For black and white images, there are 256 levels of gray pixels: 0 (black) through 255 (white). With color images, each pixel can be one of 16 million different colors (with a good scanner). The more pixels, or “dots,” per inch, the higher your image resolution will be. pixels per inch or ppi) but is more commonly referred to as dots per inch (dpi).
Resolution is the number of pixels in a linear inch (i.e. Pixels are nothing more than very tiny colored squares (there are 72 pixels in an inch) that you can see if you increase the magnification of any image:
Once you scan an image, it becomes digitized-made up of hundreds of thousands of pixels. Through desktop publishing technology, however, anyone can now reproduce photographic images digitally (through scanning), edit and enhance the images (in Photoshop or any image editing app), and place the images as digital halftones in desktop publishing programs such as QuarkXPress and InDesign. Printers will charge about $8-10 per image to reshoot your photographs and create halftones. Traditional halftoning techniques, however, are costly. To compensate, printers have developed the process of halftoning where each individual photograph is reshot through a screen, resulting in an image composed of patterns of different sized dots that trick the eye into seeing continuous shades of gray: A printing press applies ink one color at time (per head on the press), and as such, it is not feasible to apply every shade of gray needed to create a realistic representation of the image. A black and white photograph, for example, is actually made up of black, white and infinite shades of gray. Halftones are used to reproduce continuous tone images, such as photographs, on a printing press.
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