Demystifying the black art of scanning. 2_1_1001.xml hed: From pix to pixels dek: Demystifying the black art of scanning. blurb: Demystifying the black art of scanning. number of pages:2 by Joe Farace
In the not-too-distant past, anyone who could use a scanner to produce a clean, sharp, full-range digital image from a slide or photograph was considered a guru. The reason is that while scanning hardware was always capable of producing the best possible scan for its particular design, scanning software lagged behind. Getting usable scans out of original images required intuition, ability, and lots of experience.
All that began to change as high-end scanners developed software that would automate many of these manual functions to help increase productivity and throughput. It didn’t take too long for mid-to-low-end scanners to start bundling software that made it possible for anyone to make the kind of scans that once required digital alchemy.
General scanning tips
There are two big myths about making great scans: The first is that the process is so difficult that it is beyond the capabilities of the average computer user. The second is that it is really easy to make a great scan. Of the two, the second is closer to the truth than the first. The real secret–if there is any secret beyond practice, practice, practice–is to examine all the options presented by scanner software and make decisions appropriate for the output you want to produce. The process starts with the hardware, but doesn’t stay there long.
Resolution: If you plan to use the original image or artwork in multiple applications, digitize at the highest resolution. This is usually referred to as the scanner’s optical resolution and is rated in dots per inch (dpi). If you plan on using the scanned image for the Web, you can scan at smaller sizes and lower dpi than you would for output to a large-format ink-jet printer.
Interpolated resolution: Less expensive scanners sometimes offer the option of scanning at resolutions higher than the hardware permits, which is called enhanced or interpolated resolution. While this sounds like something for nothing, digitizing at twice the scanner’s optical resolution can produce acceptable results. One way to improve interpolated scans is by using Adobe Photoshop’s Unsharp Mask command, which adds edge definition and crispness. If your favorite image-editing program lacks this option, Nik Multimedia’s Sharpener Pro works with any image-editing software that accepts Photoshop-compatible plug-ins (and that’s most of them).
Sharpening: Almost all digital images need some kind of sharpening, whether you use tools built into the scanner driver, image-editing software, or a third-party plug-in. To minimize the creation of artifacts, or pixelized areas in the image (caused by conflicts between various tweaks), apply sharpening only after you have done everything else.
Color mode: It sounds obvious that you should scan color images in color, but it’s also a good idea to scan black-and-white photographs using the driver’s color setting, which lets you pick up subtle tones in parts of the image. You can always convert it to grayscale later using your image-editing program.
Scanning film: A clean original means less retouching later, so it’s a good idea to keep a can of environmentally friendly air near the scanner to blow dust particles off slides or negatives. Keeping your negatives and slides clean is more important with film scanners than flatbeds. Because of the small original size, even the tiniest dust speck can end up looking like a boulder in the final scan.
Eliminating moiré: Most flatbed scanners are capable of digitizing prints and artwork in a single pass, but when scanning pages from books, magazines, or other printed sources you may run into strange patterns caused by the dots or lines used in printing these images. One of the best ways to eliminate these annoying patterns is to use the scanner’s three-pass mode-if it has one. If that doesn’t work or your scanner lacks this capability, rotate the image slightly before scanning. You can always use your image-editing program’s Free Rotate command to straighten it later, although scanner software from companies such as Epson do this automatically.
Adobe Photoshop tips
Many scanner drivers are Acquire plug-ins or TWAIN modules that install in cross-platform image-editing programs such as Adobe Photoshop and let you access scanner hardware via the program’s Import menu. These drivers, or acquire modules, are typically found under File in the Import menu. Driver software bundled with most flatbed scanners, such as Agfa’s ScanWise, pretty much does all of the work for you. All you have to do is select the kind of original and set the size and final resolution, and the software will produce an acceptable scan. No matter what kind of software you use to acquire the image, set it to the approximate size and resolution at which it will ultimately be used–whether inserted into a desktop published document, used on your Web site, or printed with a desktop ink-jet printer.
