Category 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.

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"

Why Aim North?

Reaching for the Sky

Reaching for the Sky: 112 images, each f/4, ISO 800 for 60 seconds including a shot from twilight hour for the foreground Alabama Hills, Lone Pine, California

Want to capture Perseid meteors, the Milky Way, and star trails in an awesome location?

Join us for our>>> Field Event: Meteors, Milk Way in Alabama Hills <<<Sunday, August 12, 2018 (with an optional second night).  SORRY EVENT IS FULL

I live and travel in the Northern Hemisphere. In fact I have yet to travel south of the equator, so my apologies to those of you from the southern half of the planet for my obvious northern bias.  I believe those of you in the bottom half of the planet can just substitute the word South for North everywhere and everything should be correct.  I have added [parenthetical content for those who are in the southern hemisphere where that north/south swap doesn’t work]

The results obtained by shooting a long exposure at night depend quite a lot on which direction the camera is pointed. I favor long star exposures with a northern view for many reasons.

The Advantages of Shooting To the North

  1. Curvature of the star trails is strongest around the north star. Exposures of about 6 hours will appear to be full circles (24 hours of exposures are actually needed to make complete circles and that is not possible in one night except near the North Pole!).
  2. The moon will never intervene into the shot because the moon never passes through the northern sky.  [NOTE: those in the southern hemisphere still have to worry about a moon in their Southern shots]
  3. Cassiopeia and Ursa Major (the Big Dipper) are bright constellations that can always be found in the Northern Sky – so there is always some interesting sweep of stars possible. The region immediately around the North Star, however has dimmer stars which may only be captured through long exposures. [The southern hemisphere suffers for lack of many bright constellations near the southern celestial equator]
  4. With just a smidgen of star hopping skill it is easy to find the north star which, weather permitting, is always visible in the night sky.
  5. The moon sweeps east to west giving long shadows from the right or left of the subject. And when the moon is highest in the sky it can cast strong face light.
  6. The sun also never appears in the northern sky so it is safe to leave a camera running from before sundown to after sun up. Camera damage can result from a long exposure pointed at the sun.  [NOTE: those in the southern hemisphere still have to worry about a sun in their Southern shots]
  7. Since the moon cannot enter into a northern shot a photo can be made regardless of the moon’s phase and for as long as I choose. For shots toward the East, South or West it is important to know the moon phase and location during the hours of shooting to prevent problems from flare or washout. [NOTE: those in the southern hemisphere still have to worry about a moon in their Southern shots].
  8. The stars in the north move the slowest through the field of view which allows them to be brighter and reduces inter-exposure gaps in the trails.
  9. If I know my latitude I know how high to point the camera and be guaranteed to get a circle in the view.
  10. I do not need to know what constellations will be visible in the direction I will shoot.
  11. Two major meteor showers (the Perseids and Quadrantids) and 3 periodic meteor showers (the Giacobinids or Draconids, the Ursids and the Andromedids) are well placed in the northern sky.

The Disadvantages

There are a few detriments to pointing north, however:

  • Not every situation lends itself to a view from the south.
  • It takes a longer exposure to form a pleasing arc.
  • To get a circular arc, I must include at least 10 degrees or so above and below the North Star. The farther north you are, the higher in the sky the center of rotation. Those at more northerly latitudes will be more constrained in their choices.
  • The altitude (degrees above the horizon) of the north celestial pole may constrain the choice of lenses to very wide-angle – and may force you to use portrait mode. Or you can create your exposure by stitching together foreground and sky shots.

Another Northern View

Grand View [C_009613-686br]

Looking North from Grandview Campground, White Mountains, Bishop, California.  Shot at ISO 800, f/3.2 for 6 minutes each. Began at 10:11 PM and ended at 5:35 AM. That is 75 shots x 6 minutes = seven and a half hours. Grandview is at latitude 37 degrees North, so the center of the circular pattern is 37 degrees above the horizon.

What About OTHER Directions?

Southern View

Woosh

Woosh: 19 images. Each image: 6 minutes, ISO 800, f/3.2, Canon 5D Mark II, 16mm; Patriarch Grove, White Mountain, California

Eastern View

Valley of Stars (Remix) *Explored*

Western View

Stars and Stripes [5_065561-626li]
Granite Park - 53 Minutes (edited)

Notes

Contrary to popular belief, Polaris, the North Star, is not the brightest star in the sky. Sirius is the brightest star. The brightest objects in the night sky are the moon, and the planets Venus, Mars, Jupiter and Saturn. Also while Polaris is quite NEAR to the North Celestial Pole, it’s not exactly there so even Polaris will make a trail.

This is a reissue of an article originally written in October 11, 2010; Thoroughly revised and updated.

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).