IMAGE FILE FORMATS

1
POPULAR FILE FORMATS

2
GIF (GIF87A, GIF89A)

▪ Graphics Interchange Format (GIF) devised by the UNISYS Corp. And Compuserve, initially for
transmitting graphical images over phone lines via modems.

▪ GIF standard is limited to only 8-bit (256) colour images, suitable for images with few distinctive
colours (e.g., graphics drawing)

▪One byte per pixel

▪GIF reduces colors to 256 (256 from 224 colors)

▪ Uses a colour map of 256 possible RGB values, contained in file. Only the 8 bit index is
transmitted for each pixel that contains the closest match color to the original one.

▪Supports interlacing. - successive display of pixels in widely-spaced rows by a 4-pass display

1. GIF87a: The original speciation.

2. GIF89a: The later version. Supports simple animation via a Graphics Control Extension block in
the data, provides simple control over delay time, a transparency index, etc.

▪Compression ratio is close to 3:1. Color table is transferred to the receiver.

▪Provides support for animation - multiple pictures per file.

▪Provides one dimensional interlacing dividing the image into 4 groups: first contains 1/8 of the image,
second –1/8, third – ¼, last – 1/2.

▪This is patented technology

4
JPEG / JPG
•JPEG: The most important current standard for image compression.

A standard for photographic image compression created by the Joint Photographics Experts
Group

• Takes advantage of limitations in the human vision system to achieve high rates of compression.

•JPEG allows the user to set a desired level of quality, or compression ratio (input divided by
output).

• Lossy compression which allows user to set the desired level of quality/ compression.

5
6
 PNG
▪Portable Network Graphics (PNG)

▪The PNG format is intended as a replacement for GIF in the WWW and in image editting.

▪GIF uses LZW compression, which is patented by Unisys. All uses of GIF may have to pay royalties to Unisys
- PNG contains no patented technology.

▪PNG uses unpatented zip technology for compression

▪Provides transparency using alpha value.

▪2 Dimensional interlacing.

7
▪ Support for up to 48 bits of color information | a large increase.

▪ Files may contain gamma-correction information for correct display of color images, as well as alpha-
channel information for such uses as control of transparency

▪Figure: PNG of a single toucan overlaid to create a single picture. Notice how the shadows are overlaid
on lower toucan.

▪PNG supports multiple image layers, and adds an alpha byte to the RGB bytes to describe how to
combine each pixel with pixels from other layers or other images, ranging from totally transparent to
totally opaque.

8
COMPARISION BETWEEN JPG VS PNG

9
TIFF
• Tagged Image File Format (TIFF), stores many different types of images

(e.g., monochrome, greyscale, 8-bit & 24-bit RGB, etc.) –> tagged

• The support for attachment of additional information (referred to as \tags") provides a great deal of
flexibility.

• Developed by the Aldus Corp. in the 1980’s and later supported by the Microsoft

The most important tag is a format signifier: what type of compression etc. is in use in the stored image.

• TIFF is a lossless format (but now a new JPEG tag allows one to opt for JPEG compression).

• It does not provide any major advantages over JPEG and is not as user controllable it appears to be
declining in popularity

10
EXIF ( NOW NEF)
▪ (Exchang Image File) is an image format for digital cameras:

1. Compressed EXIF _les use the baseline JPEG format.

2. A variety of tags (many more than in TIFF) are available to facilitate higher quality printing,
since information about the camera and picture-taking conditions (flash, exposure, light source,
white balance, type of scene, etc.) can be stored and used by printers for possible color correction
algorithms.

3. The EXIF standard also includes specification of file format for audio that accompanies digital
images. As well, it also supports tags for information needed for conversion to FlashPix (initially
developed by Kodak).

11
SYSTEM DEPENDENT FORMATS
Many graphical/imaging applications create their own file format particular to the systems they are
executed upon. The following are a few popular system dependent formats.

Microsoft Windows: BMP

Macintosh: PAINT and PICT

X-windows: XBM

PSD

12
Microsoft Windows: BMP

• A system standard graphics file format for Microsoft Windows

• Used in PC Paintbrush and other programs

• It is capable of storing 24-bit bitmap images

Macintosh: PAINT and PICT

• PAINT was originally used in MacPaint program, initially only for 1-bit monochrome images.

• PICT format is used in MacDraw (a vector based drawing program) for storing structured
graphics

13
GRAPHICS ANIMATION FILES
• FLC – main animation or moving picture file format, originally created by Animation Pro

• FLI – similar to FLC

• GL – better quality moving pictures, usually large file sizes

14
POSTSCRIPT/ENCAPSULATED POSTSCRIPT
Postscript is an important language for typesetting, and many high-end printers have a Postscript
interpreter built into them.

• A typesetting language which includes text as well a vector/structured graphics and bit-mapped
images

• Postscript is a vector-based picture language, rather than pixel-based: page element definitions are
essentially in terms of vectors.

• Used in several popular graphics programs (Illustrator, FreeHand)

• Does not provide compression, files are often large

• Encapsulated Postscript les add some additional information for inclusion of Postscript les in
another document.

15