If you want to improve the scan, there are a few things you can do to improve newly digitized images.
The first thing I do with any fresh scan is use Photoshop’s Levels command to set highlight and shadow points. Under Image, choose Adjust and select the Levels menu, which presents you with a histogram showing the image’s range of darkness and brightness. At the ends are black and white triangles, and in the middle is a gray one. They can be moved back and forth under the histogram’s peaks and valleys to interactively enhance the image. The Levels dialog box includes Eyedropper tools that let you click on equivalent color tones in the image to adjust white, gray, and black points. To correct off-color originals, often all you need to do is click on a point that should be white (or black or middle gray) to bring the image into balance. You can also set specific output values. Some photographers like to set the highlight at 5 to provide some detail and set the shadow at 250 to produce shadows that are not dense black.
When you’re finished, it’s time to sharpen the image using the Sharpen command (not the best way) or the Unsharp Mask function (much better), but be careful not to oversharpen–this can create decidedly ugly, pixelized images. One way to keep from oversharpening is to use Photoshop’s Fade (under Edit) command to back off the amount of sharpening until a highly enlarged (use the Magnifying Glass tool) portion of the image shows that the jaggies are gone.
You have the choice of doing all of this work after you’ve captured the image, or doing it before by using third-party acquisition software, such as the Photoshop-compatible plug-in SilverFast from LaserSoft International. SilverFast, which is available in versions compatible with many scanners, allows its controls to be moved to a second monitor, permitting the resizable image preview to fill your main monitor. The plug-in’s Prescan feature lets you freely rotate and resize the image before it’s acquired. A ScanPilot feature automatically guides digital newbies step-by-step through the process of making individual image corrections. All operations are done in real time, allowing you to see the effect of any changes you make so that unwanted modifications can be undone. Beginners can take advantage of built-in presets and auto-adjust features, while experienced users can monitor exact values using SilverFast’s built-in densitometer. SilverFast lets you define and match input and output color spaces using International Color Consortium profiles and is compatible with color-management systems such as ColorSync for the Mac OS and ICM for Windows.
Even Adobe’s inexpensive Photoshop Elements program contains some features that improve scans. The Straighten and Crop Image command (under Image, choose Rotate) automatically fixes crooked digital files that are accidentally produced when the original moves slightly after the scanner’s lid is closed. If you can work in this RGB-only environment, you’ll find that Elements has many image-tweaking features, and supports Photoshop-compatible plug-ins. For instance, while Elements lacks the Levels command found in Photoshop, you can use an Adjustment Layer (under Layer, choose New Adjustment Layer and select Levels) that provides similar controls. Photoshop has an identical function found in the same menu hierarchy.
Paint Shop Pro
Jasc’s Paint Shop Pro is a Windows-only image-editing program that gets better with each update. Version 7 is the latest iteration of this amazingly flexible program that combines aspects of Paint, Draw, and Web-design software with image enhancement. Users familiar with Photoshop’s uncluttered look may be a bit put off by PSP’s slightly busy interface, but the use of floating palettes, which spring open when you drag a mouse across them, helps keep things tidy.
Scans are accomplished under File Import by choosing the Twain menu, where you’ll also find capture capabilities for digital cameras and screen capture. Once a scan has been made, you’ll find some handy commands in the Enhance Photo menu under Effects. You’ll find automatic commands that can adjust color balance, contrast, and brightness. Like similarly named commands in Adobe Photoshop, these work with some images, but not all. When scanning images from magazines or books, you will find the Moiré Pattern Removal control especially useful. Rather than just a “click and hope”-style command, you get a small dialog box with Before and After preview windows, along with a small toolset that lets you eliminate those annoying patterns. Got a few dust spots? Try the Salt and Pepper filter (under Effects, choose Noise) that can eliminate black or white dust specks without making the image look like mush. Before and After windows help you keep your perspective. Automatic Scratch Removal (under Effects, choose Enhance Photo) will do a comparable job with scratches on images from film scanners.
