BMP

DCX

Dithering

Exact Printing

Flate Encoding

JPEG

Lossless Compression

Lossy Compression:

Modified Modified Read Encoding

PCX

PDF

PNG

Run Length Encoding

TIFF

TIFF Group 3

TIFF Group 4

TIFF JPEG

TIFF Packbits

B

BMP: The Windows Bitmap file format is the standard file format used by Microsoft Windows. Bitmap files can contain either 2 (black and white), 16, 256 or 16.7 million colors. Most Windows Bitmap files are not compressed. The default file extension for Windows Bitmap files is .BMP.

D

DCX: The DCX format originally developed for Z-Soft is a multi-page format for PCX files. The default file extension is .DCX.

Dithering: is the attempt by an application to create a matching color from a mixture of other colors when the required color is not available. The result may appear somewhat grainy since it is composed of different pixel intensities rather than a single intensity over the colored space.

E

Exact Printing: The creation of fax images that look exactly as they do when printed to the local printer. Strategically positioned tables, tabs and page breaks remain as they should when sent as a faxed image. Also called ‘What You Print is What You Fax’, or WYPIWYF printing.

F

Flate Encoding: Ken - we need a simple definition for this.

J

JPEG: The JPEG (Joint Photographics Experts Group) format supports Palettized8 and RGB24 page types. It uses a method of compression that reduces image file size by selectively reducing the amount of detail contained in the image and by transforming the image data into a format that is better suited for compression. Images with fewer details compress extremely well, while pictures with a high degree of random detail do not compress as well, or suffer some degree of image degradation. The relative amount of detail removed can be specified in most applications. At the default value of 75, relatively little picture degradation takes place, but a significant amount of compression is obtained. At lower values , there is better compression, but with a loss of image quality. JPEG images are either true color or grayscale (256 shades of gray). The default file extension for JPEG files is .

L

Lossless Compression: A lossless compression method is one where no data is discarded during the encoding process. An image compressed using a lossless method is identical to the original image when uncompressed.

Lossy Compression: Lossy compression discards data during encoding. It is designed specifically to remove information that the human eye cannot easily see; for example, slight changes in color not perceived well by the human eye.

M

Modified Modified Read Encoding:: Ken we need a simple definition for this.

P

PCX: PCX files were originally developed for Z-Soft’s PC Paintbrush package. These files come in monochrome, 16 color, 256 color and true color (24-bit) varieties. PCX files are compressed using a method that offers a modest degree of compression compared to other compression formats. The default file extension for PC Paintbrush files is .PCX.

PDF: Portable Document Format (PDF) is a universal file format that preserves the fonts, images, graphics, and layout of any source document, regardless of the application and platform used to create it. This format, developed by Adobe Systems, Inc.

PNG: The Portable Network Graphics format was created as a free replacement for GIF. It handles 1 to 48 bit images, and is a lossless, well-compressed format like GIF.

R

Run Length Encoding: A simple compression method that uses repeated characters in a file. For example: aaaaabbbbbbbbbccccc is more concise if represented as 5a 9b 5c. Run-length encoding is quite useful for images as even more compression can be attained for image files.

T

TIFF: The TIFF format was developed by Microsoft and Aldus Corporation as a portable method of storing bitmap images. TIFF files come in monochrome, 16-color, 256-color, 16-color grayscale, 256-color grayscale and true color (24-bit) varieties. TIFF also supports g3 and g4 fax formats. TIFF files exist in both compressed and uncompressed formats. The compression format offers a high degree of compression. The default file extension for TIFF files is .TIF.

TIFF Group 3: A standardized file format that encodes image pages using Huffman G3 compression, as defined by CCITT and ITU fax standards. Each page is separately defined in the TIFF file. Offers very good compression of text, and good compression of bi-tonal images. Used extensively as a storage format for scanned black and white documents. Has the additional advantage that if one bit changes, you only lose the rest of the line.

TIFF Group 4: Popularized as the TIFF fax file format for next generation G4 fax cards and G4 fax machines. Very popular in Japan. Extremely good compression of text, but not so good at bi-tonal images (files can be larger than Group 3 files). Used extensively as a storage format for scanned black and white documents. Used by PDF files as the compression method for bitonal images. If one bit changes, you lose the rest of the page.

TIFF JPEG: Creates multiple 24 bit compressed images in one file. Image sizes can be very large, and there are only a limited number of viewers capable of viewing multi-page images.

TIFF Packbits: Original TIFF file compression format for bitonal and color images. Similar compression to PCX files. 24 bit color image compression is lossless, but images are very large.

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