Down with the Noise!

Clouds, Coast and Milky Way (vertorama)

We need to start with a definition.  What is noise?  A reasonable, widely excepted definition is that noise is any artifact or defect that reduces the overall fidelity of an image. But this definition is too broad because defects like glare and chromatic aberration would be included. Glare and chromatic aberration are caused by the optical system, not by the sensor. So a better definition is needed.

Noise Means: Variations in luminance (brightness) and chrominance (color) in an image that are not in the object being imaged and not caused by the optical system. These variations generally are perceived as colored speckles and resemble grain in film photography.

There are, however, many types of noise – each having different causes and thus different solutions.

Astonishing Fact Number 1

Every image has noise!  Indeed, noise often aids in creating sharpness.

Astonishing Fact Number 2

Usually the problem is not noise but with noise that overwhelms the “signal”.

The Five Kinds of Noise

There is not just one kind of noise. There are five. Ok, there are actually MORE than five kinds of noise, but here are the most significant ordered from most to least likely to overwhelm a night image.

  • Random (quantum effect) noise.
  • Fixed pattern noise (banding)
  • Stuck (Hot Pixel) Noise
  • Offset noise
  • Shot Noise – applies to very dim subjects and shadows

You may see different terminology in other articles. For example “Fixed Pattern Noise” is often used to describe stuck/hot pixels.  For me “stuck pixels” while often annoying are one of the easiest to control using “dark frames” – or with newer cameras, require NO work. More on that in a moment.  Let’s briefly address each kind of noise, what causes it, and how to best prevent it.

Random Noise

Despite what you may have been lead to believe, random noise IS random. Speckles can appear anywhere on your image in light or dark areas. These speckles are caused by *random* quantum effects.  Electromagnetic induction, electro magnetic fields, gamma rays, sunspots, static charges, impurities in the electronic substrate, and blind bad luck. ALL of these effects are magnified by heat which is the single nastiest mafioso of noise. Longer exposures produce more noise. And “Dark Frame Subtraction” (an element of Long Exposure Noise Reduction aka LENR) can do *nothing* to alleviate random noise. Soon however we will tell you how to reduce noise the way an astrophotographer does.

Fixed Pattern Noise (e.g. Banding)

The more you push an image, the more likely you are to see vertical or horizontal banding – or both.  Pushing refers to high ISO sensitivity or large increases in exposure in post processing. Pushing also refers to using lower quality sensors at well above their quantum efficiency – which we will explain in a moment.  As with random noise higher ambient temperatures can intensify this type of noise.  Another example of fixed pattern noise refers to pink, purple or overly bright areas in an image. Early cameras were particularly prone to this form of noise because the electronics of the camera were unevenly heating the sensor – and as has been pointed out above, temperature is the enemy of a clean image.

Stuck / Hot Pixels

To be precise, it’s usually not “pixels” that are stuck or hot – it’s sensels. Because each pixel is comprised of two green, one blue and one red sensel it’s often easy to tell which of the sensels is defective by observing the color of the pixel. If red – the red sensel is registering a value higher than it should. “Stuck” sensels usually result from one of the following causes:

  1. Measurement errors in the electronics (e.g. photon collector doesn’t empty properly, current leakage), or an unusually high offset bias.
  2. Physical damage to the filter (lens) over the sensel – usually at manufacturing time.

Often the higher the ISO, the more offensive a stuck pixel appears – however stuck pixels which are present in every frame can be removed using dark frame subtraction, and indeed modern cameras can remove these automatically. Dark frame reduction is something the camera does when it does “Long Exposure Noise Reduction”.  Sometimes resetting the camera can dramatically reduce the hot pixels. The method for resetting a camera varies, but on many Canon cameras, the prescribed method is to use the manual “sensor clean mode” -> Now and leave it in that mode (with no lens attached) for at least a minute before turning off the power.  Also note that heat often exacerbates the stuck pixel problem, too.

Tip 1: “Reset your camera after it has temperature stabilized and before shooting. Usually this is a simple as “Clean Sensor -> Now” Many modern cameras make note of the stuck pixels and will automatically remove them for you!

