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.

Sneaky Night (and Daylight) Photo Processing Tips

 

Did you attend the Sneaky Night (and Daylight) Photography Processing Tips event held at Adobe in San Jose, California on July 23, 2018? Welcome!

The topics covered include these:

Let’s Start With a Pop Quiz

The Equation…

Or asked another way. Do these look like they might be the makings of an interesting shot?

Three Nuns Thumbnails

The Answer To the Pop Quiz

Combining the images shown in the thumbnails, nets this Interesting star trail.

N-604259-361lstr

“Long Streaks” Star Trail from 112 separate photos

Creating the Star Trail component above is discussed in detail in our NP105: Creating Star Trails & Timestacks Webinar – it’s an interactive 2 hour course with notes, a recording, and practice files. We run that webinar approximately quarterly next event is July 25th. Details  covered include how to set up the shots, configure the camera settings, and combine the images using various tools.

Adding that bright frame with a bit of selection and masking to the star trail image nets this:Reaching for the Sky

And that MUST be interesting because it garnered 80,000 views in just a few days. How do you do this bit of Photoshop Magic? Over the years, we’ve shown quite a few methods for accomplishing this. For example in Foreground – o – Matic we illustrated how to use the quick selection tool. That may work well here because the rock has a nice crisp boundary. Other methods that may work include “thresholding” and Color Range selection.

Thresholding to create a mask:  We’ve described this before. Briefly this is how it works. Select one of the images – one with contrast between the sky and foreground.  Duplicate that image (Ctl/Cmd -> J). Then use Image -> Adjustments -> Thresholds and slide the carat left or right until it has selected what you want (mostly black or white). Paint out the stray areas with either a 100% black or white brush as appropriate.  When done, you have an image you can use as a layer mask. The trick to doing this is to select the black and white image, EDIT an existing layer mask, and paste the black and white image as the layer mask.

 

Photoshop Processing Tips

  • Do work on a calibrated free-standing display in a dim, consistently lit room.
  • Do NOT attempt to process important images on a laptop monitor. You will frustrate the dickens out of yourself trying to get consistent color, brightness, and so forth on a laptop monitor or in an uncontrolled lighting environment. The monitor display angle can cause subtle to dramatic differences in color, saturation, brightness.
  • Do make an action and assign it to a hot-key if you find yourself repeating that operation frequently… E.g. I have an F9 key to apply a contrast enhancement adjustment curve
  • Do name your layers sensibly. You may save yourself a world of hurt.
  • Do NOT crop too early – save this step for last.
  • When combining dark and light subjects (e.g. daylight-like and night) it’s usually best to have very crisp selections – not feathered selections.

Gallery of Photoshop Hot Keys

These hot-keys are described for Windows users. I use these ALL the time. Some have no menu equivalent. You can translate from Windows to Mac as follows:

Ctl -> Command
Alt -> Option
Shift -> Shift

Layer / Layer Mask shortcuts:

  • Duplicate layer dialog allows you to duplicate into another/new document!
  • Ctl-J: Duplicate the current layer
  • CtlAltShift-E   Merge visible layers to a new layer as a COPY.
  • Shiftclick on layer mask to turn it off or on.
  • Ctldrag layer mask to move it to another layer.
  • Shiftdrag a layer mask to Invert it and move it to another layer
  • Altclick a layer mask to EDIT it.
  • Altdrag a layer mask to copy it. Toss in Shift to invert the mask.
  • Shiftclick a layer mask to turn it on/off
  • Altclick quick mask icon to create an inverse layer mask from a selection
  • Do not be afraid to duplicate and adjust a layer for the sole purpose of creating a mask!

Selection shortcuts:

  • Ctlclick on layer mask to create a selection from that layer mask.
  • Ctlclick on a channel e.g. RGB, R, G, or B to make a selection based on brightness.
  • Sometimes Select -> Modify -> Expand or Contract (by 1 pixel) helps to fine-tune a selection. Feathering seldom works well for compositing light and dark images.


Sneaky Tips
Sneaky Tips
Notes from "Sneaky Tips for Processing Day and Night Photography"

Landscape Astrophotography

Thanks for attending my Landscape Astrophotography discourse with the San Jose Astronomical Association on Tuesday, June 19, 2018. 7:30 PM to 10:00 PM. Most of the audience are Astrophotographers.

Below is a form you can fill out and we will email you a PDF of the notes from this lecture.  Following are some brief excerpts from the talk.

The Meeting of Earth and Sky

Big Sur, California, has earned a reputation for being The Greatest Meeting of Land & Sea, a phrase attributed to Robinson Jeffers, the “Walt Whitman” of the West Coast. Indeed living here is inspiring. The towering cliffs and mountains, lush forests, crashing, craggy Pacific surf all work together to evoke a sense of beauty and wonder that is astonishingly intimate.  There are certainly other beautiful places in the world – even nearby. But I believe that there is awesome, virtually undiscovered beauty that touches nearly everywhere in the world: the night sky.

