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 im-
ages without using interpolation. Using actual image data instead of interpolated data results in more
accurate images.
2 x 2.5 inch
image scanned
at 1200 dpi
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.
24-bit RGB (8 bits per pixel, per color)
36-bit RGB (12 bits per pixel, per color
48-bit RGB (16 bits per pixel, per color)
Scanner Technical Brief—Page 2
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.
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.
Scan mode
Bi-level (1 bit per pixel)
8-bit gray scale
10-bit gray scale
8-bit color (indexed color)
Number of colors recognized
2
1
= 2 colors (black and white)
2
= 256 shades of gray
8
2
10
= 1,024 shades of gray
2
= 256 colors
8
2
24
= 16.7 millions colors
2
= Over 68 billion colors
36
2
48
= Over 250 trillion colors
6/07
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