Offset Noise

The process of measuring each sensel involves an imprecise analog to digital conversion. The measurement phase can introduce its own error called bias. Rather than reading an unexposed (black) sensel as a zero, some sensels may read 2, some 4 and others 7.  This offset noise is also managed pretty well by LENR and except when it is really bad, is not significant.  Merely darkening the darkest pixels may be sufficient to hide offset noise.

Shot Noise

This is a curious name but it refers to the fact that photons (light) do not arrive at a regular rate – especially for dark subjects like dim stars or the darkest of shadows. Since the camera collects and counts photons, variations in the rate of arrival of photons results in speckling. However normally shot noise is minimal and not noticeable. Shot noise is usually noticed only when severely underexposing or by aggressively brightening underexposed areas.

 

Noise Reduction Methods (Pre and Post Shot)
Type of Noise Pre-Shot  Post Processing
Stuck Pixel(s) Cooler, Camera Reset, LENR Dark Frame Subtraction
Random Cooler, Shorter Averaging, DeNoise, ACR
Banding Cooler DeNoise, ACR
Shot Longer Exposure
Offset LENR Dark Frame Subtraction

 

Looking Noise in the Face

Zooming in on a dark frame – one taken with the lens cap on shows the nature of noise. First is a dark frame without any adjustments.  Some red and green noise is barely discernible.

Dark Frame 1 - Linear Mode, Unmodified

Dark Frame 1 – Linear Mode, Unmodified

Looking at the same frame with an adjustment to boost the saturation and brightness, the nature of random noise is more obvious.

Same Single Dark Frame Boosted with curve to show content.

Same Single Dark Frame Boosted with curve to show content.

Notice how the noise is different in the same area of another frame.

DarkFrame2Boosted

For more examples of noise in dark frames, see this article.

Noise Reduction – The Environment

Sadly, one of the most significant sources of noise is heat – the heat in the air.  Shooting in the desert at 100 degrees Farenheit will always create far more noise than shooting at 30 degrees F below zero.  Can you help the problem by cooling the camera? Yes you can!  Gary Honis built a cooler for his camera (used for astrophotography) and got quite impressively better results. His chart of noise pixels is no longer on the site, but it dropped from thousands of bits of noise to to tens by cooling his camera 40 degrees Farenheit. However beware that if you also cool the lens you’re likely to get dew.  And if you have an open system like in Gary’s Telescope scenario, you may get dew on your sensor, too.  Not surprisingly ALL high-end cameras for astrophotography are cooled. The most extreme are cooled with liquid nitrogen!

The second take-away is this:

Tip 2: If possible, opt for shooting in cooler climes.  If you’re shooting the Milky Way, for example, you can check a Planisphere and you’ll find that you can get the same star configuration at different times of the night in different parts of the year.

 

Noise Reduction – A Better Sensor

You may have seen some velvety smooth night images produced by top of the line cameras and may be wondering if you can achieve such results with your middle of the line equipment. Unfortunately the answer is mostly no.  Generally speaking two things dramatically affect the amount of noise produced in a camera’s sensor with regard to night and low-light images and those are:

  • Sensor density: the more sensels you pack into a given amount of space the less light they receive. Set out a thimble and a bathtub in a rainstorm and it will be no surprise to find far less water accumulates in the thimble than the bathtub. The smaller, closely packed sensels in high megapixel crop-factor cameras have a distinct disadvantage over the relatively lower density, larger real-estate full frame cameras.
  • Sensor design: Modern camera sensels are spaced more closely together so they waste less light. They are also more efficient.  Better sensors also have higher “full well” capacities – that is they can count more photons more accurately before filling up or spilling over. Because of better sensor design it is possible for a higher megapixel sensor to outperform a lower megapixel sensor of the same size.

There is one other measure of a sensor that keeps getting better: it’s quantum efficiency.  In an ideal sensor each photon will increase the count of the sensel it strikes by exactly one.  The efficiency of a sensor can be determined by calculating its “ISO at Unity Gain”.  The higher the number, the better the sensor performance.  DxO Mark calculates approximately this value and represents it as the ISO value in its “Sport/Low Light” rating.  For daylight subjects with gadzillions of photons flying a great picture doesn’t require a high efficiency sensor. But in low light every photon should be counted!

Here are the top 3 Full Frame or crop cameras (plus #4, the one I chose) ranked by ISO of the “Sports Score” (a good approximation of the quantum efficiency) and initial price as of November 16, 2017. Click the image to see the latest chart and to find your own camera.

