Digital Graphics File Formats

Anna Malpas

Raster GraphicsRaster graphics, also known as bitmap graphics, are digital images that are composed of tiny rectangular pixels. Each pixel or dot displays a unique colour and together all of these coloured dots create an image. Every pixel in a bitmap is stored as one or more bits in computer memory. Raster graphics with a greater number of colours and pixels will require more bits and take up more memory. Typical file formats for raster graphics include .jpeg, .gif, .tiff, and .bmp.

Raster graphics are represented in a grid structure, the width and height are usually indicated by the number of rows and columns rather than a particular unit of measurement. The size of an image might be described as 640 x 480 meaning that there are 640 pixels in a row and 480 pixels in a column. The resolution or degree of sharpness present in an image is calculated by determining the number of pixels per inch (PPI) or dots per inch (DPI). A higher resolution raster graphic will have smaller pixels that result in a more detailed image. When raster graphics need to be displayed or printed at larger sizes, it is helpful to use a higher resolution so that the image does not appear grainy.

Vector GraphicsVector graphics use mathematical relationships between points on an image to describe that image and are more flexible and clear than raster or bitmap graphics. There are a limited number of pixels in raster images, which means that a larger image needs more pixels and a smaller image fewer pixels. However, a vector graphic does not have this limitation because of the mathematical relationships between point “A” and “B”. The mathematical relationship between the points is depicted as a path, or the line or curve that connects the two points.

An advantage of a vector graphic is clarity, no matter one size image. Unlike a bitmap image that uses a limited amount of pixels and can’t be enlarged without loss of quality, vector graphics do not have this problem. Since a vector graphic uses math to express the relationship between two points in paths, enlarging and reducing the picture will not usually result in a loss of clarity. This makes vector graphics ideal for use in typeface, line art and illustrations. They would be most suitable for a business logo since the graphics can be decreased to be printed on letters and envelopes and also enlarged for billboards with clear quality.

Raster Graphics

JPEGStands For Joint Photographic Experts Group

Used For/Example JPEG compression is widely used for images on websites and is supported by most editors, browsers and image viewers. Also used to compress and store images created by most scanners and digital cameras.

Advantage Files are small which means you can fit more images on a memory card. Open standard format can be universally viewed by most web browsers, computers and editing programs.

Disadvantage File is reduced to an 8 bit per channel image which can only represent 256 shades for each (red, green, blue) colour

TIFFStands For Tagged Image File Format

Used For/Example A common format for exchanging raster graphics (bitmap) images between application programs. TIFF files are commonly used in desktop publishing, faxing, 3D applications, and medical imaging applications.

Advantage Better quality than JPEG. They are good for images that will be heavily edited in an editing program. Also, TIFF files don’t lose any quality due to compression because they have the option of lossless compression.

Disadvantage File sizes are large so you can’t email them, and they won’t open on some devices.

GIFStands For Graphics Interchange Format

Used For/Example Used for short digital animations, often on the internet

Advantage Uses lossless compression, there is support fortransparency and they are suitable for small animations. It allows people to see moving images quicker than in a video file.

Disadvantage Image can only contain up to 256 colours which limits the resolution of the image.

BMPStands For Bitmap image file

Used For/Example BMP files are especially suited for the storage of real-world images, complex images can be rasterized in conjunction with video, scanning, and photographic equipment and stored in a bitmap format.

Advantage There is no loss in compression. Bitmap files may be easily created from existing pixel data stored in an array in memory.

Disadvantage They have a large file size, and are outdated and barely used.

Vector Graphics

PSDStands For Photoshop document

Used For/Example PSD file types fully support all the powerful features of Photoshop, such as layers, layer masks, adjustment layers, channels, paths, etc. When an image is opened in Photoshop, it temporarily converts it into a PSD file so it can be edited with Photoshop’s tools.

Advantage No loss in image quality no matter how many times you re-open and re-save a PSD, and it saves all of the layers, adjustment layers etc as part of the file, allowing you to go back any time and make changes to the image.

Disadvantage File sizes can be very large if there is a lot of layers, and PSD files can’t be opened unless someone has Photoshop.

AIStands For Adobe Illustrator Art

Used For/Example AI files are drawings created with Adobe Illustrator that are commonly used for logos and for print media. This collection of programs will enable you to easily open, edit and even convert AI format files.

Advantage Can be scaled large and small as the vectors have no loss in definition

Disadvantage Newer versions may have compatibility issues, not a standard file format

FLAStands For Flash file

Used For/Example Used to create animation and games

Advantage They can produce high quality files but with a small file size which makes them very suitable for the internet. The majority of PCs and Macs have the Flash plug-in required to play Flash files.

Disadvantage FLV is the Flash video file format. because it's not a common distribution format like Windows Media or QuickTime, you may find that you often have to convert files from other formats to FLV.

WMFStands For Windows Metafile

Used For/Example WMF is a file extension for a graphics file used with Microsoft Windows. WMF files can contain both vector and bitmap image information.

Advantage Can be scaled large and small as vectors have no loss in definition. WMF is a Windows standard format that works well with Office.

Disadvantage

File Format Capture and Optimising

CompressionDefinition File compression is commonly used to

make a file smaller which makes them easier to send from one computer to another over a connection that has limited bandwidth. This makes the sending of the file much faster

Advantage Compressing files allows you to store more files in the storage space you have available. Lossless compression, used in zip file technology, will typically reduce a file to 50 percent of its original size.

Disadvantage Images become more pixelated as they are compressed as they save smaller amounts of coloured squares each time

Image CaptureMethod Scanner

How is it used for image capture of graphics

An image scanner is a device that optically scans images, printed text, handwriting, or an object and converts it into a digital image. They can be connected to a computer where the image can be viewed

Method Camera

How is it used for image capture of graphics

Digital Cameras would be used when capturing any 3D image that is unable to be scanned, because of the versatility of digital cameras you can take them almost everywhere and capture images of everything that you are able to. Digital cameras immediately present the image on the camera.

Method Graphics Tablet

How is it used for image capture of graphics

Graphics tablets are a computer input device that enables a user to hand-draw images, animations and graphics. These images are then displayed on the computer monitor although some tablets have a screen.

OptimisingWhy would you optimise? Images are optimised for the web so they can

be easily viewed when they are uploaded to the internet. Images that haven’t been optimised have a bigger file size and take longer to download.

How can you optimise? Reducing image sizes, reducing bit depth, reducing resolution, and compressing images.

Advantage to optimising Viewers can easily see things that are posted to the internet quickly and they are easily accessible.

Disadvantage to optimising One disadvantage of optimising for the web is that they can’t be used for other purposes, such as print, since they have been made smaller due to being compressed