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This tip article by Brian Dilg comes to us courtesy of New York Film Academy Photography School, where he serves as the Chair of the New York Film Academy Photography Conservatory. Dilg is an internationally published and collected photographer and award-winning filmmaker with over 20 years of professional teaching experience around the world.
While the term "contrast" is familiar to anyone who has adjusted their television, it's also commonly misunderstood in terms of how it affects photographs. If you turn up a "contrast" control on your camera or in your image-editing software, what you're doing is pushing all your midtones towards black or white. If you begin with a very flat image that's all midtones, this can be an effective way to expand the tonal range of the image and produce a better-defined image. (Compare the unadjusted and enhanced-contrast and clarity versions of the image.)
Pushed far enough, you would eventually end up only with black or white, and no midtones at all. A U-shaped histogram would result. (See the "extreme" contrast version)
Where contrast is often misapplied is when photographers want to bring out detail in areas that are muddy because they consist of very similar tones. Adding contrast seems to make sense – a contrast in tone or color is literally what makes one pixel distinguishable from another - but the problem is that global contrast control is just that – global. It looks at the tonal range of an entire image, and pushes everything towards black or white. Setting the overall tonal range of the image is a basic and necessary early step in your post-processing, but that is just the beginning.
To bring out detail, what you want to do is to exaggerate the subtle differences between pixels within each tonal framework. You may also want to adjust contrast - the overall tonal range - within each framework, but that is not going to be as effective in terms of bringing out detail.
Within Adobe Lightroom or Photoshop's RAW processor module, the Clarity slider does just this; in Apple's Aperture, it's called Definition. Both describe themselves fairly accurately as "local contrast controls." (Although this can be done in Photoshop through several steps, I advise doing as much as possible while you are still working with the original RAW file.)
Compare the unadjusted whiteout image to the one with enhanced contrast and clarity. Every detail is more clear, and the image contains deeper blacks and brighter whites. The low-contrast version is at the other extreme – very flat and murky. Most of you would probably agree that the version with an increased contrast and clarity is the better image – it "pops."
However, what I did in the final version of the image is to apply clarity, contrast, and sharpness selectively to enhance the atmospheric effect created by the blizzard, and render the image more three-dimensional. I used local adjustments (adjustment brushes in Lightroom) to increase all three under the bridge and on the tree and lamp post, but I lowered all three on the background elements to make them appear to recede. This is simply enhancing the atmospheric effect: the farther away something is, the more particulate is in the air between the camera and the subject, making objects less sharp, less saturated, and raising the black point.
I also applied selective local contrast and sharpness to the B&W landscape of the Isle of Skye, Scotland. When compared to the untouched original image, this may seem extreme, but remember that the viewer will never be shown anything except the final image.
Ultimately, how you orchestrate tone and color is what determines your personal style.