DxO Mark “Sports” Score by Cost

Tip 3: Learn what your camera quantum efficiency is and shoot near or below that ISO level. Selecting a higher ISO than the quantum efficiency magnifies the noise, while a lower ISO tosses out good data.

Noise Reduction – Software

There are many ways to use software to reduce noise in an image. Tools like Canon’s Digital Photo Professional (DPP), Adobe’s Camera Raw (ACR), Lightroom – which uses the ACR component, and many plugins and filters within Photoshop.  Keep in mind that no noise reduction technique will result in keeping a perfectly sharp image – all methods blur the result.  TopazLabs DeNoise (and inFocus) product claim to have deconvolution techniques to keep edges sharp. The good news is that a slightly blurred sky – like clouds, looks quite natural. What is my preferred method?

  1. Ignore it!  That’s right. Many images that appear noisy when pixel peeped are really quite fine for reproduction at reasonable sizes and viewing distances – especially if no overly aggressive brightening or contrast enhancements are done.
  2. Adobe Camera Raw: I use ACR when the noise is fairly low.  ACR does a suprisingly good job of removing noise if you bump the “Luminance” and “Color” Noise reduction sliders to the right and turn down the Luminance Detail and Color Detail sliders. How much depends on the image and how desperate you are to save it.  NOTE: Lightroom’s controls are the same as those in ACR except that you can selectively apply noise reduction which is preferable. Being too aggressive with the Color noise may eliminate your star colors, so beware!
  3. Use a Photoshop Plugin.  There are a kajillion ways to reduce noise within Photoshop – after ACR – including the “Despeckle”, “Dust and Scratches” and “Reduce Noise” filters (and more). But we find that in Photoshop all the built in ways are underwhelming.  I have tried several plugins including DFine (Nik Software), DeNoise (Topaz), and a few others.  The one that wins for me is TopazLabs DeNoise.  Below are samples of the original, and the DeNoised versions.  I think the result speaks for itself.  But note that I *intentionally* used an artificially high ISO to increase the noise.  A better ISO for the Canon 5D II would be about 1600 ISO – a little less than its 1815 rating by DxO Mark Sports score.

C_061861b_orig C_061861b_deband

Here is a closer crop of the areas most changed by the noise reduction:

The original image and two attempts at noise reduction. Notice that some areas (X) remain problematic

A good noise reduction strategy is to NOT denoise everything.  Duplicate the image to another layer in Photoshop. Apply noise reduction to that layer and then use a layer mask to reveal the noise reduction selectively. In the example above, masking off the Topaz Denoise on the tree would have left a sharper tree.

 

Median / Averaging To Reduce Noise

Yet another noise reduction method – useful for random noise is to do median (using Statistics in CS Advanced or Photoshop CC) or averaging of shots.

On the left is a single 25,600 ISO exposure. On the right, 15 shots averaged but with no other noise reduction attempted.

Hopefully you remember that there are many different kinds of noise. The techniques described above are used for controlling both random noise and stuck pixel noise. But stuck pixels can be managed by doing your own “dark frame subtraction“.

 

Resources:

 

Multi Row Panorama Rig

We have many articles on panoramas.

The point of this article is to describe the multi-row panorama apparatus I created with off-the-shelf, inexpensive parts from Amazon. The good news is assembly is pretty simple. When you are done you will have a gimbal style mount suitable for taking multi-row panoramas using a modestly sized camera/lens combination. It is important to point out that you need a sturdy tripod and head beneath as the extra top-heaviness will tax a wimpy head or spindly legged tripod. I use the Gitzo mountaineer series tripod – it is lightweight, stable and has served me well for many years. I also have an older (much heavier) aluminum-legged Manfrotto. I have Acratech ball heads on each tripod. Those Acratech heads are really light, and solid. I HIGHLY recommend them.

Multi-Row Panorama Gear in action at Asilomar State Beach, California

What is a Single-Row Panorama (or Vertorama)

A single row panorama is what you get when you take a series of photos left to right (or right to left) – usually in portrait mode to extend the field of view up to 360 degrees. A vertorama is the same idea, except you usually use landscape mode. In either case, the camera needs to be rotate around the “nodal point” or “no parallax” point. The no parallax point is usually found IN the lens, and is thus never where you attach the camera to a tripod.

