An image composed of shades of gray is described as grayscale. Often referred to as black and white, strictly speaking a true black and white image is composed only of black and white while a grayscale image has black, white, and various shades of gray in between black and white.
A traditional (non-digital) grayscale photograph may contain millions of shades of gray. Digital images can only store a limited amount of color data (sometimes very little, sometimes a lot). Information in a digital photograph is stored in bits. In a black and white 1-bit image each bit stores a value for either black or white. Digital grayscale images are typically 8-bit, containing up to 256 shades of gray ranging from 0 (black) to 255 (white). Instead of color information, the image file stores levels of brightness or intensity.
Working With Grayscale ImagesIn desktop publishing we often work with grayscale images, turning color images to grayscale when color printing is unavailable, colorizing images that are started out as grayscale, or combining color and grayscale pictures.
- Scanning Line Art explains how to scan line art as a 1 bit image, grayscale image, or a halftone and how each differs in appearance.
- The Many Faces of Black and White describes methods of converting color photos to grayscale using desaturation and other graphics software methods.
- Colorize B&W or Grayscale Clip Art has tips on ways to take a grayscale (or a 1 bit black and white image) and add color to it, including creating duotones.
- Combine a Color and Black & White Image is actually about taking a color photo and selectively keeping the color in certain areas while converting the rest of the image to grayscale.
- Grayscale Masks are often used in photo editing to protect areas of an image when applying filters or doing other photo manipulations. The grayscale mask uses the grayscale channel or alpha channel found in certain digital files.
Printing Grayscale ImagesPrinters cannot print continuous tones such as those found in non-digital photographs, including continuous tone grayscale photos. Instead, the printer simulates the look with halftones or dithering.
When using scanned images or images from a digital camera, you can produce digital halftones direct from the software to the printer. Digital halftoning depends on the LPI (lines per inch, or screen frequency) and the resolution of your output device (printer). The screen used may be specified in your printers PPD (PostScript Printer Driver) or set specifically in your software program.