Night Sky photography has grown by leaps and bounds in the last decades. Prior to the age of digital photography, there were relatively few painters of the night sky. Not surprisingly, none of those painters painted just stars. All featured stars with landscapes. Perhaps the most well-known painter of the night is Vincent Van Gogh. In Van Gogh’s day, light pollution was far, far less noxious than it is now. Indeed our super abundance of artificial light has rendered our night sky almost unobservable. But the night sky has such depth and mystery that everyone should find a dark sky to sit under for a time. Part of the allure of the night sky is its expansiveness… its immense scale.

Because the scale of the night sky is difficult to grasp I believe it is important to link human-scale to the starry night. Deep-sky photography of nebula and galaxies reveals things completely unseen or unseeable by the naked eye – and the revelation of those objects is  compelling and engaging. But even more compelling are photographs that tie humanly identifiable scale to the mysterious night.

In addition to scale, compelling photographs reveal the unexpected. Photographs can show time, location, relationships, colors, and details that are unobservable by looking. To draw lay people, however, I believe there must be a strong link between what is observable with what is not: a Marriage of Earth and Sky. And for that reason, I’m urging Astrophotographers and astronomers to try Landscape Astrophotography.

As Numerous as the Grains of Sand

This is truly a meeting of Land, Sea and Sky

For more details, please see the accompanying notes.



Landscape Astrophotography Notes
Landscape Astrophotography Notes
71+ Pages of notes covering the following topics:
  1. How to Make Images Memorable
    • Scale / Grandeur
    • Connectedness
    • Interest
    • Revelation
  2. Impact of Photos
  3. How to Create Scale / Grandeur
  4. How to Connect - Interest and Familiarity
  5. Revelatory Photographs
    • Time | Location | Relationships | Familiarity | Seeing Differently | Surprising Colors | Intricate Detail
  6. Inspiration from Painting
  7. A sense of place
  8. An Astrophotography Idea
  9. Conclusion
  10. Resources and References

 

Other articles on this site that you may find relevant include:

Basics: Setting Up Your Tripod

Hello folks. I’m not going to get all parochial on you here, but in teaching workshops and rubbing shoulders with other photographers I see lots of people struggling with setting up their tripods – some of them don’t even know that they are struggling. If it makes you feel any better, I once set up my tripod in such a way that it flopped over and snapped a $1400 lens in half. I’ve also witnessed a fellow photographer’s rig topple over, fall on to rocks below and in the process smash his lens to smithereens and create a hole in his camera body. Need more motivation?  Six students had their tripods topple over when shooting at an event where there was gusty wind. None of them had done what we recommend below.

If you’re sure you know how to solidly set up your tripod and how to prevent an expensive catastrophe, well, you probably stopped reading when you saw the title of the article.

Rock Garden - Wide Range

Using a tripod correctly in terrain like this is a valuable (sanity preserving) skill

Still here? There is no substitute for using a sturdy tripod as we described earlier. However an improperly set-up tripod will give you a false sense of security.

Lets be sure we have terminology straight:

Feet: The part of the tripod that touches the ground – the bottom of the legs.
Legs: The (often telescoping) section of the tripod. Legs are made secure using
Leg Locks: which are of two general types: flip locks and screw locks (shown). We prefer the latter.
Leg Pivots: The upper side of the legs attach to the BASE where the legs can be made to pivot inward or outward. Usually there are options for specific pivot angles.
Tripod Base: The leg pivots are on the underside of the base.
Center Column & Center Column lock: If the tripod has an extensible section separate from the legs, it usually fits through the base and has a lock to secure the center column height. Some center columns also have a hook at the bottom (as shown).
Base Plate: The top surface of a center column (or the top surface of a base) to which the head is attached.
Head: The purpose of the head is to allow the camera to rotate and tilt. There are two principle types of heads: ball heads (shown) and pan/tilt heads.
Quick Release Clamp: the upper surface of the head usually has a clamp/plate system to make it easy to mount and unmount a camera. Arca-Swiss is the most popular clamp/plate system.
Quick Release Plate: attach securely to the camera and is held by the QR clamp.
Camera: the reason you have all the preceding stuff.


The Basics

Vertical: Your tripod should be vertical, specifically the center column (if you have one) should point straight up and down. The more vertical, the more stable the tripod is. By vertical, we don’t mean perpendicular to the ground – the ground may be sloping or irregular. The most common mistake people make is to set their tripods up so that it leans toward them.  Before you put your camera on your tripod, walk around the whole thing (safely) to judge the verticality.  You can even use a level (e.g. a smart phone app) against the center column to be sure it is vertical. Some tripods have a bubble level on the base – and some heads have a level on their base – that you can use to be sure your tripod base is level.

Notice tripod in the distance is leaning to the right (click for a bigger view)? That’s wrong!