What is a “Multi-Row” Panorama?

Imagine taking a single row panorama, then repointing up (or down) and taking another single row panorama. Now you have a multi-row shot.

Here is my parts list all purchased from Amazon.

  1.  $19.99 Neewer 200mm Rail Nodal, Quick Release Clamp  [1]
  2.  $28.99 Koolehaoda 360° Panoramic Head  [2] This unit was chosen because all the other possibilities had very long lead times.
  3.  $16.95 Desmond 200mm DLR-2002
  4.  $39.95 Desmond DVC-220 220mm Rail 90° Arca Compatible w Vertical Clamp instead of this 90 degree rail, you can also buy a regular rail (another #3) and a 90 degree clamp.

Total is about $125 USD and weighs just under 2 pounds.

NOTES:
[1] You can get shorter or longer rails. Might as well get the longer one. While it is heavier, you can use it with a longer lens.

[2] If you have an old tripod head, it may have a panning clamp and/or leveling base that you can re-purpose.

Other Items to Consider

  • $430.00 Acratech GPs-s Ballhead with Clamp Ball Head with Arca Clamp. This one is not required, but it’s really good and has the advantage of being usable without a leveling base by using it “upside down”. And yes, it is designed to be used that way, notice how the markings are repeated so that they are visible right side up, and up side down.
  • ($60-$200) L-Bracket (arca swiss) for your particular camera
  • Leveling base.
  • At minimum you will need a bubble level somewhere on the horizontal surface or a means to align the unit perpendicular to the ground.

Assembly and Alignment

Assembly is straight forward. The only tricky part may be securely mounting the Panoramic clamp to the vertical rail. All the rest go together with the built-on clamps.

What If I Do NOT Have My Ball Head Upside Down?

As we show in the video, we have mounted our Acratech GP-s head “upside down”. This allows us to level what was the base using the ball head and then use the rotation of the base as a horizontal panning clamp.  There are several ways you can proceed if you do not, or cannot use your tripod in this way:

  1. If you already have a panning clamp on the top deck of your ball head, level the deck and use the existing panning clamp.
  2. If your ball head has a panning base, you can carefully align the tripod so that the head mount (the deck where your ball head attaches) is level. Then align the clamp so that it is level as well. You can use the panning  base of your ball head. Note this is not easy to get right, but a slight misalignment is usually easy to correct in the stitched photos.
    NOTE: Be sure to check for level-ness through a complete rotation!  Our Acratech Nomad ball head, for example, is not designed to be easily mounted upside down, and this method is what we use.
  3. If your ball head does NOT have a panning base, then you can buy a second panning clamp and attach that to your ball head clamp (or replace your existing clamp with a panning clamp).  WARNING: Not all panning clamps are easily attached to arbitrary ball heads as there is little standardization

 

Taking and “Stitching” Panoramic Photos

Since we have plenty of material on how to  do this, we will refer you to our prior articles (see the top of this page).


Alternative Hardware

If assembling a multi-row panoramic head from parts is not exciting, there are several pre-built options.

ProMaster GH25K Gimbal Pan Kit

ProMaster GH25K Gimbal Pan Kit

At about  $300 USD, it seems pretty well built. The flaws in the design are:

  • It does not have  a leveling base,
  • While the bottom head (vertical axis) has handy detent stops, the horizontal axis does not.
  • There is no bubble level on the base.

I have not used one, but found and played with one in a local camera store, and saw that is also available online. Like the system we laid out above, do not expect this rig to hold up your 20 pound camera/lens combination. Total weight is about 2 pounds and rated capacity about 7 pounds.

 

Really Right Stuff Multi-Row Pano Package – PG-01 or PG-02 (the Big One)

There are two units. The PG-01 which is similar to what we custom-built above at a price of $285 USD (at B&H). The other option is a beast. And at $795 USD (from B&H) is not cheap, nor complete. You may still need a leveling base. There are many options available, too, including a gimbal cradle. Check out the possible configurations at the Really Right Stuff website (though when we last checked the units were on back-order).

