Digital Focus: Punch Up Photos With the Histogram

Feature: Liven Up Your Photos With the Histogram

What does it take to make a good photograph? Before you start talking about composition, the rule of thirds, kittens hanging from tree branches, or sunsets, consider this basic element: proper exposure. A well-exposed image has just the right amount of light in the scene to properly illuminate the subject, so that images are neither too dark or too light. A good picture has a good exposure "spread" over the total range of pixels in the image.

The best tool to use for correcting exposure is the histogram, a graph that shows how many pixels are dark and light in an image.

Interpreting the Histogram

Where can you see a histogram? Well, many digital cameras have a histogram mode; take a picture, and you can immediately see a histogram to assess its quality. In last week's newsletter, in fact, a reader's question referenced a friend who uses the histogram to discard badly exposed pictures without even looking at them.

I wouldn't go that far, but I will validate the notion that a camera's histogram can give you a very good idea of whether a photo will look good on a computer monitor and in print.

The histogram on a camera is really just for reference. Your image editing software probably also has a histogram display--and we can use that one to substantially improve your photos. Take a look at Paint Shop Pro histograms for a couple of run-of-the-mill images: coins and dancers.

The left side of the graph represents the darkest part of the image, while the right side is the lightest. The vertical axis shows how many pixels are in each of the image's brightness levels. A graph like one for the image of coins has a lot of midtones, while the dancing girls image is mostly filled with dark pixels--it's underexposed. We can use that information to tweak the brightness and contrast.

Using a Histogram Adjustment

I use the histogram to adjust many of my pictures, and I suggest you try the same. It takes only a few seconds and can improve almost any shot. Most good image editing programs--like Paint Shop Pro, PhotoShop, and Photoshop Elements--have a handy tool for adjusting the light levels in your image using the histogram chart and a few sliders. In Paint Shop Pro, it's found by choosing Adjust, Brightness and Contrast, Histogram Adjustment. Adobe Photoshop Elements, on the other hand, puts this control in Enhance, Brightness/Contrast, Levels.

Regardless of which program you use, the tool works more or less the same way. Just move the triangle sliders under the histogram to set the white and black points, stretching and optimizing the distribution of brightness information in the image.

Suppose you have an image like one I took at a play. Open the image in Paint Shop Pro and choose Adjust, Brightness and Contrast, Histogram Adjustment. Since the curve of the graph drops off before it reaches the right side, that tells us there are very bright few pixels. To fix this, drag the white triangle under the graph to the left to meet the point where the graph ends. In other words, you want to stretch the graph to take advantage of all the available space. That sets this point in the image as white, and should brighten the image. You should see the graph stretch as you drag the end points. Close the adjustment tool, and you'll see an image that has better exposure.

In your own images, be sure to set both the white and black points in the histogram, if necessary. Finally, use the gamma slider--the gray triangle--to adjust the overall brightness level in the image's midtones. That's all there is to it--and those 30 seconds just gave your photo more punch.

Dave's Favorites: ShortCourses in Digital Photography

Of course, I know that most of my longtime readers already know the basics of digital photography. But my boss tells me that we get readers all the time. (Welcome aboard, folks! Good to see you.) And newbies can sometimes benefit from an overview of the basics of digital photography--like how to shop for a camera, how to change file size, and how to use your camera's various exposure modes. For you old-timers, what about your friends, cousins, and sisters-in-law? Getting tired of explaining the basics of digital photography to them? Steer them to some good resources.

Thankfully, you've got a lot of options. I need to put food on the table, so, I always recommend my own book, How to Do Everything with Your Digital Camera, which is available at Amazon.

And you can always browse through our very own Digital Focus archives to read old features or see previous Hot Pics of the Week.

But if you're looking for a great little collection of tips, tricks, tutorials, and novice-friendly explanations, be sure to visit ShortCourses.com. This site, built by author Denny Curin, represents the fruit of his research while writing his own book on digital photography. Denny has collected a lot of interesting and useful information and arranged it into a bunch of lessons (like "Choosing a Digital Camera" and "Displaying and Sharing Digital Photos") as well as a Web log with various discoveries he has made along the way. Be sure to check it out--or e-mail the link to those friends who keep asking you questions.

Q&A: Can Memory Cards Affect Image Quality?

Has anyone compared various memory cards to see how they affect factors like resolution, color, sharpness, and so on? I have two Kodak digital cameras. One uses CompactFlash, while the other one takes an Secure Digital memory card. Both have about the same resolution (3.2 megapixels). But it seems to me that the camera with the CompactFlash card gives sharper photos. I realize the cameras themselves are different (one is a DX3900, and the other is a DX6340). What is the difference in the quality provided by the two cards?

--Stan K, Barstow, California

Actually, Stan, you answered your own question at the end of the letter. It's the difference in the two cameras--their optics and image processor--that result in differing levels of sharpness. The memory cards are not to blame.

The key here is the word digital. Unlike film cameras, which use an analog media that can affect the quality of the image, digital cameras store their images in digital files. Memory cards (no matter what type they are) store digital files, just like floppy disks, hard drives, and optical discs. A digital photo file will contain exactly the same information no matter which media it's stored on. As a result, the photos that file yields will all be of the same quality--and copies will be identical to the original. Your different memory cards will not affect that basic fact.

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 $15 and $50.

Here's how to enter: Send us your photograph in JPEG format, at a resolution no higher than 640 by 480 pixels. Entries at higher resolutions 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 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 regulations.

This week's Hot Pic: "Sunset," by Claude Adams, Luling, Louisiana

Claude says that he took this picture with a Fuji FinePix 3800 at Lake Catouhatche after a fishing trip in Southeast Louisiana. "The portion of ground that's visible in the middle of the lake contained a fishing camp 20 years ago and has since eroded," he says.

We want your feedback! Send your comments, questions, and suggestions about the newsletter itself to comments@bydavejohnson.com. If you have a question that you'd like to see answered in the weekly Q&A, send it to question@bydavejohnson.com.

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