The Forms Outlet, Inc. - Design Tips: Scanning

Please see your scanning software documenation to learn how to adjust the following controls.

Scanned images, which are composed of pixels, are represented as bits and bytes (a byte equals 8 bits.) In addition, each pixel is represted by a bit-based number which is assigned a value in a color table. The number of bits assigned to each pixel is called color depth or bit depth.

When there is is only one bit of computer memory assigned to each pixel, only two values may be represented, usually black or white. When 8 bits are used to define each pixel, 256 color values are possible. When 24 bits are used for each pixel, 16.7 million colors are possible. We recommend you scan at 8-Bit for black and white (to account for shades of grey,) and at 24-Bit for full color.

The resolution of scanned images is described in terms of DPI (dots per inch.) The scanning resolution should be high enough for the use of the image, but not so high as to waste storage space. Most print work requires images at 300 to 600 dpi.

Do not scan at a higher resolution than the native resolution of the scanner (eg. Epson 2400 Photo's native resolution is right there in the name - 2400 dpi.) Scanning at a higher resolution can cause blurriness.

Adjust your scanning resolution if you want to enlarge or reduce that image size. For example, if you want an image at 300 dpi and at twice the original size, scan at 600 dpi.

TONAL RANGE FOR PRINT

A scanned image, when optimized for a computer monitor, may have a tonal range of 0% (pure white) to 100% (pure black.) When scanning for print, the tonal range must be adjusted for press conditions.

Dot gain (the phenomenon of halftone dots printing larger on paper than they are on films or plates, reducing detail and lowering contrast) will dictate a maximum value of about 85-92%, depending on the press conditions and paper stock. The tolerance of the platemaking process will dictate a minimum value of 3-5%. For a photo with full tonal range, you need to decrease the contrast in your scanning histogram.

MORE ABOUT COLOR IMAGES

Scanners and computer monitors use a color space called RGB (red-green-blue.) RGB is a system which combines red, green and blue light to make all colors. However, a printing press uses a different color system, called CMYK (cyan-magenta-yellow-black.) CMYK combines translucent inks on paper to make all the various colors. After you scan your color image into your imaging software (such as Photoshop,) you will need to convert the file from RGB to CMYK. See your imaging software documentation about the various options available to you. Different methods (for example, Undercolor Removal versus Gray Component Replacement) can have different results.