Tag Archives: exposure

Why Aim North?

The Advantages of Shooting To the North

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!).
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]
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]
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.
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.
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]
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].
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.
If I know my latitude I know how high to point the camera and be guaranteed to get a circle in the view.
I do not need to know what constellations will be visible in the direction I will shoot.
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

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

Eastern View

Western View

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.

The 5 Most Used Photo Enhancement Techniques – Part 2

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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.

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

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

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

Here is what Auto did for this image:

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

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

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

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.

Before Twiddle Hand curve adjustment

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).

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 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

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.

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

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

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.

The White Balance tool in Adobe Lightroom

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!

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.

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!

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.

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!

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

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

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, 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

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!

Creating a Night Panorama

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That’s it. You just found the perfect composition but there is a problem. The interesting bit does not fit with the other interesting bits. So you sacrifice and change to a wider angle lens but that does not improve the shot. In fact, you can’t get an image wide enough or tall enough. Let’s change our frame of reference for a moment because not many people think about the ability of panoramas to connect the foreground to the heavens.

Although taking truly panoramic star circles is next to impossible within a reasonable budget, you can connect the earth with the sky with a little bit of planning and some tricks to aid in your alignment later in the process.

We are proposing a vertorama that is a “vertical panorama” to extend our photo to the ground and blend it into the star trail on top. Our approach will be to shoot in landscape mode and tilt our camera up as we progress. We can take a series of two or three shots but it will look odd if the star trails don’t extend into the edges of solid land (lower portions). We also have to make sure that we don’t end the last frame too high as this leaves the star trail disconnected from the ground (lower) images.

Gear

The minimum amount of gear required is a camera a tripod and an interval timer. However the whole process is going to get much easier if we have a method to align the “no parallax point” with the axis of rotation. Huh? What did you just say…If you didn’t get that last sentence I suggest you read our primer articles on panoramas here and here or by following links out to other resources.

Planning a Shot

By this time I am assuming that you have read all of the prior articles on shot planning and alignment. If not they can be found here, here, and here. Now that we are up to date on planning and alignment we can get into the gory details. We are going to have to take some additional steps to help in the alignment in post processing.

I can get obsessive about the details but I want to do it right not get back to my computer to discover I spent 4 hours in the cold, dark night with stars and nothing interesting in the foreground. I begin with an idea of how I want the image to look then I walk around with a compass and the local north declination adjustment to fine tune where the center of rotation will be in my final image. I set up my tripod where my chosen foreground will be in alignment with Polaris (aka The North Star). Before I take the first photo I know where Polaris is going to appear in my frame. When I am really particular I will use a laser line to insure I have the object exactly where I want it in the photo. I then level the tripod and assemble the pano head. I use the pano head to determine the elevation of the north star this helps me know exactly how high the star with be in the sky. This helps me to see where the star circle is going to be in the photo. [Editor’s comment: If you know the angle of view of your lens you can determine the altitude of the north star by using your camera’s field of view as a measurement]. Knowing how high Polaris is in the sky will help me to determine the overlap I need to include all of the elements in the photo I want. This all may seem like over-kill but to go home and thinking you have an image of a lifetime only to find you have a dud is not fun.

Shooting (and Bracketing)

I take a lot of photos with different settings until the blue period ends and the stars begin to appear. I make sure that I take a lot of bracketed shots that have 30% to 50% of overlap. Having plenty for foreground images to choose from later is going to be very helpful when merging the final images. Once I am satisfied I have enough images the next step is to lock the camera and tripod down tight to take the series of star trail photos. If I didn’t get to my intended location in time and still want to get foreground shots it is still possible. Darkness merely means that my foreground exposures are going to have to be long, perhaps very long. Alternatively I can light the foreground with a flash light, strobe, or fire or I will let you borrow some light from my moon. 🙂

These are some of the images the top and bottom of the vertorama. I took right before the blue period ended. You can see the various bracketing and over lapping I did.

Post Process

I assume that you already know how to process your star shots into star trails. If you need a refresher check out Steven’s articles on star trail creation. I like to do a few different versions of the with stars because I like to include different amounts of blue and so I have an easier time blending them in later in the stitching process.

Just some of the Star Circles I generated using different amounts of blue period photos.Combining a star circle with a foreground can be done with several different stitching engines, I prefer PTgui, however for other stitching engines the workflow is similar. Your images may be bright enough to do the whole process with Photoshop’s stitching or in Microsoft ICE engine but if you are blending in photos to get a darker sky then Photoshop might be a dud. Also these stitching programs will not allow you to add control points to help align and warp the image to the background and let me be the first to say the alignment and warping the foreground image is not fun or easy.

Import your Images

I like to import a lot of different bracketed images into the stitching engine just so I can have some variety to work with. Also it will allow me the automatically find control points on overlapping images and then tell the software that the other images have zero pixel shift from that image in the bracket series. This allows me to save time by putting control points on only the images that are dark or match the star circle image. Thus I can align and blend the pano in one step then use Photoshop to blend in the stars.