Overall effects similar to Photoshop’s Levels or Curves can be found under Layers in the New Adjustment Layer submenu. This submenu gives you access to many tools that have slightly different interface and can be adjusted as I described in the previous section.
To find something that truly resembles Photoshop’s Levels function under Color select Histogram Functions.
While some of the controls are similar to Photoshop’s, PSP’s Histogram controls are more comprehensive, while providing an interface that will probably be less intimidating for new computer users. My favorite part of PSP’s Histogram dialog box is the Midtones Compress slider that manipulates the whole curve while providing a direct view of any part of the image. Also bundled with the program is a copy of Jasc’s Animation Shop 3, which will be useful for Web designers but not necessarily for those seekers of the perfect scan.
Paint Shop Pro includes many useful image enhancements and manipulation filters, and is compatible with the Photoshop plug-in standard, although there is no designated plug-ins folder. After you get a plug-in installed, it appears at the bottom of the Effects menu as a “Plug-in Filters” submenu.
There are many useful plug-ins that can help improve the quality of scans, including Vivid Details Test Strip 3, which expands on the previous versions by offering a Metamorphosis feature that prevents you from overcorrecting images. This can be a problem for two reasons: When using all of the program’s (and this applies to all image-editing software) controls to adjust brightness, contrast, and color, it’s easy to make corrections that overwrite other corrections. Obviously, this decreases productivity, but it also compounds the rounding errors that occur when any digital image is being tweaked. The fewer corrections you make, the fewer the rounding errors, which results in cleaner, purer image files. The Metamorphosis feature of Test Strip presents you with two versions of your image; you simply pick the one you like most by clicking it. This can take a pale scan and tweak the colors and contrast faster than any menu or command in any program, without danger of overcorrecting.
Deneba’s Canvas is a Web design, Paint, and Draw program that includes image-editing features. As I was finishing this story, Deneba launched version 8 of the program, which is currently available only for Windows. A Mac OS version is expected by the end of the year.
You’ll find an Image menu that includes an Acquire submenu, giving you access to TWAIN-powered scanning devices. Rather than scanning images that are themselves a file, anything acquired by a scanner becomes part of a Canvas document. Even something simple like cropping is somewhat more complex than using any image-editing program out there, however.
Once an image has been scanned, you’ll find only a few commands that can be used to maximize image quality, though there are familiar favorites such as Despeckle and Dust and Scratches (under Image, choose Filter and select Noise). An Unsharp Mask command is found under Image in the Filter menu by choosing Sharpen. It can be used to improve the quality of scans made at interpolated resolutions. Serious adjustments can be made by using the controls found under Image in the Adjust menu. Here are the eminently useful Levels and Curves, as well as five different kinds of color controls, including Hue/Saturation. If the interface of these adjustments appears less extensive that Photoshop’s, chalk it up to a weak interface design (maybe the Mac OS version will look better) because all of the controls except the indispensable Eyedropper tools are present in the Levels dialog box.
Canvas 8 is compatible with Photoshop plug-ins such as Extensis’s Intellihance Pro. Intellihance Pro 4 includes presets for flatbed and drum scanners (not film scanners), and you can use these presets as a starting point before using the plug-in’s pop-up menus for adjusting saturation, color cast, and sharpness to tweak the image while you watch the changes on a large preview window.
As you can see, scanning may not be the turnkey approach hardware manufacturers tell us it is. But the process is far less complex for the average computer user thanks to software bundled with the scanner and programs like Adobe Photoshop, Jasc Paint Shop Pro, and Deneba’s Canvas. Choose the program that fits your specific application and budget, and blend in a few useful plug-ins. You will find that the ability to create clean, sharp, color-balanced scans is not only limited to gurus.