Category Archives: Noise Reduction

The 5 Most Used Photo Enhancement Techniques – Part 2

You are back! Good. In the last article we talked about White Balance and Noise Reduction. As two of the five most useful tools in the arsenal of the night photographer.

In this article we will tackle two of the remaining items:

  • Exposure and Contrast enhancement
  • Sharpening (and de-sharpening)

Healing and cloning will be in Part 3.

While we have seem some fascinating composite and highly edited images our goal is usually to make a compelling photo. But we do like realism, too. So while we will show techniques that can be pushed to extremes to make gaudy Milky Ways, or super saturated star trails, we personally do not go there often.

Exposure and Contrast Enhancement

Below is the result we want to achieve.

640_4

Single Exposure with exposure and contrast adjustments, healing, cloning, selective blurring and sharpening.

But we will be starting with a single daylight exposure from the Outer Banks, North Carolina. When we shot the scene we shot a bracketed exposure at one-stop intervals. Before we look at the exposures, let’s look at the histograms from each of the three exposures

RodantheHistograms

Which one is the best image to start with to make our adjustments? Hint, it’s the one at the right. The +1 exposure has no loss of detail because nothing has been over exposed.  Here is the exposure.

+1 Exposure

+1 Exposure

The scene seems flat and lifeless – almost nothing like it looked to the eye, and not close to what we hope it will be. Part of the reason it looks so flat is that we have not done any adjustments to the original RAW file. If you shoot JPGs the curves and saturation adjustments are automatically applied so you might conclude that RAW images are a waste of time. That would be wrong. The truth is there is much room for improvement in the RAW images and much of the “good stuff” is lost when the camera applies the conversion to JPEG.

All of the histograms show decently exposed images. But it looks like even in the +1 image we still have some room left. That is, we could have exposed a bit more to get the whites all the way to the right.  All of our histograms show that we have no black (nothing at the left edge), and no white (content at the right edge).  An underexposed image might have richer color but it will suffer when we boost the exposure and contrast. The lighter exposure will suffer much less degradation. In fact, the act of reducing exposure deepens the saturation – we do not have to play with the saturation sliders at all!  Pleasing saturation shifts from adjusting exposure are one of the many good reasons why exposing to the right (ETTR) is an effective strategy.

Adjusting Exposure and Contrast – Lightroom Auto

There are many ways to adjust contrast and surprisingly the “Contrast” slider is not usually the most effective way. Using contrast alone often makes the lights too light and the darks too dark. One thing you can try is to use the “Auto” button. It sometimes works. In fact, for these images, it works pretty well with the +1 exposure, but not as well with the normal exposure.

The "Auto" feature of Lightroom under Basic settings

The “Auto” feature of Lightroom under Basic settings

Here is what Auto did for this image:

Lightroom Auto Adjustment

Lightroom Auto Adjustment

The histogram has been stretched and the image looks pretty good. Note that we’ve turned on the clipping indicators by clicking where the white arrows point. After Auto we found a few small spots where black level clipping has occurred as indicated by blue blobs which are circled in red above. No big deal. You can also see what Basic adjustments Lightroom made – exposure has been reduced by one stop, contrast +20, whites +62, blacks -50.  We now have an idea what the Basic adjustments can do. Auto almost never creates a good result when working with dark or night images.

Adjusting Exposure and Contrast – Lightroom Tone Curve

There is another way, and in our opinion, a more powerful way to adjust the exposure and contrast and that is using the Tone Curve. One reason we prefer this method is that it has an almost exact analog in Photoshop (Curves), as well as an almost identical behavior if using Adobe Camera RAW.

Lightroom Tone Curve

Lightroom Tone Curve

What we want to do is to darken the shadows and midtones and slightly lighten the bright areas without losing information – that is to adjust the exposure and contrast. The process is called “stretching the histogram”.  It’s pretty straight forward. Click points on the curve and drag up or down and left or right to create a new curve while paying attention to both the image and the resulting histogram.

Before and After Tone Curve Adjustment

Before and After Tone Curve Adjustment

Can you make these adjustments using Adobe Camera RAW? Yes! The controls are nearly identical.

This is now a good starting point to apply some additional pop, But what if you wanted to do this in Photoshop?