PG-01 for smaller cameras (non telephoto lenses)

You will also need a nodal rail to pair with the above. There are no detent stops for this, and as with others, you’ll need to level your base to use this.  (There is also an option that includes a leveling base for about $290). One reviewer reported that he had trouble keeping his moderately heavy camera from slouching down on the vertical arm. There does not appear to be a bubble level on the horizontal bar as there is on the larger model.  The version with the built-in leveling base clearly does have a bubble level. There are no detents to set up fixed rotational amounts. Note that the vertical rotational axis clamp is located under where your camera would be and might be inconveniently located.Total weight is about 1.3 pounds with the two pieces plus a nodal rail.

 

The Really Right Stuff PG-02 Panorama Kit (from B&H)

 

As with all Really Right Stuff gear, there is some seriously thoughtful design and overbuilding here. It is beefy with big easy to find knobs, great clamps and little touches like the target on the center of the rotational axis. Why is that a good idea? If you align the bulls-eye target in the center of your image (see our video), you have the correct location for multi-row panoramas (provided the set back is correct). You may still need a leveling base (though might be able to use the bubble level at the right edge). You can replace your current head with this unit and have full mobility, otherwise you’ll need a plate to mount the unit to your ball head.  All that great design costs money though: about $795 and up. Weight is about 3.3 pounds.

Lickety Stitcher in Lightroom + Panoramas IN Lightroom

Pointyland Redux

A conventional panorama stitched with Microsoft Image Composite Editor from 3 images.

Maybe we should start by explaining Lickety Split. Lickety Split is US English slang for fast so “Lickety Stitcher” is our contrived slang for a fast image stitcher. Image stitching is what you do to create a large image out of several smaller, overlapping images.

We’ve reported how much we like the FREE Microsoft Image Composite Editor (aka ICE) for stitching images because it is faster and more accurate than Photoshop’s Photomerge or Lightroom’s new, but sometimes anemic Photomerge. Here is a simple “quick panorama” method of creating a panorama from about 3 clicks. How? Configure Lightroom to run ICE as an export step. After creating the export step (described below) you do the following:

  1. Select photos,
  2. right click “Export -> ICE Quick Stitch”
  3. Click through the ICE Menus to Stitch, crop and Save.

Sadly, there is no Image Composite Editor for Mac computers. If someone knows of an equally easy to use, fast version for the Mac, let us know in the comments!

How To Set Up Lickety Stitcher

To use Microsoft ICE (or PT GUI, or other external tool), you create an Export setting for it. Click a photo (any photo), then “Export” and Add new settings as shown below. The only tricky part is finding the program you want Lightroom to run. In Windows it has to be the actual path, not a shortcut.

Microsoft ICE Panoramas from Lightroom

You don’t have to settle for only a “quick stitch” (which is best done with JPGs), you can also export full sized TIFF files and stitch those.  ICE can save documents in Photoshop .psd format and others. And if you have another image stitcher you really like, e.g. PT GUI, you can probably use this same trick to make that software work on demand.

What About Lightroom for Stitching?

We were happy to discover that Lightroom and Photoshop image stitching (panorama) creation has improved quite a lot since our first disasters trying to do vertoramas and panoramas. Indeed, I think we would be happy to use the new tools and skip using ICE in many circumstances. Here is how you use the Panorama creation feature of Lightroom.

First, pick your images. They should overlap by at least 1/3 from frame to frame. And you can pre-process them with noise removal and such. Highly recommend you do at least two things to images before you try to stitch them:

  • Use vignette correction appropriate for your lens.
  • Consider using Distortion correction before creating your panorama – not always necessary.

Then right click and find “Photo Merge -> Panorama”.

Lightroom did a quite respectable job. We were able to to create the image below entirely in Lightroom. We did see some problems, however:

  1. We got a message about “unable to save metadata”
  2. Lightroom insists on creating the image as a .dng file and uses the name of one of the files you picked (we’d like it to be a mash of first-through-last.
  3. Lightroom didn’t seem to be as smart as ICE in how it stitched the images. ICE joined the images without the airplane and satellite trails, or maybe it was just better at blending them out. We had to do that work by hand on the image Lightroom created. It was not difficult, though. It is not the first time we have seen ICE handle an image better than Photoshop PhotoMerge

In ICE we manually  bent the slightly arching shot back into vertical form and did manual cropping. In Lightroom we used the Boundary Warp option at the end to make the images fill the frame nicely. Here is what we got from those 11 images:

10 Image Panorama using Only Lightroom Photomerge

You can compare the above to the same images used via Microsoft ICE and finished in Photoshop.

