Design resources

File Formats

Confused by a particular file type - see my overview below.

• BMP - This is the Microsoft Windows bitmap format. It's a fairly compact (compression is optional, but usually turned on) format for images up to 24 bit. BMP is the native bitmap format for the Windows environment.

• EPS - Gives excellent quality images, although much larger than tiffs. can be imported into Quark.Encapsulated Postscript is a flavour of Postscript (see below) which can be included in other documents - if your software supports it.

• GIF - Graphics Interchange Format is a very efficient, and still quite popular picture format. There are two flavours of GIF, the old 87 and the newer 89a. 89a adds several extra features like transparency (so background graphics can "show through" the GIF in places) and animation. GIF animations are a very popular form of Web multimedia, because they're small and display on all current graphical browsers without needing a special plug-in or taking up much CPU time. Unfortunately, GIF pictures can only have 256 colours, or 256 shades of grey. 256 greys is photo quality so GIF is fine for any monochrome image, and 256 colour looks OK for many pictures, but it's no use for professional imaging. GIF images can also be interlaced, so that you can see a low resolution version of the picture before downloading very much of it. GIF interlacing has four passes, which show one out of every eight lines, then another eighth of the image, then another quarter, then the remaining half. GIF is a data-stream type format, like JFIF, so you can view partially downloaded images whether or not they're interlaced - without interlacing, a 25% downloaded picture gives you the first 25% of the lines, starting at the top.

• IMG - See "PIC".

• JPEG / JFIF - The JPEG (Joint Photographic Experts Group) File Interchange Format, commonly called JPEG and with the filename suffix .JPG, can be the most efficient image storage method of all - at a price. The idea of JPEG is that as it compresses the data it throws some of it away - technically, this is called "lossy compression". You can configure how lossy you want your JFIFs to be (well, you can if you're using photoshop); 100% quality gives you almost exactly the same result as the original picture but also gives you a gigantic, uncompressible file. 10% quality takes up much less space but looks dodgy. You have to strike a balance. JFIF can store up to 24 bit colour, so it's suitable for professional use, and it can do interlaced display like GIF (called "progressive" JFIF), which along with its small file sizes makes it the standard format for Web graphics. Like GIF, JFIF is a data-stream format - you can view images before you've got all of the data. Also like GIF, JFIF supports interlacing. The JFIF format also supports CMYK (process colour - Cyan, Magenta, Yellow and blacK in a subtractive colour model, as against the additive Red, Green and Blue more commonly used) images, which makes it suitable for use in publishing applications. CMYK support was added in a later version of the standard, though. This means that quite a few Web browsers, do peculiar things when fed CMYK images. There's no reason to use CMYK JFIFs unless you're sending the image to a CMYK output device, which a monitor isn't. Usually, CMYK ones get through because someone's converted a CMYK image of some other format, like TIFF, without changing the colour model.

• PCX - The ZSoft Paint format, occasionally suffixed .PCC, is ancient but still fairly widely used, simply because everybody understands it. There are three common versions, 0, 2 and 5; 0 is the original two colour one (small but not useful), 2 only does 16 colours and is hence also of little interest, and 5 does 24 bit. All are large for what they do, but fast to load on elderly computers. PCX is the IBM equivalent of Amiga IFF.

• PICT - Pict is the all-in-one Apple Quickdraw metaformat. It can include bitmapped or vector images, and can use different compression schemes.

• PNG - The Portable Network Graphics format, pronounced "ping", was created as a free replacement for GIF, whose LZW compression is owned by Unisys and which can't be included in commercial software without paying license fees to the owners. It handles 1 to 48 bit images, and is a lossless, well-compressed format like GIF. It still isn't very popular, though.

• PS - Adobe Systems' Postscript isn't an image format, per se - it's a page description language, originally conceived so computers could send very accurate page descriptions to the then-new high resolution laser printers. You can save black and white or even colour pictures as Postscript, but you'll end up with a very large file.

• PSD - Adobe Photoshop's native format, which stores all of its layer and selection and miscellaneous other image data.

• TIF - TIFF (to give the full acronym) stands for Tag Image File Format. TIFF was a large, unwieldy, 24 bit format until version 6 came out, which supported compression and made it less painful. TIFF is, nonetheless, a very popular professional graphics format that is accepted by Quark.