File formats explained

If you have created graphics for printing you may have saved them as .tif, .eps, bmp or .pict file formats. These are simply different ways of describing the instructions for the appearance of the graphic to the computer. When you are creating graphics for the web you can only save them in GIF or JPG.

Common Vector Formats

.wmf Microsoft uses the .wmf or Windows Metafile for basic graphics
.cdr CorelDRAW package produces this form by default
.cgm Computer Graphics Metafile also a common ClipArt format.

Other formats include

A list of common Vector Formats

Common Raster Formats

Microsoft coined the term Bitmap for it’s version of a Raster graphic format. This was designed to use in Windows programs, it
has a high quality but large file size and will not work on the Web

A format by Compuserve Graphics Interchange. Gifs present the graphic as an 8-bit image or less which means that it is restricted to using only 256 colours so is generally a very small file size. Because of the limited colour depth, GIF compression works best with images with large blocks of the same colour. Photographs saved in GIF format lose some of the colour quality.

Transparent gif
Sometimes you may want your graphic to appear as though it has no background or border of it’s own, as though it is a free standing object or floating on top of the page background. When a graphic is saved as a transparent gif, the pixels of the transparent section are set to a certain value and that value is associated with the colour NULL or clear. If you open a transparent gif in Paint Shop Pro you can see that the pixels which are supposed to be transparent have a grey and white checker box appearance.

For Web use
When saving a GIF file you will be given an option of “Interlaced” or “Non-interlaced”. Interlacing displays the image gradually in increasing detail as it is downloaded onto a web page. The image sharpens gradually as it loads.

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.jpg (jpeg in a Mac)
A compressed format by Huffman, the jpg format was originally designed for photographic images and work well compressing these types of images without too much loss of quality. A JPG can be up to 24-bit images and have the capacity to display millions of colours depending on the level of compression (image quality) you choose when saving the file. They are not as suitable for line-art graphics such as cartoons because the file size is larger than with GIF files and it can cause blurring around the edges.

For Web use
When saving an image in the .jpg format you will be given the option to save the file using either “progressive” or “Standard” encoding. Progressive encoding is similar to “interlacing” a GIF file.

Progressive encoding allows your audience to view the image as though it is slowly coming into focus.

Standard encoding means that the image will be revealed from top to bottom as it is downloaded.

.tif (or tiff) Tag(ged) Image File Format
This format was formerly owned by Aldus and is now claimed by Adobe Systems (who bought out Aldus). It is one of the most popular and flexible of the current public domain raster file formats. It's main strengths are a highly flexible and platform-independent format which is supported by numerous image processing applications because it was designed by developers of printers, scanners and monitors. Very high resolution but unfortunately, a very large file size.

Other formats include

A list of common Raster Formats

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