GRAPHIC DESIGN IMAGE FORMATS

 

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 flavor 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 flavors 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 colors, or 256 shades of gray. 256 grays is photo quality so GIF is fine for any monochrome image, and 256 color 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".

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 color, 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 color– Cyan, Magenta, Yellow and  blacK in a subtractive color 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 color model.

JPG – See JFIF and SPF.

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 color one (small but not useful), 2 only does 16 colors 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.

PDF - Short for Portable Document Format, a file format developed by Adobe Systems. PDF captures formatting information from a variety of desktop publishing applications, making it possible to send formatted documents and have them appear on the recipient's monitor or printer as they were intended. To view a file in PDF format, you need Adobe Reader, a free application distributed by Adobe System

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 color 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.

Bit depth – When an image is described as "x bit" with x being some number or other, what's being talked about is the number of colors. In bitplane or raster graphics, each pixel has its color described by a string of bits, and the more bits there are per pixel the more possible colors there are. The number of colors equals two to the power of the bit depth, so one bit (or "one bitplane") files can have only two colors, two bit can have four colors, three bit has eight colors and so on. The most common depths are 8 bit (256 colors) and 24 bit (16.8 million colors). Bit depths higher than 24 provide a wider color"gamut", so image manipulation software can pull out otherwise invisible detail out of the image.

Bitmapped file – Bitmapped files, also known as raster files, contain graphics information described as pixels, such as photographic images. The image is built up dot by dot; if you zoom in, the pixels get bigger and the image ends up looking like Lego.

Compression – Data compression is not a new concept – it's been around in one form or another for decades. If an image format includes data compression, then generally speaking the images will be smaller in size but take more computing power to load, as the computer has to work out what the original data was. In the olden days, compressed formats weren't popular because processors were too slow to display compressed images quickly. This, plus modern advances in compression technology, explains why older image formats tend to be bigger.

Dithering – What do you do if you have to display an image with lots of colors on a screen without enough to show it properly? You do dithering. This involves mixing pixels of the colors you have so that the end result looks more like the color you don't have. It's not as good as having enough colors to show the image properly, but it's better than the "banding" that results from doing a best-match sort of display.

Lossy compression
– A form of compression in which some data is discarded to allow much smaller file sizes. In image compression, lossy techniques such as those uses in the JFIF format

Metafiles – These are files that may contain either bitmapped or vector graphics data.

Page Description Languages – PDLs, as they're more often called, are used to describe the layout of a printed page of graphics and text. Two examples are Postscript and HPGL (the Hewlett Packard version). They're used almost exclusively in desktop publishing, most often as the file format sent from the computer to the printer.

Palette – The number of colors on screen is not necessarily the same as its palette. The palette is used in the same sense as a painter's palette; it holds all the colors that can be used, from which the ones that actually are used are chosen. A given video card might, for example, allow you to display 256 colors at a time from a palette of 32,768.

Pixel – The smallest element of an image, and the unit in which its resolution is expressed. The normal resolution of VGA graphics is 640x480 pixels; such a screen has a total of 307,200 pixels. A low resolution 320x200 image has only 64,000 pixels; a high res 1024x768 image has 786,432.

Raster file – See bitmapped file.

Vector file
– Bitmapped files describe a picture in terms of pixels, while vector files describe it in terms of geometry or lines. A line here, a curve here, this area filled with this color, and so on. Vector files are much smaller for an image of a given detail level and they can be magnified as much as you like without turning into giant pixels as well as not loosing any quality in the image.


Best Use Of Files When Used With Specific Applications

BMP
Screen display under Windows
Windows Wallpaper

EPS Or Vector Art
Printing to PostScript printers/Imagesetters
High resolution printing of illustrations

GIF
Screen display, especially the Web
Online publishing of photographic images

JPEG, JPG
Screen display, especially the Web
Online publishing of photographic images

PICT
Screen display on Macintosh or printing to non-PostScript printer

TIFF, TIF
Printing to PostScript printers
300 dpi at size high resolution printing of images

WMF
Screen display under Windows or printing to non-PostScript printer
Transfer vector images via the clipboard



E-mail: david@studioxagency.com