Posted by: kerryl29 | August 29, 2013

Local Contrast Enhancement

In this entry, rather than my usual blather, I’m going to pass along something that may actually be of practical use (sound the French horns!).  Contrast–more often than not, it’s something we want to enhance in a photograph.  Oh, there are exceptions of course, such as the softness present in a foggy scene like the one below.  But even soft scenes like this often need at least a bit of a contrast bump, unless of course you’re shooting JPEGs and have your camera set to enhance contrast on its own.  In the end, though, either you’re enhancing contrast or your camera’s doing it.  Either way, the contrast is being ramped up.

Council Lake in Morning Fog, Hiawatha National Forest, Michigan

Council Lake in Morning Fog, Hiawatha National Forest, Michigan

There’s nothing new about any of this.  So, where’s the tip, you’re asking?  I’m coming to that.  It’s actually a very simple point, but one that seems lost on many folks with relatively little experience with post-processing.

Consider the image below, which has been untouched to this point in Photoshop.

Hiawatha_0038-0042_Council_Lake_de-tc_unedited

In it’s own way, this is a less extreme version of the kind of image that I’ve blogged about before:  lots and lots of dynamic range, with the need to underexpose the scene as a whole to hold detail in the brightest highlights.  Here’s the luminosity histogram for the above frame:

council_full_luminosity

As you can see, it’s left-shifted, but not to the degree seen in the image in the above linked entry.  Extreme measures aren’t needed to salvage the exposure, but the scene definitely needs a boost of some kind. On a global scale, there’s almost no room for contrast enhancement without blocking up shadows or blowing highlights.  And, in any event, a global contrast enhancement is simply going to accentuate the extremes; it’s going to make the darks relatively darker and the brights relatively brighter and that’s not necessarily a solution to what ails the above image.

There are a number of ways to approach the post-processing task in front of us, and here’s one of them:  create a selection that will allow a selective adjustment of contrast in the different parts of the scene that are begging for separate treatment:

  1. the sky and its reflection
  2. the trees and their reflection

Creating the selection via use of the Magic Wand tool was a snap.  The sky (and reflection) are entirely different in terms of luminosity and color than the trees (and reflection), so it was a very simple matter to get a working selection in hand and saved.  Checking an untouched curves histogram of the two separate selections shows just how qualitatively different the two sections are.

First, here’s the curves histogram for the full image.  It’s basically just a different display of the above histogram:

council_full_curves

Now, take a look at the unedited curves histogram for just the sky and its reflection:

council_sky_curves

Take a look at how much room there is to play with, particularly on the dark end of the continuum.

Now, here’s the histogram for the just the trees and their reflection:

council_trees_curves

And here we have tons of headroom for the trees–plenty of opportunity to easily brighten them without concerns about messing with the highlights.

So now we can go about simple sectional contrast adjustments to the two parts of the image.  We can darken the sky (and reflection) a bit via a simple curves adjustment, and add a bit of feathering to the adjustment layer mask.  Then, the trees (and reflection) can be brightened  a bit, also using a basic curves adjustment with an accompanying mask feathering.  (In this instance, I found that a feathering of roughly 20 pixels to each mask did the trick without creating any issues.)

Voila.  We’re done.  Here’s the final product:

Council Lake at Dawn, Hiawatha National Forest, Michigan

Council Lake at Dawn, Hiawatha National Forest, Michigan

I frequently use this very basic Photoshop technique when I’m working on images that have multiple sections each with substantially different luminosity requirements.  The better defined the different sections are, the easier it is to quickly make the necessary selections and apply this approach.  The “patchier” the different sections are (think of many areas of sky “peeking” through the trees above), the more difficult it is, but it’s almost always doable, one way or the other.  Obviously not all images need a technique like this applied to them, but for those that fit the mold, this is a very useful approach with which to be familiar.

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Responses

  1. Reblogged this on This Got My Attention and commented:
    Good tips!

    • Thanks.

      • Anytime. Thank you for providing the information.

  2. Wow! You’re going to cause me to rethink my never edit any photo ways of doing things.

    • Here’s one way to think about it–someone or something is always editing your images. If you’re not doing it your camera is if you shoot JPEGs (depends on the processing settings). And if you shoot RAW, your RAW converter is doing it (based on those default settings). Some form of editing is always going on; as I see it, it might as well be me. 🙂

  3. Great information as always, Kerry. You really know your stuff when it comes to PS post-processing (I remember the education you gave me on my Grand Teton image a couple years back).