Photoshop Exposure and Contrast using Curves Adjustment Layer

Histogram Stretch using Photoshop

Histogram Stretch using Photoshop

The image above has brought out a bit of pink in the sky, but the dune is a little flat and a little dark. The good news is there is a way to give specific colors special attention – using what we call the “twiddle finger”. You click the hand icon, then pick an area of the image you would like to brighten or darken. The luminosity selected is shown on the graph, then you drag the mouse up or down.

Twiddle Hand curve adjustment

Before Twiddle Hand curve adjustment

 

After twiddling.

After twiddling upward a bit

The twiddling can be repeated. Beware, though, twiddling is global, not local. In general the tone curve should always be flat or upward as you move left to right otherwise you will be lightening dark areas to the point where they become lighter than adjacent light areas.  One way to improve your curve is to smooth the graph. Click the pencil icon then the icon below it (graph adjust), then click the graph (above the pencil).

After a bit more fiddling and twiddling we get what you see below. What more fiddling? Well, we like to add another adjustment curve and select the “Increased Contrast” option.  If things were close to good to start with, the curve might go too far, so adjusting the layer opacity downward is the solution.  In fact, we use the “Adjust contrast curve” so often that we created an action for it and assigned it its own hot key (F9).

640_2

Original Exposure Contrast Enhanced, Histogram Stretched, fully twiddled 🙂

Now we have quite a bit more drama, and much more contrast.  Where are the distractions? What leads your eye away from the interesting parts of the scene?  What are the interesting parts of the scene? Now is a good time to make note of the distractions, because soon we will conquer those.

In truth, we have one more thing to address in the exposure category. The sky is a bit too bright. The solution is to apply a gradient using either Adobe Camera RAW or Lightroom (it can be done in Photoshop but it is harder than it should be, and less convenient).

Graduated Skies – Lightroom

The graduated filter (M) is our friend for not only darkening the sky, but also making other adjustments. That you can make multiple adjustments simultaneously is one thing that sets it apart from the Photoshop methods. Here we have zoomed to 100% to show both a portion of the sky and the location of the graduated filter tool. Note that the sky is a bit “gritty”. We will fix that!

Graduated Filter tool and gritty sky

Graduated Filter tool and gritty sky at 100%

Our sky fix will illustrate one of our other techniques: selective sharpening – only in this case we will de-sharpen to remove the “grit” as follows.

Applying a Gradient to the Sky

Applying a Gradient to the Sky

We use a sky gradient so often that we created a pre-set for it.  The preset reduces exposure by -0.76, contrast by -17, saturation by -24, sharpness by -40, and noise by +100.  Those last two, decreasing sharpness and increasing noise processing result intentionally in blurring. In this case the exposure correction is a bit too strong, but that is easy to fix by bumping the exposure up a little (-0.51).

Let’s look at what this gradient did to our sky. Notice how the grit is just about gone.

gs_2014-02-08_122146

 

If you are thinking that applying a gradient to darken the sky is somehow dishonest, then please don’t use a graduated neutral density filter (GND) which does the same thing at image capture time – but a physical GND does so less elegantly!

Sharpening and Desharpening

We snuck in a trick to desharpen a mottled/gritty sky above, so please read that for one direction. In fact, we find that using noise reduction is often the most effective way to soften because the result – if not pushed to an extreme – is often more satisfying than using any other method. But some things need a little sharpening, like the eyes and hair of people, the boundaries between objects in a landscape.  When we want to do sharpening we never (ok, almost never) do global sharpening.  One reason we do not globally sharpen is it tends to make mottle things more mottled – like the gritty sky we showed earlier.  It seldom makes sense to sharpen clouds or things that are not sharp by their nature.

Indeed in our beach scene there is really nothing that demands sharpening, but all the same, we’ll apply a little bit at the sky/ground border – mostly to help the sea oats stand out a little more. It’s tempting to think that the Lightroom adjustment brush “sharpen” tool is the right one to use here, but often sharpen alone is not as effective. When sharpening is overused it creates odd artifacts. Often the more effective way to sharpen is to use a bit of “clarity” as well as sharpening. Clarity is a local contrast adjustment which has no analog in Photoshop. If you want to use clarity in Photoshop you must bounce over into Adobe Camera RAW. In Photoshop CC you can get a layer into ACR using the Filter -> Camera Raw Filter dialog. Lightroom and ACR are very similar, so lets show ACR here.

