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One of the qualities of an image that tends to define good quality is contrast. It most certainly isn’t the only factor that determines overall quality, but it is an important one. Higher contrast is generally greeted with more enthusiasm and appreciation.

Contrast is generally defined as the difference between the darkest and brightest pixels within an image. When you have low contrast, there is minimal difference between those pixels. This translates into reduced tonal range within the image, and an overall muddy appearance. Optimizing contrast extends the tonal range, adding “snap” to the image, while also improving the perceived focus. Put simply, most images will look better when you properly boost contrast.

Let’s take a look at the methods available to optimize contrast in Photoshop (including Elements). For photographers just getting started with digital imaging, the most basic tool for adjusting tonality of an image may be tempting. This tool is the Brightness/Contrast control, but I don’t recommend using it. The short explanation of why I don’t recommend using the Brightness/Contrast control is that it doesn’t offer enough control.

The more detailed reason why Brightness/Contrast is best avoided is that it doesn’t offer enough flexibility when adjusting contrast. The Contrast slider affects both black and white points at the same time, and to the same degree. In other words, you’re giving up just as much detail in the highlights of your image as you are in the shadows.

The Levels control, on the other hand, allows you to adjust the shadows and highlights individually. This is important, because if you need to give up detail in an image in order to improve contrast, it is best to sacrifice detail in the shadows rather than highlights. When viewing an image, we accept the fact that shadow areas are dark and we might not be able to see detail in them. When detail is lost in the highlight areas, the image simply looks “wrong”.

A good general rule when making adjustments in Levels is to bring the black and white point sliders in to the edge of data on the histogram (where the “mountain” first starts to rise at either end of the histogram data). This will effectively make the darkest pixels in the image black and the brightest pixels white. This maximizes tonal range within the image, and improves contrast. However, sometimes you want to add a bit more contrast to an image. In those situations, it is best to bring the black point in just a bit more, leaving the white point alone.

For even greater control over the adjustment of black and white points in Levels, you can use the clipping preview display. To do so, hold the Alt key (Option key on Macintosh) as you adjust the black or white point in Levels. When you do so, the display will go all black (for the white point adjustment) or all white (for the black point adjustment). As you slide the slider inward, you’ll start to see pixels appear within the image. The color of the pixels tells you which channel is losing detail in those areas. When a pixel appears black (or white), all detail on all channels has been lost, shifting the actual pixels to black (or white). By using this clipping preview display, you can make an informed judgment about how much detail you’re willing to give up to optimize contrast within the image.

Setting the black and white points for your image certainly helps to improve contrast, but you can only take those adjustments so far before causing problems. If your image is still looking a bit muddy after adjusting black and white points in Levels, your next stop needs to be the Curves adjustment.

You’ve probably heard of the “S” curve adjustment, and using such an adjustment can help improve contrast in your image without sacrificing any highlight or shadow detail. Unlike the Levels adjustment, which only allows you to set black point, white point, and middle tone values, Curves allows you to adjust any range of tonal values within the image. The “S” curve improves mid-tone contrast without sacrificing any highlight or shadow detail.

To create an “S” curve adjustment in Curves, click on the curve line about 20% from the white end and 20% from the black end. This will place an anchor point at each of those positions. Drag both of these anchor points inward, moving the upper point slightly to the left and the lower point slightly to the right. You don’t need to move the anchor points very far to improve mid-tone contrast. The result is improved overall contrast without a loss of detail.

All of these methods will help you improve the overall contrast in your image, but they are just a start. As you are optimizing each of your images, work with Levels and Curves to fine-tune the overall contrast without sacrificing excessive detail, and you’ll be on your way to producing the best images possible.

Tim Grey is author of Color Confidence: The Digital Photographer’s Guide to Color Management and co-author of Real World Digital Photography 2nd Edition and Photo Finish: The Digital Photographer’s Guide to Printing, Showing and Selling Images. He publishes the almost-daily Digital Darkroom Questions (DDQ) e-mail in which he answers questions related to digital imaging. Tim also teaches courses at the Lepp Institute of Digital Imaging (www.leppinstitute.com) and makes appearances at other venues. You can visit his website at www.timgrey.com.

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Very clear and precise instructions that can be put into pratice immediately. Posted by: Denis Aug 10, 2007 @ 7:45 PM EST

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