http://ping.fm/vPiuT
About printing :-

Whether you are printing an image on your desktop printer or sending it to a prepress facility, knowing a few basics about printing will make the print job go more smoothly and help ensure that the finished image appears as intended.

Types of printing

For most users, printing a file means that the Adobe Photoshop application sends the image to an inkjet printer to print a photograph. Photoshop can send your image to a variety of printing devices to be printed directly onto paper or to be converted to a positive or negative image on film. In the latter case, the film can be used to create a master plate for printing by a mechanical press.

Types of images

The simplest types of images, such as line art, use only one color in one level of gray. A more complex image, such as a photograph, has color tones that vary within the image. This type of image is known as a continuous-tone image.

Halftoning

To create the illusion of continuous tones when printed, images are broken down into a series of dots. When printing photos on a printing press, this process is called halftoning. Varying the sizes of the dots in a halftone screen creates the optical illusion of variations of gray or continuous color in the image.

Note: Although inkjet printers also use dots to create the illusion of continuous tones, they use a different type of screen process that does not vary the size of the dots. Instead, inkjet printers use dots that have a uniform size and that are much tinier than the dots used by most printing presses.

Color separation

Artwork that will be commercially reproduced and that contains more than a single color must be printed on separate master plates, one for each color. This process is called color separation and most commonly uses cyan, yellow, magenta, and black (CMYK) inks. In Photoshop, you can adjust how the various plates are generated.

Quality of detail

The detail in a printed image results from a combination of resolution and screen frequency. The higher an output device’s resolution, the finer (higher) a screen ruling you can use. Many inkjet printer drivers offer simplified print settings for choosing higher-quality printing.
Printing images to a desktop printer-

Unless you work in a commercial printing company or service bureau, you’re probably printing images on a desktop printer–such as an inkjet, dye sublimation, or laser printer–and not to an image setter. Photoshop lets you control how your image will print.