Adjustment Brush in Adobe Camera RAW

Adjustment Brush in Adobe Camera RAW

After setting all the adjustments to zero (easy in Lightroom, just double click on each item), we set the Clarity up (+15), and the Sharpness up (+6). Adjust the size, feathering, density and flow of the brush and paint along the horizon and through the grasses.  It’s always better to go a little at a time than to try to go all at once.  When done hit apply or Open.

In Photoshop we often take a completely different approach. Instead we duplicate the layer, label it “Sharpened” then sharpen (using the smart sharpen filter) or noise reduce the entire layer and then mask it all off. We then “paint back in” the areas we want a correction applied to using a white brush on the mask.

Wow. We’ve spent quite a lot of time talking about exposure enhancements and sharpening and desharpening, so spot removal (cloning, healing and cropping) will appear in part 3.

The 5 Most Used Photo Enhancement Techniques

We have been watching ourselves over our shoulders – yeah, kinda weird, right? Our goal is to figure out what it is we do the most to fix and beautify our photography – night photography in particular.  We cover nearly all of these topics in greater detail in each of our NP150 – Photo Manipulation Webinars but we will hit the highlights here. So what are the 5 most used “tricks”?

  1. White Balance / Color correction
  2. Noise Reduction
  3. Exposure and Contrast enhancement
  4. Sharpening (and de-sharpening)
  5. Healing and Cloning

The first two topics are tackled below. The next two in the following article.  Healing and cloning will get it’s own short article.

First to be clear our goal is usually to make a compelling photo, not merely to represent reality. We do prefer realistic over bizarre, but we are not opposed to removing telephone wires and other distractions.  We DO prefer natural looking scenes and eschew the over-the-top contrast and color saturation that seems to be the rage these days.

White Balance

We hate to be the first to break the news, but your camera is pretty clueless about what color white is. The camera will take its best guess. Our experience with night photography is that the camera choice is usually wrong – or at least unappealing. At its core white balance requires adjusting the red, green, and blue colors so that an area that should have a neutral gray or white color is actually gray – not tinged red, blue or green. When shooting at night, understand that every light in the scene – including stars – has a different color bias (tint). Sodium vapor lights for example are horrendous. Sodium vapor lights used in many streetlights are predominately yellow-brown and almost monochromatic. Under sodium vapor lights it will be impossible to achieve a natural color spectrum. You may want to adjust different parts of a night image separately.  You may have to compromise and have a scene that has a bias of a pleasing kind rather than the ugly variety.

Correcting White Balance

The easiest way to make the adjustment in Lightroom or Adobe Camera Raw is with the White Balance tool.  It looks like an eye dropper. You click the tool, then click a gray area of the photo – if there is something that should be gray in the photo, that is. Even a white area is fine (but not an overexposed white). Stars are generally not good choices for gray-scale selection both because they are often over exposed and because many of them are NOT white! In the example below you see a photo of the Ocracoke Lighthouse which is definitely white, not the orange that resulted from sodium vapor lights.

LR_WhiteBalanceExample

The White Balance tool in Adobe Lightroom

ACR_WBtool

Adobe Camera Raw White Balance Tool

The dubious result of getting the lighthouse to its proper color via the white balance tool appears below. The sky and stars are unnaturally and artificially blue.  There are several solutions to this problem: color correct the lighthouse separately or compromise by warming (increasing the temperature) of the selected balance. Or try again by clicking elsewhere!

LR_WhiteBalanceExample_After

By selecting a different location for the gray sample tool a better compromise can be achieved as shown in the photo below. An examination of the scene reveals that the lighthouse is directly lit while the shed (near the bottom of the shot) is not. The shed and other areas in shadow are lit by ambient light reflected from many sources – including sky glow. After selecting the shadow area the remaining white imbalance of the lighthouse can be handled by desaturating using the local adjustment brush – or leave it like it is.

LR_WB_ChoiceB

 

White Balance Correction in Photoshop

The same eyedropper style adjustment can be found in Photoshop, but you’ll have to hunt for it because the “Color Balance” Adjustment is not where you’ll find it!

PhotoshopWB_a

White Balance (gray point) selector of Curves in Photoshop

White Balance (gray point) selector of Curves in Photoshop. The gray point selector is also in the Levels adjustment.

