By Lou Dolinar
Third in a series
Updated Feb. 14, 2006

Every photo retouching program takes a slightly different approach and has a different target audience, from rank amateurs to professionals who shoot for National Geographic.

Still, all descend from a common ancestor, Adobe Photoshop, and incorporate some basic techniques you should know. Here's where to start:

Cleaning. The first step is purely mechanical: Lightly blow off dusty negatives and slides with compressed air or a little squeegee bulb you can buy at a photo supply shop. Invest in some cheap, thin, cotton gloves, like the real photo experts wear, when handling photo material. Scanner glass also attracts fingerprints, so pick up some cleaning supplies for the glass as well. More extreme measures, like brushing and washing, can damage film and should be left to the pros.

Cropping: To a pro, cropping is second nature; to an amateur from the pre-digital age, a mystery. Until quite recently, with even zoom lenses a rarity, what you saw was what you were stuck with. All of which means old photos by amateurs are rarely perfectly composed and benefit from cropping. The basic idea for run-of-the-mill family photos, as we noted last week, is to crop at the time you scan and boost resolution to acquire the same pixel count as you would have used for an uncropped photo. Another school of thought suggests that for historic and archival scans, forget about cropping and max out on resolution.

Think about your output device when you're cropping. Slide shows are invariably horizontal, but for printing, sometimes it makes sense to crop a horizontal shot with dead space on either side into a vertical 8-by-10.

Conversely, you can zoom in on faces in a group shot and turn a vertical picture into a horizontal one. Your scanning software generally will allow you to lock the "aspect ratio" of the output to match the paper size you're using, so you just manipulate a little marquee to select what you want.

Digital cleanup: Most programs have an option to automatically remove dust, dirt and fingerprints. These usually work pretty well, especially with high-end film scanners, but consumer-grade products tend to soften the picture overall, and may obscure details. Whether this matters depends on your prospective use - probably not for digital slide shows and 4-by-6s, but you need all the quality you can get for an 8-by-10 or larger print.

Manual dust removal is one of the fundamental features of serious image-editing programs, sort of like cut-and-paste for word processing. As such, removing dust is a nice baby step for the aspiring photo retoucher.

Details vary among programs but the idea is to zoom in tightly on the area to be retouched, then take a sample (sometimes referred to as cloning) of an adjacent area that resembles the area you want to repair. You then spray, stamp or brush the cloned value into the area you want to correct. The repair can be as simple as covering a dust spec with the correct cast of blue for a sky, but you can also copy patterns and textures to, for example, fill in a portion of a dress that's been destroyed by a tear in a print.

Lighting. While there are many specialized controls, the histogram, aka levels function, rules here; indeed, variants of it are even showing up on consumer-grade digital cameras. This control consists of a graph (the histogram) of the photo that shows the number of pixels, by brightness, from black at one end to white at the other, across 256 shades of gray.

Beneath the graph are three arrows, one for adjusting black level, one for white, one for gray. Most photos don't use the full tonal range available - this shows up as blank or almost blank areas at the most black and most white extremes. Generally speaking, you pull the black and white pointers slightly toward the middle of the graph. This distributes the tones across the entire available brightness range, and usually improves contrast; then adjust the gray pointer to see if you can improve mid tones. This can work absolute miracles on under- and over-exposed photos.

Levels/histogram controls update the appearance of your photo in real time, and you can play to your heart's content. One quick learning tool, if your program has an option to automatically adjust levels: Open two copies of the same picture. Adjust one with the automatic tool. Now see whether you can make the other one look better by manual level control. Once you've settled the histogram, you can adjust other lighting controls. Lightweight programs omit the graph, and just give you sliders for low, mid and high.

Color. How pink do you want it? The usual problem here is that the overall color balance of slides and negatives changes over time, since some colors (cyan) fade faster than others (red). Manual manipulation here is much trickier than with lighting, since you have six possible colors and three variables (brightness, hue and saturation) of each, typically adjusted by sliders. My wife, Linda, who does this for a living, can wade in and fiddle with all of the above. I usually do better with an automated color-correction function, common with consumer grade software, and tweaked specifically for aged originals. Some programs also offer an in- between approach that gives you a menu of several thumbnail variants of your photo, with different color balances, that you can select and further manipulate.