What type of image format do I use?

Still Images - There are three classes of image file formats. Many if not all of these formats can be imported or opened in most graphics programs.

Bitmaps
Metafiles
Vector

Trade offs?
Motion File Formats

Bitmaps - A bitmapped (formerly known as raster) graphic is composed of a collection of tiny individual dots or pixels. The simplest bitmapped files are monochrome images composed of only black & white pixels.

TIF (Tagged Image File Format, or TIFF)

A standard file format for storing images as bit maps developed by Microsoft & Aldus. It is used especially for scanned images because it can support any size, resolution, and color depth. Since TIFFs are platform-independent files, they can be opened on both Macintosh and Windows graphics programs.

GIF (Graphics Interchange Format)

Is an ideal web format for drawings and graphics. Developed by CompuServe is a completely platform independent bitmap file format. It is automatically compressed and viewable on most web browsers. GIF is a lossless method of compressing a file through a simple substitution method. Therefore, the maximum compression available with a GIF depends on the amount of repetition in an image. A flat colour will compress well - sometimes even down to one tenth of the original file size - while a complex, non-repetitive image like a color picture will fare worse, perhaps only saving 20% or so. There are problems with GIFs. One is that they are limited to a palette of 256 colours or less. However, it is possible to have a transparent background.

JPEG (Joint Photographic Experts Group)

JPEG is the best compression format to use on color images and its dramatic file size reduction makes it ideal for posting images on the web. However, its compression technique is a bit extreme. Although it can reduce files sizes to about 5% of their normal size, some detail is lost in the compression. In other words, to save space it just throws away parts of an image. Depending on how much you want to compress the image the algorithm throws away the less significant part of the data (the smaller curves) which adds less to the overall "shape" of the image. This means that, unlike GIF, you get to say how much you want to compress an image by. However the extreme compression method can generate unwanted artifacts - like false colour and blockiness. Because of this it is not recommended for line drawings and graphics.

BMP (bitmap)

The bit-mapped file format used by Microsoft Windows.

PCX (Paintbrush)

Originally developed by ZSOFT for its PC Paintbrush program, PCX is a common graphics file format supported by many graphics programs, as well as most optical scanners and fax modems.

PIC (Lotus Picture File)

A relatively simple file format developed by Lotus for representing graphs generated by Lotus 1-2-3. PIC is supported by a wide variety of PC applications.

Return to Top

METAFILE - This multifunction file type accommodates both vector and bitmapped data within the same file. While seemingly more popular in the Windows environment, Apple's PICT format is a metafile.

EPS (Encapsulated PostScript)

A metafile format for graphics files that are designed to be imported into another application, such as a desktop publishing program. This file type contains two elements: the bitmapped image and the PostScript code that tells your printer or output device how to print the image. This is ideal for printing files that have both images and text in them. EPS uses a combination of PostScript commands and TIFF or PICT formats.

WMF (Windows Metafile Format)

A file format for exchanging graphics between Microsoft Windows applications. WMF files can also hold bit-mapped images. It’s a 16-bit metafile that can be used by Windows 3.x, Windows 95 and Windows NT to display a picture.

PICT

Developed by Apple Computer in 1984 as the standard format for storing and exchanging graphics files. It is supported by all graphics programs that run on a Macintosh and can be viewed in several Windows based programs. PICT files contain both bitmapped or object-oriented information.

Return to Top

VECTOR - A vector graphic is defined in terms of shapes. Each image file is represented by a mathematical description of the shapes that comprise that image. These graphics are sometimes called "object-oriented'. Vector-oriented images are more flexible than bit maps because they can be resized and stretched. Another advantage of vector graphics is that representations of images often require less memory than bit-mapped images do. Almost all sophisticated graphics systems, including CADD systems and animation software, use vector graphics. In addition, many printers (PostScript printers, for example) use vector graphics. Fonts represented as vectors are called vector fonts, scalable fonts, object-oriented fonts, and outline fonts.

POSTSCRIPT

A programming language created by Adobe Inc. That defines all of the shapes in a file as outlines and interprets these outlines by mathematical formulae called Bezier curves. Any PostScript-compatible output device, whether it's a film recorder or laser printer, uses the definitions to reproduce the image that's on your computer screen. This carries all of your font information, layout, colors, etc.

DXF (Data Exchange File)

A format created by AutoDesk. Almost all PC-based CAD systems support DXF.

FONTS

Many fonts are vector-based graphics. The best-known example of a vector font system is PostScript. Bit-mapped fonts, also called raster fonts, but must be designed for a specific device and a specific size and resolution. TrueType fonts are the most common and are supported by both Windows and Macintosh.

Return to Top

Tradeoffs between vector (metafile) and raster (bitmap) graphics?

Note that most output devices, including dot-matrix printers, laser printers, and display monitors, are raster devices (plotters are the notable exception). This means that all objects, even vector objects, must be translated into bit maps before being output. The difference between vector graphics and raster graphics, therefore, is that vector graphics are not translated into bit maps until the last possible moment, after all sizes and resolutions have been specified. PostScript printers, for example, have a raster image processor (RIP) that performs the translation within the printer. In their vector form, therefore, graphics representations can potentially be output on any device, with any resolution, and at any size.

Return to Top

Motion Files Formats - for Video & Animations

Motion JPEG

In this format, each frame of a video is compressed using the JPEG format. Many video editing software use a motion JPEG format because it allows for frame by frame editing.

MPEG (Moving Picture Experts Group)

Is generally produces better-quality video than competing formats, such as AVI & QuickTime. MPEG achieves higher compression rates than Motion JPEG because it compresses information across multiple frames by storing only the changes from one frame to another. However, this makes frame by frame editing difficult because so much information is thrown away. There are two major MPEG standards. MPEG-1 provides a video resolution of 352-by-240 at 30 frames per second (fps). This produces video quality slightly below the quality of conventional VCR videos. MPEG-2 supports resolutions of 720x480 and 1280x720 at 60 fps, with full CD-quality audio. This is sufficient for all the major TV standards, including NTSC, and even HDTV. MPEG-2 is used by DVD-ROMs. An MPEG-3 standard for HDTV was being developed until it was realized that MPEG-2 already met the requirements. MPEG-4, also referred to as MP3, is being worked on.

QuickTime

Is built into the Macintosh operating system and is used by most Mac applications that include video or animation. PCs can also run files in QuickTime format, but they require a special QuickTime viewer. QuickTime supports most encoding formats, including JPEG and MPEG.

AVI (Video for Windows)

Short for Audio Video Interleave, is built into all Windows 95+ operating systems. AVI files are limited to 320 x 240 resolution, and 30 frames per second, neither of which is adequate for full-screen, full-motion video. It supports several data compression techniques.

Animated GIF

A type of GIF image that can be animated by combining several images into a single GIF file. Not the best animation format, but has become extremely popular because it is supported by nearly all Web browsers. In addition, animated GIF files tend to be quite a bit smaller that other animation files, such as Java applets.

JAVA Applets

Developed by Sun Microsystems, Java is a programming that is well suited for the web. Java applets can be downloaded from the Web and run on a Java-compatible Web browser, such as Netscape Navigator or Microsoft Internet Explorer.  This makes it compatible on most platforms and operating systems.