File Formats

By Jack Turner

Raster (Bitmap)• Raster or bitmap is a dot matrix data structure, containing columns of dots and rows, of

a graphics image in computer memory. Each dot, has a value which is stored in one or more bits of data (that being if its filled in or not).

• Bitmap images are made by splitting of the screen into tiny scares, these are named pixels• Each colour for each pixel is stored, meaning that images with lots of colours are large in file

size• Low resolution consist of small number of large pixels, where as high resolution have more

pixels which are smaller, giving them higher quality but high resolution means big file sizes. • When Bitmap images are enlarged the pixels increase in size, mean the quality of the image is

then reduce and images then tend to look jagged on the edges.• Commonly used in photographs

Vector • Vectors are graphics that store the instructions for drawing each object on the

page, rather than the picture as a whole • Vector graphics are made up of objects and these objects can be moved, filled,

edited and resized.• These shapes are plotted mathematically, this means that image quality is not

effected when resized.• You can group the objects as one, which makes you able to move and resize them

as one.• You can also layer objects on top of each other• Vector images in general, have smaller file sizes than bitmaps as only the objects

have to be defined. Whereas bitmaps have to define have to define the colour of every pixel on the page.

PNG• PNG, which stands for Portable Network Graphics, is a bitmapped image,

similar to GIF (Graphics Interchange Format) • PNG was created to replace and improve on GIF as a image-file format

that didn’t require a patent license.• Was designed for transferring images on the Internet• Not created for professional-quality print graphics which means that it

doesn’t support non-RGB colour spaces (RGB being a colour model which is additive)

• Most commonly uses file extensions png or PNG are set to MIME (Multipurpose Internet Mail Extensions) media type.

JPEG• JPEG stands for Joint Photographic Experts Group• Computing wise, JPEG is usually used method of Lossy compression (data

coding method that compresses data by losing some of it) for digital photography.

• The amount of compression can be adjusted, the larger the compression the smaller the file size, the lesser the quality of the image (and Vice-versa)

• Has number of image-file formats: the most common for digital cameras and other image capturing devices is JPEG/Exif

• Where as JPEG/JFIF is the most common for transmitting and storing photographic images on the World Wide Web

• Supports around 64k x 64k images sizes.

GIF• GIF which stands for Graphics Interchange Format is a bitmap image format• Compressed using the Lempel-Ziv-Welch (LZW) lossless data compression

technique to reduce the file size without reducing the quality• This compression technique was patented (exclusive rights to a person) • This lead to the creation of PNG. However, all the relevant patents have now

expired • Used widely across the World Wide Web due to its wide portability and support.• Supports 8 bits per pixel meaning a single image can have up to 256 distinct

colours.• Colours chosen from the 24-bit RGB colour space.• GIF supports animations and is suited for simple graphics and logos with a solid

areas of colour.

RAW• Camera raw image file contains minimally processed data from the image sensor of

a digital cameras, motion picture film scanner or image scanner• Loads of pixels and you can zoom really far in and still have good quality, but the

files in this state take up a lot of room.• Not directly usable as an image but has all of the information needed to create an

image.• Have not been processed yet, which means they are not ready to be printed or

edited with a bitmap graphics editor.• Raw images need to be converted to be able to edit them or print them so raw

files are converted to a file format such as JPEG or TIFF (Tagged Image File Format).• This is done by a raw converter where it is made into a positive file format which

makes them “positive” file formats like JPEG or TIFF.

Resources

• http://www.webopedia.com• http://www.howstuffworks.com• http://www.fileinfo.com/