Overarching Majesty

Stitched in ICE, Finished in Photoshop

Multi-Row Panorama

Here is a more ambitious 22 photo, multi-row panorama stitched with Microsoft ICE. There was a stitching problem due to cloud movement… maybe you’ve spotted it.

Asylum at the Sea

 

Stitching Software Alternatives to Photoshop, Lightroom and ICE

  • Hugin (FREE: mac, PC, Linux). Don’t much like this one even though it is free.
  • PTGUI (mac, PC). A little clunky, but does much more than stitching including HDR and can be automated. This is the one tool you need when you need to convince an image to stitch that just won’t do it. It can’t do miracles, but with work, it can get the job done.
  • Others… that we don’t have familiarity with, though we have heard good things about Kolor Autopano

Adding Special Touches to Your Astro Landscape

1000 ISO, f/2, 3 minute exposure with some augmented stars

Because stars are pinpoints of light, the camera does not capture them as our eyes see them. To our eyes, brighter stars stand out more noticeably than dimmer ones. At a workshop in Alabama Hills, one of the participants, Julian Köpke, was using a diffusion filter so the stars captured would look more like you see with the naked eye. Sometimes nature provides its own diffusion filter in the form of high, thin cirrus clouds as shown below. The large bright orb is the star Sirius in the constellation Canus Major (Big Dog). The orange star near the top of the frame is Betelgeuse in the constellation Orion. One nice thing about the blur that the clouds added is the star color is more noticeable. But the diffusion here is not uniform because the belt stars (Alnitak, Alnilam and Mintaka) and “corner” stars (Bellatrix, Rigel, Saiph) in Orion are all noticeably brighter than the surrounding stars while in this photo only Betelgeuse and Rigel stand out.

Dog Star [C_065586]

You can create a make-shift diffusion filter by shooting through a nylon stocking – or buy a diffusion filter. The disadvantages of using a filter are that everything is blurred – including the foreground and you reduce the amount of light collected. Most night sky photographers try to avoid clouds and you will get an image like this:

The moon and Teapot Asterism in Sagittarius – over Lone Pine Peak – as shot.

When what you had in mind is something like this:

Same Photo as above, but with the Teapot Asterism in Sagittarius enhanced.

How to Bring Out Star Color And Enhance The Apparent Star Size

Our Advanced Stacker Plus has two built-in ways to increase star brightness. We call those Bump Up and Pump Up the stars. Bump Up creates a small blur by literally duplicating the shot , nudging the duplicate(s) and recombining .  Pump Up is more sophisticated and tries to find the stars so it can then apply enhancements to just the stars. But there is a new tool in the arsenal that I have begun using: Star Spikes Pro from ProDigital Software.  Version 4 is the latest as of this writing.

NOTE: Star Spikes Pro and HLVG described later are currently only available on Windows machines.

You can use the Star Spikes Pro plugin to add diffraction spikes and diffusion. The most common diffraction spikes you see with stars are due to obstructions in the telescope used to photograph them and many people come to think of the spikes as evidence of astrophotography.  You can create diffraction spikes easily on your own.- just stop down your aperture;  however stopping down to make stars create those spikes will not work well.

The first time I tried to use Star Spikes Pro it did not quite work as I expected.

Look hard. Star Spikes Pro decided the moon was a huge star outclassing all others.

Indeed it took me a bit to realize what was going on. The good news is it was easy to work around. The huge moon looks like a huge star to Star Spikes Pro – and that makes perfect sense since the plugin is usually used with Astrophotography that does not involve landscapes.

Here is how I made it work as I wanted and limited the effect to just the desired stars.

