One of the factors that can often make the difference between a photo being eye-popping mind candy and lackluster visual soup is the appropriate amount of contrast. Photographically speaking, contrast is the difference between the light and dark areas of an image. The less difference, the less contrast and the more difference the more contrast, one of the few things in the confusing world of photography that has a direct and logical correlation. In some images, such as foggy landscapes, low contrast is the goal. For other images, low contrast makes the image look muddy, washed out and lifeless. Depending on the nature and direction of the light source and how the light is interacting with the atmosphere, digital camera sensors naturally capture some images with less contrast and others with more contrast. Images that come out of the camera with more contrast are not usually a problem since our eyes and brains see it that way automatically. However, digital images often have too little contrast as captured by the camera. Fortunately, digital imaging software such as Photoshop gives us tools to bring low contrast images back from hazy obscurity. Below I will outline a few simple techniques to put some pop back into your low contrast images.
Open a low contrast image in the photo editing software of your choice. I use Adobe Photoshop, so my tips will be specific to that software, but most programs use very similar approaches.
Check the levels. In Photoshop, go to Image>Adjustments>Levels (or type control + L) to open the Levels dialog box. The histogram shows you the spread of color values in your image. The highlights are on the right and the shadows are on the left. If either end of the histogram doesn’t reach the end of the graph then your lights, darks or both aren’t as light or dark as they could/should be. By pulling the sliders in to meet the ends of the histogram data you will be darkening the darks and lightening the lights, which by definition will increase the contrast of your image. Hint: pulling the sliders past the end of the histogram data is generally a no-no. It will “clip” information from your image causing some areas to be completely black or completely white. Avoid this unless you are purposefully going for a Euro-fashion, impressionistic look.
Create an “S” curve. Making Levels adjustments, as explained above, is usually a good place to begin on every image. However many images will have Levels that are already in the right range. Some images with the Levels in the correct range will still benefit from some additional contrast control. Open the Curves dialog box by going to Image>Adjustments>Curves (or type control + M). (Note: Photoshop Elements does not feature a Curves adjustment so you are stuck using just Levels.) The Curves dialog features a grid with a 45-degree diagonal line bisecting it. The lower left of the grid represents darks and the upper right represents lights. It is most often desirable to try to increase contrast without losing detail in the shadows and highlights, as discussed above. To increase shadows without losing detail, click on the diagonal line towards the lower left and drag that point down slightly. To increase the highlights without losing detail, click on the diagonal line towards the upper right and drag that point up slightly. This will create an “S” curve on the graph. Such an “S” curve increases contrast in your image. It is easy to go to far with this adjustment, so watch that itchy mouse-button finger. If you do go too far it is a simple matter to re-click each point and move it up or down until the right amount of contrast is achieved.
Add USMcontrast. Sometimes I want the edges between dark and light areas to really pop, and for this I adjust contrast using the Unsharp Mask filter (USM). To open the USM dialog box go to Filters>Sharpen>Unsharp Mask. Unsharp Mask is most often used (even though it doesn’t sound like it) to add edge sharpening (which is really just a matter of increasing contrast along fine edges) to an image before printing. However, by really tweaking the controls we can also use it to increase contrast. Leave the threshold set to zero, but increase the radius to 95 and set the amount somewhere between 8 and 15 depending on the amount of contrast you want. If you increase the amount beyond 15 or 20 you will begin to see halos form around the edges of objects, a sign of too much edge contrast.
Act locally. Sometimes only certain areas of an image will need more contrast. Use the Lasso tool to select a specific area and then apply any of the above techniques to just that area.
Don’t over do it. An image with the right amount of contrast is crisp, sharp and vibrant. It really pops off the page/screen. An image with too much contrast looks cartoonish, has a loss of detail in the highlight and shadow areas and is immediately identified by the eye as false. There is a fine line between just right and too much. As with any digital adjustment, it is easy to get greedy. Exercise self-control and good taste.
Don’t be destructive. Many image-editing programs (Photoshop included) have a specific contrast adjustment feature and also a variety of “Auto” adjustments targeted at contrast among other things. These features offer you very little control over the results and often make very bad adjustments, including the senseless destruction of data in your shadows and highlights. These features can be handy for quickly processing the 300 photos you took at your dog’s birthday party, but I don’t recommend using them on any image you want to have the highest level of quality and detail.