Note that in Photoshop you have two ways to go: use an adjustment layer, or use an Image -> Adjustments -> Curves (or Levels). We recommend using an Adjustment Layer because you can paint on the mask to control the effect and that makes it easy to adjust different parts of the image separately.  To adjust areas separately in Lightroom, use the Local Correction brush and adjust the white balance slider.

Selective Color Balance Correction

Consider the following photo. With the new flight rules, you can use your camera while the plane is taking off or landing.  Here the plane is landing at San Jose International Airport. There are two things about it that are good candidates for fixing. The first is the distracting glare of reflection from light inside the airplane (that’s due to Virgin America’s “Purple Ambiance”).  We’d like to get rid of the distraction and it’s clear we will not be able to simply crop it out without giving up some of the interesting details.

Landing

Glare from internal reflections leaves a blue cast. There is also noise in this one second, ISO 1600 exposure.

The second thing that is noticeable in the 100% (Zoomed view) is the colorful noise in the dark (and light) areas of the photo.  No sky has grit in it – at least not like that!

gs_2014-01-28_085553

100% View of the noise near the wing.

We can tackle both problems separately or at once.  Selectively desaturating, and slightly darkening the blue glare is simple in Lightroom.  Select the adjustment brush (it looks like a face powder brush right below the “Histogram”), dial down the saturation, and slightly dial back the exposure. Then paint on the image where we want the change to occur.  It may be useful to adjust the brush size, density and feathering. Here some feathering is important. We will not try to also increase the noise processing here, because the whole image needs some despeckling.

Below the mask shows where we painted – and not particularly carefully, either!  The Saturation was turned down to -69, and the exposure by almost a full stop. In a brighter sky we might not have been able to darken the touched up area as aggressively.

Attacking the Glare with Local Adjustments in Lightroom

Attacking the Glare with Local Adjustments in Lightroom

The next thing we want to address is the noise. It’s everywhere in this photo. As we will learn in the next article, we often use noise reduction for smoothing things like blue (or dark) skies and in shadows where you would not expect to find details.  Using Adobe Camera Raw for saturation, exposure and noise reduction works the same way as in Lightroom it’s just that the adjustment brush is shaped differently and found in a different place.

The adjustment brush in Adobe Camera Raw

The adjustment brush in Adobe Camera Raw

Out Darn Noise

In Lightroom (and Adobe Camera Raw), there are two simple – and effective ways – to reduce noise in photos. One is to selectively reduce noise using the “Noise” slider of the adjustment brush as we saw with our selective saturation adjustment. Moving the Noise slider to the right increases the amount of noise reduction but does not give you control over what KIND of noise reduction is performed. ACR and Lightroom have specific controls to reduce Luminance noise (dark and light speckles) and Color or Chroma noise (colored speckles). The noise reduction slider with the Local Correction brush does not let you control which type of noise reduction is applied. Sometimes correcting only the luminance noise is the best approach.  Both methods of correcting noise result in some blurring of the photo. How much blurring depends on how severely the sliders are adjusted. There is no formula for getting noise reduction to work well except to be careful not to over do it!  Surprisingly, a little bit of noise makes a better photo. Indeed, there is an option to ADD noise in the “Effects” panel (called Grain). One thing to beware of: using the color noise reduction aggressively will result in loss of star colors in your night sky. In the examples below we’ve brightened the image to make the changes easier to see.

Before any Adjustment

Before any Adjustment, Turning off the default sharpness enhancement.

The noise reduction portion of Lightroom is found in the Details section. Any controls used in this section will apply to the entire image – which is one reason adjustments should be made carefully and deliberately.  The first step we usually take is to eliminate the default sharpening that Lightroom wants to apply.  We would rather selectively sharpen what needs sharpening than doing indiscriminate global sharpening. Next zoom in to 1:1 view of an area (Z key) where noise reduction is needed. For this pick a dark area where some details should be observable. It is also helpful to pick a dark area adjacent to a lighter area where sharpness is desired so the effect of noise reduction can be seen on two elements at once.

We slowly bump up the luminance until we see less “grit”.  Be sure to wait long enough to see the changes made in the image.  We do not generally notice much difference with the detail and contrast sliders, but if we find ourselves adjusting as far as halfway on luminance and not getting what we want, we play with those sub-sliders.