    The phrase “local” contrast grabbed me. I might not have given any thought to that terminology, had I not read Jeff Schewe’s book, “The Digital Negative.” In it, he explains that the Clarity and Vibrance sliders on Adobe Camera Raw and Lightroom’s raw processing tools work just on local contrast – particularly in the midtones. I shoot only raw (as I think you do, too). I have found that some careful attention to those 2 sliders in ACR does wonders for most of my images before the even get into PS). I know its slightly different from your topic here – and an image may still need the kind of attention you explain, I thought it was worth mentioning 🙂

    • Thanks, Andy. Yeah, the term “local contrast enhancement” is, as I see it, a concept, not a reference to a specific approach or technique. In its most general sense, it means enhancing contrast at some level below that of a global adjustment.

      I don’t use ACR for RAW conversion (I use Capture NX2), but there are a number of ways to more or less mimic the clarity and vibrance approach with ACR in PS proper. Among those myriad means, the use of a curves adjustment with luminosity masking is one, and I do use that approach occasionally, though not as much as I used to. You can also use one of the Nik plug-ins that I’m sure you’re familiar with–Viveza–for very tightly defined local contrast enhancement. I used that to good effect with a high key image of Double Arch in the Red River Gorge (Kentucky) that I recently licensed to Backpacker magazine for use with a spread they’re doing.

      So, in sum, there are a lot of different approaches that can accomplish, at least conceptually, the same basic thing. Which one to use has a lot to do with the specific effect you’re trying to achieve, your preferred workflow and the tools at your disposal. Thanks for taking the time to add another tool to the box.

  4. Nice Kerry. You threw me a curve with your description of Local Contrast Enhancement (LCE). I learned a different technique for LCE from The Luminous Landscape:

    http://www.luminous-landscape.com/tutorials/contrast-enhancement.shtml

    LCE is usually the first thing I do when editing an image.

    I don’t use PhotoShop. I’ve been a Picture Window Pro user for over ten years now. PWP was 100% 16 bit way before Photoshop. PWP is far less resource hungry, costs less than $100 and is perfect for me.

    PWP added 2 zone and 3 zone enhancements a few years ago. Works very well and PWP creates the masks so you don’t have to.

    Amazing what you can do when you understand curves.

    • Hi, John. Good to hear from you.

      As I mentioned in an earlier comment, LCE really refers to a concept, not a specific technique. As I define the term, it applies to any type of contrast enhancement below the global (i.e. the entire frame) level. That definitely applies to the concept you linked, which has been around for some time. I don’t use that particular approach myself these days, but it certainly can work well.

      Does PWP use a layered approach to image editing? I’ve never been able to tell with any of the brief tutorials on the subject I’ve read. I ask because I do a lot of multi-frame composite work and I can’t tell if that’s viable with PWP or not. If not, it’s a total non-starter for me–but I’m glad to hear that it’s working well for you. It does seem like a more photography-centric program than Photoshop (which is, without question, the least intuitive piece of software I’ve ever used…but I’ve been working with it for a dozen years now, so I’ve become quite used to its quirks and have figured out how to tame it for my needs).

      • PWP doesn’t use layers the way PS does, but there are some powerful transformations within the program that do. PWP has the Stack Images transformation, a powerful tool for combining images. It’s used mostly for HDR but has other uses as well. I’m still on Version 5.0 because I don’t need the newer features. The latest version is 7.0. PWP is the brainchild of Jonathan Sachs, the author of Lotus and an amateur photographer. It’s a terrific program.

        I’ve used layers from time to time but in the Gimp. PWP creates a new image each time you do something. It’s a bit like a traditional wet darkroom in that respect.

  5. Thanks Kerry… i love where you took that lake shot from. I am still entranced by your first foggy shot… my fav. Great info and personal take on the subject… I continue to share your vision with my camera club peeps. I think it is very important to see another’s view and processing on subjects they might take for granted.

    • Thanks very much, Mike. I’ve spent more time shooting in the Upper Peninsula of Michigan than any other single location that’s not within an hour or two of Chicago or Indianapolis. I’ll be heading back up there at the beginning of October, for the first time in five years.

  6. I’m starting to dabble in lightroom. I’m finding it really hard to find that balance between a great edit vs too much processing. As if photography wasn’t hard enough, this post editing is even harder.

    • There’s a post-processing learning curve (believe me, it’s a lot shorter these days than it was 10-15 years ago when there were far fewer tools and even less in the way of accessible instruction, but it’s certainly still there). I’m sure you’ll find that the curve will become less steep with each foray into the world of editing. Keep at it!

  7. Love the foggy scene! Other is great too but that one stands out. Perfect composition and love the few logs to break up the flow

    • Thanks very much, Matt.

  8. Amazing and Thank you so much for sharing

    • My pleasure and thank you.


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