Mastering the Controls of Scanner

Even the most simple scanner interfaces may have a bewildering array of controls for the beginner. Your first step should be to read the manual furnished with your scanner, whether it’s a printed booklet or a glorified Help system copied to your hard disk. Scan the text until you understand the following controls:
- Brightness/Contrast: An adjustment for the relative darkness of an image and the number of tones available.
- Gamma: A control that allows you to compensate for the tendency of devices (such as computer displays and scanners) to represent tones in a non-linear way. You can even out bumps with the gamma control.
- Color Correction: Controls that let you keep your color accurate.
- Bit Depth Selection: The number of bits per pixels. Scanners scan in RGB color that is comprised of three channels per pixel. Therefore, a 36-bit scanner has a color depth of 12 bits per channel and a 2-bit scanner has a color depth of 14 bits per channel. Bit depth is also used in reference to the number of colors or tones captured by a scan. Black-andwhite images may be captured using 8 bits of information (256 different gray tones), whereas color images are captured using at least 24 bits of data (16.8 million colors).
- White Point and Black Point Adjustments: These controls let you tell the scanner which parts of your subject are the brightest and darkest areas, respectively, that contain detail.
- Histograms: These are charts that show you how many tones at each brightness level appear in an image. You can use them as tools for adjusting brightness and contrast.
- Sharpening: Scanners can presharpen images for you, although in most cases it’s more productive to carry out this step in Photoshop.
- Descreening: Scanners can remove halftone screens with some success, but you gain flexibility when you do this in Photoshop.
- ICC Profile Management: This control lets you specify the color characteristics of your devices.
- Resolution: This is one of the most important controls, as well as the one that is most often mishandled by scanning neophytes. Resolution is the amount of image detail captured by the scanner, measured in samples per inch (spi), but usually (and inaccurately) referred to as pixels per inch (ppi) or dots per inch (dpi).

Surprisingly, with resolution, more is not always better. Use too high a setting, and you end up with needlessly large file sizes. Use too low a setting, and you wind up with not enough detail. Although Photoshop allows you to reduce the size of large images (through a process called resampling), you’ll always lose a little (or a lot) of quality when you do this. Using the correct resolution for your applications, from Web display to desktop printing to professional color reproduction, is essential to Photoshop success.