Layer Palette and Steps to Enhance The Teapot Asterism

Above left is the layer palette. Look carefully and you may spot the fix. After loading the image (1) I first duplicated the original and called the new layer Heal (2). I then did minor contrast adjustments, used the healing brush to remove hot pixels and other offenses (short satellite trail). Next I duplicated the Heal to another layer (3) and fed it into Hasta La Vista Green – a free plugin written by Rogelio Bernal Andreo of DeepSkyColors. HLVG removes green which is an unnatural sky color usually caused by RGB artifacts. HLVG operates on the entire layer and does not know the difference between land and sky. To leave the natural green in my landscape I used the quick selection tool, dragged it across the sky followed by Select -> Modify -> Expand 4 pixels. Then I created a Layer Mask using “Reveal Selection” (4). That made the foreground come back to its normal state. If you look carefully you will notice I also used a white brush to add some of that green removal back onto the mountain by painting on the HLVG layer mask (4).

The next operation was a finger twisting sequence that has no menu equivalent: Ctrl-Alt-Shift-E (on Mac that’s Command-Option-Shift-E). What that sequence does is “flatten” all the visible layers and create a NEW layer in the process (5). That layer I called Input to SSP.  Since I had discovered that Star Spikes Pro was confused by the moon (and could be confused by the foreground), I used the quick selection tool again and brushed it across the foreground. By default using the quick select tool again ADDs to the current selection so I brushed it around inside the moon and its halo. At this point I did not need to create another layer (Ctrl-J/Command-J or Duplicate Layer) but I did so that it was easy to see what happens next. After creating the new layer I selected it and used the delete key. Delete removes the selection making it transparent – that is the foreground and moon were now gone (6).

Next up: let Star Spikes Pro loose on the image. First deselect (Ctrl-D Command-D) or Select -> Deselect), and feed the sky layer to Star Spikes Pro via Filter -> ProDigital Software -> Star Spikes Pro.  The defaults for SSP produced the image below (I’ve zoomed in on the teapot asterism)

I felt the color was a bit too strong, and I did not want the diffraction spikes. The next step was to select “Advanced” – just below Settings, set the Primary quantity to zero. Next was the Secondary tab where I reduced the quantity to 44, the intensity I bumped up to 23. Soft flare I set quantity to 12, bumped up the intensity, dialed down the size a little and dialed down the Hue to -21. These adjustments were all based on eyeballing the image and were made for aesthetic appeal.  After all the adjustments looked about right, I saved the settings as a new adjustment I called “DiffusionOnly”. Finally I clicked OK and my layer was all nicely done by the SSP filter.

The filter processed a few more stars than I intended to augment. The simple solution was to create a “Reveal All Layer Mask”, select a brush, the color black and paint out all the effects I did not want on the layer mask (7).

The final operation was to use an Adjustment Layer (8) to increase the contrast and restrict that adjustment to the sky (where you see white) and tone the adjustment down a little with a low-flow back brush on one area that looked a little too dark.

The topmost layer in the layer palette is my watermark.

There Is An Easier Way!

With some experimentation, and some coaching from the plugin author I discovered that Star Spikes Pro has several features that make the process easier than I imagined. Instead of creating the transparency (deleting the moon and landscape) I only needed to select the area I wanted Star Spikes Pro to operate on.

Also, instead of masking off the stars I did not want affected after the fact, Star Spikes Pro has two tools to greatly simplify things the: “Hide” tool to turn off any effect that I did not want, and the “Show” tool to turn the effect on.

 

Star Spikes Pro limited to specific section of the sky via a selection and using the Hide tool to turn off an effect.

 

The net is that you can get that nice diffusion effect for your stars without having to compromise by shooting through a diffusion filter. However if you DO want to try a diffusion filter, I recommend you take two shots quickly. One with the filter off, one with the filter on. You can then place the diffused shot over the normal shot. Set the diffused shot to Lighten and mask in (or out) the areas where you want the diffusion to show through.

If you’re wondering whether there is a way to get the diffusion effect on a Mac or without purchasing Star Spikes Pro, there is, but it requires a lot of Photoshop twiddling and it is not anywhere near as pleasant as using ProDigital Software’s Star Spikes Pro.

Disclaimer and Book

I am not affiliated with ProDigital Sofware. I am a happy customer of Star Spikes Pro (and another product called Astronomy Tools). I was not paid, or encouraged to write about the product. I chose to because it is that good. Rogelio Bernal Andreo  author of Hasta La Vista Green and purveyor of DeepSkyColors is a friend and a multi-multi award-winning astrophotographer. He has a Kickstarter Project that I recommend you look into called Notes From the Stars

Notes from The Stars: 10 Award Winning Authors