Once imported click the align images, did it work…if so hooray!! You now only have a small amount of clean up to do (skip down to the projection part of the article). If not then you have to add some control points and align the images yourself. Control points are areas on an image that match in overlapping images the software needs to know these areas to know how to warp adjacent images to stitch them together. So lets look at how PTgui does this. Below is a screen shot of PTgui’s control point placement feature.

Control points selected between the star circle image and the bright forground image. I pick areas in the image that have 1) sharp contrast, 2) Jagged edges and 3) don’t move.

All you have to do is open the adjacent images at the seam and then zoom in to find distinct points that match. I like to use object with good contrast and unique shapes to help guide my cursor to a pixel accurate match.

In the image above you can see that the transition between the rock and the sky is the area of overlap. I follow the rock edge because of the contrast between the sky and the rock but also it has bumps that are easily distinguishable between the top and the bottom photos. Once I have these set I do the same for the star trail photo see below.

Aligning the Star trail image with the photos from the blue period

I will align the star circle photo with the corresponding photo of my foreground just so I have less stitching errors and it is easier to align. Again if the star circle is light enough then these images may automatically align.

Projection and orientation

Once all of the images have control points then I will go and see how the preview of the image looks in the panorama editor.

Looking at the stiched images in the panorama editor for the first time to see the errors in overlap and the corrections needed to correct the distortion.

You can see the top and bottom images of the vertorama are properly aligned at this point don’t worry about the blending we will handle that later in photoshop. Two things are very off, causing distortion of the star circle 1) the projection and the vertical height of the image. The projection is the way the images are projected on to the inside of a sphere during the alignment. If you are interested in the types of projections (and there are many in the image below) and how the distortion affects the overlap and warping of your image more info can be found here. I am not interested in the type or how it works in this case I am just worried about what looks right. For most vertorama star circle images the “Rectilinear” projection often looks the best but is not always the case.

Correcting the projetion to make the photo appear flat and not as distorted at the edges.

We can quickly correct the oblong star circle by moving the top image toward the bottom. This will change the amount of space that is blank but once we crop the image those areas will not longer be visible anyway.

Changed to rectilinear and moved the whole image down. You can see I changed the vertical FOV with the slider on the right (right red arrow) I changed the projection at the top to rectilinear. and the line in the middle shows the movement of the image down.

Outputting the files

Once you are satisfied with the preview the next step is to use the image optimizer to hone the control points to reduce the error. It is so easy I am not even going to include a photo just click and tab and click optimize. It will give you a rating “very good”, “good”, “not bad”, etc. then suggest some corrections my usual experience is just accept them they more often help then harm.

The only step left is the output the files and then mask them in photoshop. Go to the “Create Panorama” tab and preview the settings. You can see the settings I use is to output the images as a “.psb” for use in photoshop but you can output what ever you would like. The most important is to output into 16bit layers under the “LDR file format” or “HDR file format” settings. This is shown in the screen shot below. Since the blending is going to cancel out some of the stars the aligned images need to be output in seperate files so. I will uncheck the image that represents the aligned star circle in the screen shot below this is “Image 6” the rest of the images are the aligned HDR brackets. Then I will name the file something like “file….SC_BKGD” were file is the former file name and the “SC_BKGD” stands for “Star circle Background”.

Outputing the top and bottom layers

Once this is done stitching I output the star circle image alone. So in this example I would un-check the boxes next to images 0-5 and only output image 6. So once all of these images are outputted I select them and open them as layers in photo shop. If your blending went well in PTgui then great skip the next step and forward on to the next. If the blending shows seams or other artifacts of stitching follow then next steps.

If the blending was bad then go back to PTgui mask out the areas the blending did not work so well if you have PTgui version 9, if not then output all of the layers and we will mask and clone in photoshop. I picked this example specially because I had blending issues in the past so if you have blending issues you will know how to approach them.

This is my stitched Foreground and star circle images notice the two red arrows are places where the blending did not work so well

The first thing to try since the layers are aligned is the auto blend layers under the Edit menu. Select the top and the bottom then navigate up to “Edit” and click under “auto blend layers”

This is the first tool I reach for when blending is the auto blend layers. Once the layers are aligned (and HDR-processed) thanks to PTgui the blending in Photoshop is usually easy.

If the auto blend function does not work it is time for some good old fashion hand blending. I will open the individual blend layers and the PTgui blended photo with blending issues. I will use the photo with blending issues as the background and layer over the top the individual planes to blend by using a mask to gradually make the layers more transparent using a big soft brush. I slowly make the seam fade or use the surrounding colors to add detail. I will also use the clone stamp to replicate areas like clouds and blend them into each other. This takes a lot of patience and practice to make some areas look “normal” but keep zooming in and out to see what affect you are having on the whole photo and local areas.

Adding the Star Circle

Once the blending the top and bottom image is finished the star circle can be added. Since you exported it as a separate layer out of PTgui this can be brought into photoshop as a layer in the document. Opening the photo as a layer then by changing its blend mode to lighten or screen blend mode then bright stars will out shine the dark background. Thus adding the star circle to the finished photo was easy. Don’t forget to mask out some of the areas were affected by the screen blend. Say in cases of light pollution the foreground might be brighter then they should be. Crop then your done.

This is the final image after the stars are added as a background layer and blended in using the screen blend mode.

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