Epson Personal Document Station Technical Brief (Scanners) - Page 2

Image Quality-Resolution (cont.) 3. Interpolated resolution: Interpolation is a method to increase the resolution of an image. It uses a complex algorithm to "add" pixels to an image based on the mathematical probability of surrounding pixels. For example, if a scanner has a hardware resolution of 1200 x 2400 dpi, and a maximum resolution of 9600 x 9600 dpi, the scanning software uses interpolation to create scanned images with resolutions greater than the hardware resolution. 4. Benefits of higher optical resolution: Higher resolution allows you to scan the following types of images without using interpolation. Using actual image data instead of interpolated data results in more accurate images. Line Art When scanning black and white line art, image pixels translate exactly to the printed dots. Therefore, high resolution is required to capture and print the sharp lines and edges of an image. 2 x 2.5 inch image scanned at 1200 dpi If enlarged to 8 x 10 inches, effective resolution: 300 dpi Enlarging a small original In order to capture enough detail to enlarge an image, you must increase the scanned resolution in proportion to the increase in image size. If you don't, then you will have to interpolate image data to maintain the same resolution in the larger image. Precise pixel editing Many graphic artists scan images at high resolutions for precise pixel editing. It is always better to capture the image data when the image is being scanned and use true image data than to use interpolation if more data is needed later. Image Quality-Pixel depth Pixel depth refers to the number of bits of data captured for each picture element (pixel). Each pixel can have two states (On or Off); therefore the number of colors or gray scales that a scanner can recognize is computed by taking the pizel depth as an exponent of two. The following charts lists the number of colors recognized for each different scan mode. Scan mode Number of colors recognized Bi-level (1 bit per pixel) 21 = 2 colors (black and white) 8-bit gray scale 28 = 256 shades of gray 10-bit gray scale 210 = 1,024 shades of gray 8-bit color (indexed color) 28 = 256 colors 24-bit RGB (8 bits per pixel, per color) 224 = 16.7 millions colors 36-bit RGB (12 bits per pixel, per color 236 = Over 68 billion colors 48-bit RGB (16 bits per pixel, per color) 248 = Over 250 trillion colors Scanner Technical Brief-Page 2 6/07