If we still have not achieved the correction we want, we bump the color slider as well… only much more carefully. If there is a LOT of color noise the color noise correction may be the slider to bump first.  Once things are “almost” where we think they look right we choose another area to take a look. It  is important to select an area of the photo that did not need much adjustment – usually a bright area. If the brighter area has become too blurred, we back off on the overall adjustment and then use a local adjustment to add still more noise reduction selectively.

All adjustments made - note that perfect smoothness is not a goal.

All adjustments made – note that perfect smoothness is not the goal!

In Photoshop there are many more ways to reduce noise than those provided in Lightroom and Adobe Camera Raw. Our experience is that the noise controls in ACR and Lightroom are very good – better than any specific filters you will find in Photoshop.  We do use Topaz Lab’s DeNoise photoshop plugin quite a lot however.  The best noise reduction method – when possible is to use the Simple Astrophotography Processing Technique. A photo like the one shown here is not a candidate, however, because that Astro technique requires multiple frames of the same image – that wasn’t possible here with the aircraft coming in for its bumpy landing.

Finished Image

Finished Image

In the next article we will take on the remaining subjects, but you may have already figured out one of the techniques we use for desharpening – aggressive noise reduction!

Star Trail Creation – Step By Step

Originally Published: November 19, 2012
Last Revised: March 3, 2017

I dredged this one up out of the archives. Many people ask me “how do you do those star trails, Steven.”  If you want a grand overview of the process, my Treatise on Star Trails is a good read. However here I reveal step-by-step how I create a star trail image from the first shots to the finished image. The method shown below is for creating simple (lighten mode) star trails. If you want to do some fancy effects, please take a look at our Advanced Stacker Plus.

Here we go.

South Side [C_009842-75br]

Photo 1: Quickly stacked image which is a composite of thirty-three 6-minute 500 ISO exposures and one 30 second, ISO 2000 exposure.

The above is my first quick attempt at creating a star trail, and following is summary of how I created it.

It starts with the test image and continues with the exposure set. For background on how to navigate the various shooting choices, see: the summary Stacker’s Checklist. The theory about selecting exposures may help.  And there is a two-part series that addresses the difficulties you may encounter. See Part 1 and Part 2. If you’re curious how I get the stars to form circles, this article will provide the information.

I usually start with a short (30 second or less), high ISO exposure to gauge several things: 1. How well framed my subject is, 2. How sharp the focus is, and 3. What I may need to adjust to control the sky-glow.

Photo 2: First, image: ISO 2000, f/2.8, 30 seconds.

After taking the first image, I realized two things: one is that the trucks passing were providing helpful light on my foreground – but not always illuminating the entire thing.  The other is that the exposure (ISO 2000, f/2.8, 30 seconds) was under exposed.  I needed to at least double the exposure to 1 minute. Let me stop for a moment. Those of you who don’t do much night photography are thinking “Whoa from 30 seconds to 1 minute is a huge difference.”  But no, it’s not. It’s only one f-stop. It is no different from changing a daylight exposure from 1/200 of a second to 1/100 of a second.

Starting with an exposure at 1 minute, 2000 ISO f/2.8 as a starting point I calculated an  ISO 500, 6 minute exposures at f/3.5. Here is how: A 1 minute exposure at ISO 2000 is equivalent to a 4 minute exposure at ISO 500 (500 is 1/4 of 2000).  Changing the aperture from f/2.8 to f/3.5 drops the light by about 33%, so I increased the exposure from 4 to 6 minutes.

I set my camera to record in RAW and my interval timer to take 5 minute, 59 second exposures every 6 minutes. I pulled out my reclining beach chair, a sleeping bag and slept while the camera clicked.  Below are a few of the shots. Note how the light changes from passing trucks!  You can also see the counter-clockwise rotation of the Milky Way. The last shot was taken as twilight approached is too bright to use because the sky is losing contrast and the light on the cliff is looking flat. I did not include that last shot in the stack.

Photo 3: Collage of some of the photos used in the stack.

I downloaded all the images from my card to my Incoming folder which is organized by date.  I used Digital Photo Professional to pull up the images, applied a bit of contrast enhancement, a slight exposure increase (1/3 of an f-stop), and a very slight noise control over the entire image. I exported in Landscape style which adds a slight saturation increase (Photoshop Saturation and Vividness) and modest sharpening. I cloned the recipe to all the photos and exported them into a “RedRockEast” folder in a temporary directory.  I could have done all these things with ACR (Adobe Camera Raw) or Lightroom.  In this case I didn’t have to do any white balance adjustments because I had preset the camera to approximately 4100K.

