Category Archives: Color Correction

We Are Always Tweaking

Original Publish Date: 12-November-2015
Last Revision: 12-November-2015

When we get questions on our older columns, we often answer them directly and update the articles to reflect new information. For example, when we originally published our three part series on Finding and Photographing the Milky Way we had no clue they would be our most read articles. Over time we added more charts, and tables, including a table listing when the best time is to spot the Milky Way – alas, not October through February.

The Milky Way Series

Pointy Land
The articles in the Milky Way series are:


Meteors and Meteor Showers

Celestial Slasher [C_224-9234]

We have also made periodic updates to our articles on photographing meteors and meteor showers.  We point this out because the best shower of the year is the Geminids and that shower occurs December 12-14.  Start planning right now!

To help you out, we have begun adding “Original Publish Dates” and “Last Revised” dates to our articles.  Of course most of the principles we have written about are timeless.

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!

Extraordinary Vision

Last month, one of Steven’s images was featured in the great (and free) Extraordinary Vision magazine issue 9 which is published online via iTunes.  

I_305-0347This month in Extraordinary Vision issue #10 you’ll find 17 pages of instructions on finding and photographing the Milky Way. If the article seems familiar, it is! The Extraordinary Vision article is an updated and combined version of our three-post series on the Milky Way:

If you haven’t checked out the magazine, please do – not just because of the Milky Way content, but because Angelo Ioanides does a fantastic job curating and writing great content. And it’s FREE – just like the content on our BLOG.

First page of the article.

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Click the image below to find the Extraordinary Vision Magazine:

Extraordinay Vision Magazine published on iTunes

 

 

 

 

Filters and the Night Sky

I wanted to buy a light pollution filter. I saw there are 2 kinds of filters UHC (Narrow band filter) and the Broadband Filters (e.g. CLS). Which one should I get?

I think the easy way to answer the question is as follows.

For Narrowband substitute the word Red and for Broadband substitute the word Polarizer.

A Red filter will definitely block out light that is not red. A polarizer lets all colors through roughly equally, but a polarizer does diminish the total amount of light. If you use the red filter you’ll still see, but you’ll see only the red component of the light. If you use a polarizer things will look normal, but dimmer.

The same is generally true for Narrow and broadband filters. Of course a Narrowband filter doesn’t have to be red, it could be green, blue, ultraviolet, etc and a broadband filter also doesn’t have to be neutral. Indeed, the idea behind a broadband filter is to pass as much light as possible in as many wavelengths as possible EXCEPT for the predominant wavelengths of the light pollution.

The only broadband filter I’ve used, the Astronmik CLS, is a light blue color and definitely gives things a blue tint that requires correction.  The filter I have drops into my camera just ahead of the sensor. That setup makes is more versatile, but it only works on Canon cropped cameras, not on my 5D II, for example. I purchased my filter from OPT for about $130 and frankly haven’t used it much because it got stuck in my Canon 40D.

One problem with light pollution is that it comes in many different wavelengths (colors) depending on the light source: tungsten, fluorescent, halogen, low or high pressure sodium vapor, etc. So the effectiveness of any broadband filter changes significantly with the lighting conditions around your photography/observing location.

On a more practical matter visual astronomy is usually done with a telescope or binoculars and the filter must match (one of) the standard eyepiece sizes or simply be hand-held. Visual observing is also different from photography in that color is easily recorded by a camera, but the dim light of stars, galaxies and nebula is almost always perceived in grayscale by we human observers. For photography the filter size depends on where the filter is placed in the optical system – thus you may need differently sized filters for different uses. I’m much more of an astrophotographer than an astronomer so I can’t really comment on what works best for visual astronomers.  Fortunately Shawn Grant does a great job explaining this in his article.

One filter that MIGHT have some significant application in landscape astrophotography is a graduated neutral density filter.  But I’m not really a big fan of these filters as I describe in a previous article.