File Formats and Vector Graphics

File Types Images and data are stored in files. Each software application uses different native file types and file formats. Each file type has specific uses and restrictions

Bitmap Images and Vector Graphics A bitmap image is stored as individual square pixels, each defined as a specific color. The number of pixels per inch (ppi) is a measure of the image resolution when displayed on the screen. A bitmap file contains an image in one of various bitmap formats, such as TIFF, GIF, JPEG and BMP.

The most common file formats for bitmap images are JPEG and GIF files. A bitmap file always contains RGB data. Bit mapped images can get “jaggies” when the image is enlarged because the image is composed of colored square pixels.

Vector graphics represents images as mathematical formulas that define all the shapes in an image. A vector graphic image is composed of lines and a few control points that are connected using Bezier curves. Vector images are more flexible than bit-mapped graphics. Vector Graphics Image

Vector graphic images retain their sharpness and shape even when scaled to different sizes. Vector images are commonly created and used in Adobe Illustrator, Corel Draw and Macromedia/Adobe Freehand.

JPEG – Joint Photographic Expert Group Used primarily for photographs, graphic images. Most common format to store and transmit images on the web. Supported by all browsers. File saved in JPEG format has a compression algorithm applied to the image, throwing out bits (but we do not notice the differences). Each time an image is saved, more bits are lost. Save JPEG file only ONCE in image editing programs. Standard in lossy compression. Does not convert well to GIF format.

GIF – Graphical Information Format Originally created by Compuserve to send images across the internet. No de facto file format at the beginning of the web, GIF became the standard for file transmission since it included a compression factor for easy file transmission. Limited to high contrast images, simple images, line drawings, text, logos, clip art, and lots of single color areas. Lossy compression. Saves transparent background.

PNG – Portable Network Graphics Lossless compression, designed primarily for use in Flash, Corel Draw, MSPaint, and Fireworks. Designed to replace GIF and TIFF, but did not happen. Better compression than GIF. Supports transparency in an image (in other formats transparencies turn opaque).

TIFF – Tagged Image File Format Used in InDesign or Quark production images. Most popular for prepress images. Platform independent; supported by numerous image processing applications. Standard in document imaging; most accepted file type for printing.

Cannot be embedded into a web page. Owned by Aldus which later merged with Adobe. Lossless (resulting in larger files); some versions of TIFF have compression algorithms applied to final image. No provision for storing vector graphics or animation.

EPS – Encapsulated Postscript File InDesign or Quark production images. Used in print production applications. Files are very large. Takes lots of time to render image. Image in EPS cannot be modified. Image preview before printing is shown as JPEG file.