Epson Perfection 640U Series Manual - Página 2

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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 colors (black and white)

= 256 shades of gray

= 1,024 shades of gray

= 256 colors

= 16.7 millions colors

= Over 68 billion colors

= Over 250 trillion colors

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