Level: For many reasons, you want the base to be level (perpendicular to vertical). If your tripod is vertical, the base will be level. A level base makes panning (and thus panoramas) more accurate. If the base isn’t level rotating the camera may change the center of gravity causing wobble – or worse.

Legs: There are two adjustments here: the leg length and the leg spreadDO NOT fully extend the leg lengths – unless you are on flat, level ground. Adjust the legs so the base is level.

  • When on a slope, put two legs on the downhill side of the slope and one leg on the uphill side.
  • Place two legs at the front (that is where the camera is pointing) and one leg toward the rear.

If these two goals conflict, prefer two-legs downhill. A single leg at the front may intrude into a wide-angle shot. Most tripods have adjustable leg spreads. Each leg can form a medium, moderate or severe angle to the base. On irregular terrain, you may find that stability requires setting one or more legs at a different spread and different lengths. E.g. one leg is kept short at 90 degrees to allow that leg to rest on a boulder while the other two are more vertical. In a multi-segment tripod leg, the wider leg segments are more stable than the narrower ones, therefore:

  • Extend the wider leg segments fully before extending the narrower leg segments.

TIP 1: We find the screw-type leg locks to be the most secure and easiest to adjust. What we do is to grasp and loosen all the leg locks at once by a quarter turn. Fully extend all sections. Tighten the top locks fully (and middle locks – if you have 4 segment legs), then loosely tighten the smallest leg locks. When setting the tripod down you can gently push down each of the legs until it is vertical and level, then fully tighten the lower leg locks. Minor fine tuning can be achieved by loosening the upper leg locks.

  • If in windy conditions, set the tripod lower than normal and spread the legs wider. Also weight the system more heavily (see Weight, below).

Center Column (and tripod height): DO NOT extend the tripod fully just because you can. Extend the column as little as needed. The center column is useful for fine-tuning the height of the camera, but it raises the center of gravity and makes your tripod less stable. Likewise making your tripod as tall as possible makes it easier for gusty wind or and inadvertent bump to topple everything.

Tie-Stake Useful in some terrains

Weight: We HIGHLY recommend adding weight to your tripod. Many tripods have hooks on the underside of the base or on the bottom of the center column. We regularly hang our camera bag from that hook. But beware: if your camera bag is too light or bulky, you may end up adding a sail that catches the wind and creates instability. Some people bring weights, or bags they can fill on site with rocks or sand. But there are yet two more tricks you can employ:

  • Hang your camera bag so that it nearly touches the ground (by using a lower tripod position, or a strap between the bag and the tripod). Then place rocks or logs around the bag to keep the bag from swaying. Add heavy things in to the bag if you need more weight.
  • Bring a tie-down stake and a bungee cord. Screw the stake into the ground below your camera and snug the tripod hook to the stake with a bungee cord.

 

Straps: If you have shoulder or wrist straps on your camera we recommend using removable ones OR use twist ties or velcro wraps to secure the straps to your tripod so the straps do NOT catch the wind (or nearby objects). Shoulder straps can become like sails and even if they don’t catch enough wind to topple your tripod, they can induce vibration. We really like OP/Tech products, by the way. They are well designed and have never failed us.

Tip 2: One way to practice setting up a tripod is to do it indoors. Create un-even scenarios by resting one (or more) of the legs on a chair, wastebasket, etc. Practice getting the legs adjusted in a way that keeps the center column vertical and the base level.

Sailors

Sailors: Timestack of 114 images during sunset/blue hour in Alabama Hills, California

Safety Checks

After setting up your tripod as described above, you can and should test the stability of your tripod/camera. WHILE HOLDING ON TO THE CAMERA STRAP(s) do each of these checks:

  1. Pull down on each of the legs gently. Make sure they don’t collapse/fold.
  2. After clamping the camera to the head and tensioning the head. Hold the camera snugly and try wriggling the camera out of the clamp. Watch carefully for wobble and hold on securely in case the camera does come out of the clamp.
  3. Hold the camera, release tension on the head and let the camera gently flop. Make sure that when the camera flops the system doesn’t topple.
  4. Leave the camera in its flopped state and rotate 360 degrees checking for wobble.
  5. Repoint the camera, tighten the tension and gently bump the camera. Make sure there is no wobble.
  6. Bump each of the legs. Make sure the legs don’t become dislodged and the spread doesn’t change.
  7. Take one more lap around your camera checking for verticality and possible instability – e.g. a log, tree branch, stick or rock that could bump your tripod.

Is all of the above really necessary? Well, no. You don’t have to do any of that… unless you want to protect your equipment and take nice stable photos.

Here is my son with the tripod legs set wide, and the center column inverted to get the camera low to the ground.Photographer at Work [5_005398]

Want tips on other gear to carry… see this article. Would you like to see all of our best tips in one place? Try this article. Have a great tip on tripods we should know? Please share it in a comment!