I then dragged and dropped all the exported (JPG) images onto Image Stacker which took about 3 seconds per image – less than two minutes to create a result. My option for Image Stacker was “Brighten” mode. I could have used the Star Circle Academy Stacking Action in Photoshop instead and the result would have been identical.  The stacking action takes about the same amount of time, but is more versatile and can even use raw images. (Note: StarStax is a program that supports Mac, Unix and Windows and works well, too!)

Photo 4: First Results stacking 34 images in Image Stacker by Tawbaware – this is effectively a 3 hour, 24 minute exposure.

The result was a little dark and flat so I used Picasa 3 to increase the exposure (called Fill Light), highlights and shadows – each by about 1/4 of the scale, and I warmed the photo by slightly tweaking the white balance (Color Temperature). That was all I needed to get the image shown in Photo 1.

Screen Shot 1: Picasa Adjustments

One obvious problem with the result is that the combination of the early short exposure with the sequence of shots left a gap. There really was no reason to include the first shot.

I want the cliff to pop a bit better, so my next course of action was to work on improving the foreground.  I found all the brightest shots of the cliff face (e.g. when the trucks were lighting them), and combined them using additive stacking to brighten them and averaging to reduce the noise. Remember that “brighten mode” (Lighten in Photoshop) does not brighten anything – what it actually does is select the brightest pixels at each location from each of the images in the stack.  The brightest pixels may also be noise! Using averaging reduces the noise significantly – but it will not remove “hot” pixels; we will address those later.  Fortunately Image Stacker has an option to stack and average. All you need do is specify the divisor.  If you have 10 images and specify a divisor of 10 then you are simply averaging. But if you specify a divisor of, say 5, then you are averaging AND effectively increasing the brightness by about 1 stop.  I used 12 images and a divisor of 3. And I made the same adjustment to the result in Picasa as I showed in Screen Shot 1. But I wasn’t happy with the result – the foreground still wasn’t bright enough.

Next I took 10 of the brightest images and Stacked them (additive).  After tweaking shadows and brightness in Picasa I got this:

Photo 4: Additive stack of 10 images.

Now my foreground is better, but I have created a new problem. The sky is over-bright and the hot pixels and the noise are significant as shown in a 100% crop below.

Screen Shot 2: 100% view showing Hot Pixels and noise (white speckles)

The hot pixels here have a purple fringe to them. Sometimes hot pixels are tinged red, green, blue, white or gray. I will fix hot pixels in my next to last step using the clone stamp (Picasa’s retouch) or the healing brush in Photoshop.

While the noise is obvious at 100% I think it will be fine so I am not going to address it.  If I later find the noise intolerable I will go back and stack more images and average them. Or I may return to the original images and apply stronger noise reduction in Digital Photo Professional and re-export them.

My next task is to remove the over-bright sky from the Photo 4, above. Sky removal is rather easy with the wand selection tool in Photoshop. I select all the sky and fill with black after making a few more tweaks to contrast and color.

Photo 5: Sky removed and replaced with black.

Since I now have a black sky version with the foreground as I like it, I can include this frame in any other stacks I make, and my foreground will be just as I want it. If I were working entirely in Photoshop, I would not have to fill with black, I could just use the result as a layer with only the foreground revealed by a mask.

To complete the process, I restacked 33 images together with the sky-less foreground image (Photo 5). Some more minor shadow and color temperature tweaks and some spot corrections of the few hot pixels (there were about 15), an addition of my copyright and this is the result:

Photo 6: Final Image

Since I had all the images for the stack, I was challenged on Flickr to also make a time-lapse video. This video below also helps to illustrate how stacking works. I collected the original thirty-three 6 minute exposures and cropped them to HD format (1920 x 1080). I then created and a sequence of stacked images using the intermediates option of Star Circle Academy Stacking action and joined them into an animation complete with a lovely snippet of the song Kidstuff by Acoustic Alchemy. In my next column, I’ll show how to create the time-lapse animation.

Red Rock Dancing *Explored 03-03-2011*

If you would like hands on experience and instruction, you can join us at a StarCircleAcademy Workshop

Advanced Star Trail Tricks

Published: Oct 11, 2012
Last Update: April 26, 2016

I have been playing with Star Trail processing for quite a while.  Ever since I wrote the StarCircleAcademy Stacking Action I’ve been tweaking processing to try different things. Sometimes failure is inevitable, sometimes… well, you’ll see.

