Scanner Jargon

To help you feel confident when faced with scanner jargon, here’s a glossary of terms commonly used in the world of document scanners…

Resolution

The number of pixels displayed per unit of printed length to represent a bitmap image. Usually, resolution is measured as dots per inch (dpi) or pixels per inch (ppi). 

Pixels

The smallest element that can be displayed on a screen or printer, in other words it’s the smallest picture element unit in an image. 

DPI

An acronym for dots per inch, a measurement of resolution. Higher the DPI higher is the scanned image resolution. 

LPI (Lines Per Inch)

A term used in printing as a measurement of the frequency of lines on a screen (usually ranging from 55-200). LPI refers to the frequency of the horizontal and vertical lines. 

PPI (Pixels Per Inch)

A measurement of the amount of scanned information. The finer the optics of the scanner the higher the scan resolution. PPI is equivalent to DPI. 

Preview

An operation that gets a rough image of a document for setting parameters and image analysis. 

Image Type

According to the contents of your documents, the image can basically be divided into three types:

  1. Line Art: The Line Art image type is used for documents containing lines, text and detailed drawings. If OCR (Optical Character Recognition) software is used for document management, the Line Art image type should be selected and the resolution be at 300 dpi or higher. When the original is a negative film, this type is unavailable.
  2. Grayscale: A grayscale image is composed of pixels with 8 bits (256-shades) and contains only white, black and intermediate shades of gray.
  3. Color Image: The Color Image type is used for images with continuous tones and with lots of gray shades or colors. Color photos contain more information than any other type of images, but they also occupy much more disk space and system memory.

Bit depth

Also known as pixel depth, it defines the number of bits used to represent each pixel in an image. It also determines how many colors every pixel in a bitmap can have. In other words, the depth of information recorded during the scanning process is limited by the chosen bit depth. 

Optical Resolution

This refers to the number readings taken from an original image within a given distance, as opposed to the subsequent increase in resolution (but not detail) created by software interpolation. 

Maximum Resolution (Interpolated Resolution)

The process of increasing the resolution of an image, with the help of a software, by the addition of new pixels throughout the image, the colors of which are based on neighbouring pixels. For example, to create another dot between adjacent dots of Red values 100 and 108, the new dot can be assumed to have red value 104, so the transmission is 100, 104, 108. The same is done for Blue and Green, and the image will look smooth and larger. 

Interface

Interface is the type of connection used. The four most common types are…

  • Parallel (uses 25pin connector, same port that a printer would use)
  • USB (short for Universal Serial Bus, common on newer computer systems)
  • SCSI (Small Computer System Interface, requires SCSI controller, very fast)
  • Firewire (Extremely fast IEEE 1394 connection, requires firewire card)

Image Size

A large image size will lower the system performance of your computer dramatically. The file size is affected by the selected area, file format, scaling ratio, resolution and the image type. The following table presents the detailed information (file compression is excluded):

Image Type Description
1-bit images Black and White Line Art
8-bit images Black and White or Color Image, 256 gray levels or 256 colors
24-bit images Color Image, Millions of Colors
32-bit images Color Image, Billions of Colors

File Formats

File format determines the structure of information to be saved in a file. Refer to the following information to obtain better performance:

File Format; Extension; Advantages:

TIFF; .tif; Efficient file size, can save color separations

EPS; .eps, .epsf; Can save duotone information, can save clipping path, can save color separations

PCX; .pcx; Used by most software applications

PICT; .pict, .pct; Has compact file size

BMP; .bmp; Used by most software

Targa; .tga; Can save alpha channel

JPEG; .jpg, .jpeg; Has the best compression ratio

Compression

Encoding the bits of information in an image file so that it takes up less space when stored. Compression results in little or no distortion. File compression falls into two general categories:

  • Lossy compression and
  • Lossless compression

Lossy compression 

Lossy compression assumes that some of the data in the image file is unnecessary and can be eliminated without affecting the quality of the image scanned. Typically this type of compression has ratios between 10:1 and 100:1.

The most popular lossy compression option is JPEG. JPEG stands for the Joint Photographic Experts Group, which developed the compression standard. JPEG compression ratio is selectable in the host software and ranges from 2:1 up to 40:1.

Lossless compression 

Lossless compression stores image data in a file without deleting information, that is, no loss of image details, color or output quality.

If the 2:1 compression ratio is enough, lossless compression can to be considered.

The next step in your document scanning journey is choosing the right scanner that fits your requirements.

 

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