shown are on our server. In other words, if an image does not load properly, there is nothing we at StarCircleAcademy can do to fix the issue.  Where possible, clicking the image will take you to the photographer’s site.

Version 14E is available now, by the way.

If your image appears here and you’d rather it did not, let us know and we’ll remove it.

Exit Criteria

Exit Criteria by Steven Christenson (channeling Matt Molloy)

Rocky Mtns

Rocky Mountains by Bob Gibbon

The Chalice by John Mu

The Chalice by John Mumaw

Church by Bob Edwards

Church by Bob Edwards

Lassen Campfire Pano 1

Lassen Campfire Pano 1

Red River Camping Spot Star Trails by Jeff Stephens

Red River Camping Spot Star Trails by Jeff Stephens


Starflight over Pointy Land

Starflight over Pointy Land by Steven Christenson

Chapel in Starlight by Keith Doucet

Chapel in Starlight by Keith Doucet