First, you may want to look back through my earlier columns on shooting and processing star trails because this is not a primer on star trails – it builds on what I’ve previously written and this is not a good place to try to understand what stacking is.

Second, please understand that I use a variety of tools but almost all of my more successful endeavors end up as layers that are combined in Photoshop (CS5 at the moment).  You could combine your layers in GIMP if you don’t have Photoshop, but you’ll be out of luck if you try to use Lightroom.

Here are my star trail effects:

  1. Smoothee – Averaged sky and/or foreground to reduce the grittiness that sometimes results from brighten stacks. I’ve been espousing this for quite a while. See the Simple Astrophotography Processing Technique.
  2. Blobulous – stars at the beginning (or end) of a trail are made to stand out from the rest of the trail.
  3. Comets – star trails appear to grow brighter and the end of the trail looks like the nucleus of a comet.
  4. Streakers – Like comet only the trails are longer
  5. Blackened – A clever trick removes sky glow from light pollution, the moon, or twilight.

And of course you can make “Blobulous Comets” and “Blobulous Streakers” and “Blackened Smoothee Comets” and more.

Building Blocks

To creatively combine exposures, I usually create the following stacked frames.

  • Dark (Darken in Image Stacker/StarStax)
    The darkest elements emerge – especially the hot pixels
  • Brighten (aka lighten) stack
    The Brightest of everything is present, including hot pixel and more noticeable noise
  • Average
    Contrast is reduced, smoothness increased.
  • Additive (called “Stack” in Image Stacker)
    Hot pixels become really bright.
  • Scaled (called Stack/Average in Image Stacker)
    Allows some increase in brightness but more smoothness, too. Experiment with different divisors.

Normally I create all of these combinations using Image Stacker against my JPG files because it is really easy to do.  I end up with a set of frames something like these although I’ve significantly brightened them so that they are easier to see.

Smoothee

In a Nutshell: Combine the Average stack over the Brighten stack using Normal mode at 45% opacity.

I’ll start with the Smoothee technique since it’s probably the easiest to do and perhaps the easiest to understand.  The problem with “Brightness” (or lighten as it’s called in Photoshop) is that it will also pick up all the hot pixels, and the brightest bits of noise.  Averaging on the other hand tends to smooth out everything except for truly hot pixels since most noise is random. By putting an averaged stack as a layer over the brighten stack and then adjusting the blending modes and opacity you get a smoother sky and foreground.  Exactly what settings to use depend on the images, but surprisingly many of the blending modes for the Average layer work here including Darken, Multiply, Overlay, and Normal. The starting place for Opacity is about 45%.

Hint: You can also use an Additive stack instead of the average stack but usually only the Normal blend mode will work.  For even more fun combine the Additive stack and the Average stack.

For additional smoothness you can also subtract the “Darken Stack” while adjusting the opacity to prevent halos and weirdness.

Blobulous

In a Nutshell: Add one of the single frames more than once.

What do “Blobs” look like? Like this…

“Fat Star” processing.

There are two ways to produce “Blobs”. One way is to add “Comets” to a smoothed star trail. The other is to simply pick an image (usually the last one in the set) and add it in using “Add” or “Screen” mode. To make the blob more pronounced duplicate the last frame so it’s added twice. BUT remember when you add in any single image the hot pixels are going to come out… and even more so if you add an image twice.

Comets and Streakers

These two techniques require some fancy stacking techniques. Fortunately I’ve created an action to do all the fancy stuff.  I’ll be rolling out the action and the explanation to my Photo Manipulation Webinar participants first <NOTE: The Advanced Stacker PLUS action has been released and is available for purchase in our store>.

Oh, here is a peak at what the Comet action looks like:

What's The Point?

And here is what an animation of comets might look like:

 

Settings

I know you’re going to ask so let me save you some typing. Except for the “Comet” image above, all images used in these illustrations were taken during the Ancient Bristlecone Pine Workshop in the Patriarch Grove on White Mountain, East of Bishop, California.

The 34 or so images that I’ve combined in the examples above were all taken with the following settings: Canon 50D, ISO 400, f/3.5, 79 seconds, 10-22mm lens at 15mm.