Digital Focus: Punch Up Contrast, Make Slides

These little-known image editing tricks can make marginal photos great.

Dave Johnson

Image Editing With the Histogram

Who's afraid of the histogram? Everyone, apparently.

This slick image-editing feature looks like the kind of graph that no one understood in high school math class, so everyone seems to neglect the histogram. Sure, they'll crop. They'll use gamma. They'll rotate. But tweak the histogram? No way.

A histogram, though, is just a bar graph that shows the distribution of light throughout your picture. Lots of high bars on the right side of the histogram means many of the pixels are very bright; high bars on the left side of the chart means many pixels are quite dark.

So it's unfortunate that few people use this feature. Once you learn the basics, you can use the histogram to put some life into many of your flat, lifeless pictures. Here's my promise: You won't have to do any math, interpret anything, or ever use the expression "x-axis." Let's go.

Interpreting the Histogram

Oops, I lied about not having to interpret anything. Before we can use the histogram to correct our pictures, it helps to know what it's trying to tell us, so let's see how to interpret this graph. Go ahead and open the histogram in your favorite image editor. If you're in Paint Shop Pro, you'll find it in the menu by selecting Colors, Histogram Function, Histogram Adjustment. If you have Adobe Photoshop, it's located under Image, Adjust, Levels.

The histogram curve is little more than a graph that shows you the amount of color information stored in a picture, or, in plain English, it shows how dark or light your picture is. The x-axis (lied again...sorry) represents the tonal range of your picture, from pure black to pure white. The y-axis shows how many pixels are bright, dark, or somewhere in between.

A properly exposed picture is represented by a grouping of bars that span the entire tonal range from white to black. The shape of the graph itself depends upon the kind of picture you've taken, though it often looks like a traditional bell curve (fat in the middle and tapering at the ends). Check out a typical histogram.

But suppose you have a picture in which the bars of your graph trail off to zero before reaching the right edge of the graph. That "gap" means that the lightest-colored pixels in your image aren't pure white, and the picture might benefit by increasing the highlights.

Now look at this unhealthy histogram: Here the gap on the left that indicates the picture's shadows aren't pure black, and we might want to fix that.

Equalizing the Histogram

Now that you know what the histogram is telling you, fixing it is a snap. Under the graph you should see three slider controls. If your picture is missing highlights, drag the right-most slider to the left until it meets the histogram curve. You've just told your image editor to recalibrate the picture to make the highlights brighter, increasing contrast in the picture. You can do the same at the low end; drag the left-most slider to the right to close any gap in the graph. That recalibrates the darkest pixels so the shadows and darkest regions use the full tonal range available.

If the picture looks better but still needs more work, try the middle slider. That controls the gamma level of the picture, which is akin to the picture's brightness level. You can move the gamma slider to the left or right to adjust the overall brightness level of the picture.

But I did keep one promise: We didn't do any math.

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Mini Review: HyperSnap-DX

The layout of the typical PC keyboard hasn't changed in so long that it still has a button labeled Print Screen (or, on more terse keyboards, PRT SCR). In 1983, that button actually meant something; you could send any DOS display to the printer.

Today, though, getting on-screen data onto paper or into a graphic file is more complicated. While the Print Screen button can grab a Windows display and put it in the clipboard, lots of other applications don't work that way. If you want to capture a screen from a game, many graphics programs, or most video editing programs, the good old Print Screen key won't work. That's why you should have HyperSnap-DX in your graphics toolbox. HyperSnap can capture any kind of display and save it in a standard graphic file for printing, adding to a PowerPoint file, or pasting into some other document.

Though HyperSnap costs $25 to register, it's well worth the fee to be able to grab and paste images from any video or graphics display on the PC. I've successfully captured hard-to-get images such as video from Direct X applications and DVD players. Download the trial version (which puts its logo on every screen you capture until it's registered).

Q&A: Making Slides From Digital Images

Is there such a thing as a slide printer? I want to get some slides made from pictures I've taken with my Nikon Coolpix 990.

-- Eleanor Lundquist, Centralia, Washington

Well, I have some good news and some bad news. First, there's no practical way to make your own transparencies from digital images. There are simply no printers that make quality 35mm slides. The alternative would be to photograph your digital image using a 35mm camera and slide film, and that would be neither easy nor of sufficient quality to bother trying.

But there's another way. Most custom photo developers can generate 35mm slides from digital images at a reasonable price. You should start with the highest resolution you can get your hands on--the 3.3-megapixel image generated by most quality digital cameras will give you a good-looking slide with no visible pixels or jagged edges. Ask your local photo shop what format they require. You may need to save the image as a TIF and copy it to a CD-R disc, for instance.

Send your questions to question@bydavejohnson.com, and please be sure to let us know where you're from.

Hot Pic of the Week

Get published, get famous! Each week, we select our favorite reader-submitted photo based on creativity, originality, and technique. Every month, the best of the weekly winners gets a prize valued at between $10 and $100.

Here's how to enter:

Send us your photograph in JPG format, at a resolution no larger than 640 by 480 pixels, to hotpic@pcworld.com. Larger entries will be immediately disqualified. If necessary, use an image editing program to reduce the file size of your image before e-mailing it to us. Include the title of your photo, along with a short description of the photo and how you photographed it. Don't forget to send your name, e-mail address, and postal address. Before entering please read the full description of the contest rules and regs.

This Week's Hot Pic:

Missed by Pat Harrington, Vallejo, California

Pat says: "I took this picture at a San Francisco Giants game in the early afternoon. I used a neutral density filter on my Sony DSC70, but all the settings were automatic. To add a little depth to the picture, I loaded it into Photoshop Elements and copied the image into layers. A added a 2 percent Gaussian blur to what would become the background layer, and then used the eraser function to erase the blurred image of the child--thus creating better depth of field and making the child stand out. I caught the missed swing at just the right time--and loved the look of concentration on his face!"