Each pixel’s colour could be defined by sorting its assosiated index number instead of the longer RGB value. This look-up table was more efficient in handling images with up to 256 colours because each pixel can be stored in 8-bits instead of 24. Microsoft was successful in futher optimising the BMP format by tying it even more closely to Windows’ API, adding features like control over which occurs to change when images are viewed on limited colour screens.

BMP – Bitmap

TIFF - Tag Image File format

GIF – graphics interchange format

JPG – Joint Picture Experts Group

Each of these is a suffixes. They’re the four main bitmap standards and are usually found at the end of a saved file’s name, e.g mastodon logo.jpg. They are used to enable reliable exchange of graphical information between different applications and different media.

What is a bitmap? It’s an array of pixel values. At its most basic, e.g a black and white bitmap of a circle is just a grid of squares where each one is either black or white. The simplest file format used to describe this needs a file header and fixed fields saying what the width and height are for the grid are and underneath the image data can be stored as a stream of single bits with 0 representing white and 1 for black.
For the BMP, with black and white printer and monitors, that was all that was needed of bitmap formats like Microsoft Paint’s MSP, but when colour monitors came around it all changed. Screens were now able to show 16 to 256 colours, the simple on/off bitmap wasn’t enough. The solution? Increase the bit-depth. Instead of storing one pixel value per bit, you could easily store more bits per pixel. With 2 bits you could define 4 colours, with 3 bits you could define 8 colours and at 8 bits you would have reached 256 colours. Other bitmap standards emerged to support new display-based demands like PCX, but the most important one today is Microsoft’s BMP, Windows’ original bitmap format.
Each pixel’s colour could be defined by sorting its assosiated index number instead of the longer RGB value. This look-up table was more efficient in handling images with up to 256 colours because each pixel can be stored in 8-bits instead of 24. Microsoft was successful in futher optimising the BMP format by tying it even more closely to Windows’ API, adding features like control over which coours to change when images are viewed on limited colour screens.

TIFF is different because of its tag-based structure, BMP is built on a fixed header with fixed fields followed by sequential data, TIFF has a more flexible structure. It can handle multiple images and data in a single file through the inclusion of tags in the file header. At the start of each TIFF is an 8-byte header that points to the position of the first IFD tag (tags show the basic geometry of the image, such as it size or define how the image data is arranged and whether various image compression option are used). This IFD can be of any length and contain any number of other tags enabling completely customised headers to be produced. The IDF also acts as a map to where image data is stored in the file, because the files aren’t stored in order.
The TIFF’s tagged nature has many benefits. On a structural level, the fact that many files can be conatined in the one file is useful when it comes to storing alpha channels (a special type of channel used in graphics software for saving selections). The data isn’t stored scan line by scan line, but is broken up into tagged strips of multiple scan lines. It’s crucial for handling the large files necessary for print work as it allows for easy buffering and random access. In particular it means that, to load just the bottom of an image, the whole file doesn’t have to be read and held in memory. Other tags are used for defining features like colour mode of the file and teh choice of compression method.
TIFF’s strength is its print-oriented flexibility through features like tiling, multiple colour spaces and LZW (Lempel-Ziv-Welch) compression. At first, like BMP, TIFF only offered a variation on RLE (Run-length Encoding) compression called PackBits which is only efficient for indexed images.

GIF (pronounced ‘jiff’ or ‘giff’), was created by Compuserve ( short for CompuServe Information Service, it was one of the first and largest online services) and is is a bit-mapped graphics file format used by the World wide web (WWW). GIF uses teh 2D raster dat type and is encoded in binary. There are two versions of the format 87a(this one allows for the possibility ofn animated GIF) and GIF89(this one can be specified for interlaced GIF presentation). GIF supports colour and many other resolutions. It also includes data compression, its limited to 256 colours. It’s more effective for scanned images such as illustrations rather than photos. The images are compressed using LZW compression, reducing the file size by 30-50% or more.
Unlike JPG, GIF is a lossless compression technique, which means it doesnt take pieces off the image to make the file smaller. It’s better than JPG for images with a few distinct colours, like black and white images and small text only a few pixels high, because JPG distorts the edges where there is sharp contrast in colour. With an animation editor, GIF can be put together to make animated images. In GIF supports transparency, where the background colour can be set to transparent in order to let the colour on then underlying web page to show through.
There are interlaced GIFs that load, allowing the user to see parts of the image while it loading. Interlaced files take long to decompress, and may take longer to download. It isnt worth the decompression time for small files.

JPG is one of the image files supported by the net. As mentioned before, JPG is a ‘lossy’ compression technique thats is designed to compress colour and grayscale continuous-tone images. It’s called ‘lossy’ because when it compresses a image, it takes pieces out of the file, trying to make it smaller and easier to compress. This degrades the quality of the image, but the difference is only slight so the human eye doesnt notice. Sometimes this is a good thing, like on website which require the image to uploaded or when the image needs to be sent in an email, it makes the process faster. JPG support up to 16 million colours (RGB – 24 bits and grayscale – 8 bits), which doesnt limit colours and it’s best used to store photos and complex graphics. It doesnt work well with line drawings, lettering or simple graphics because there isnt much of the image to lose in the compression process, so the image loses its sharpness and is distorted.
JPGs use high compression for really small files and a little compression for larger files.
There a progressive JPGs, which are the equivalent to interlaced GIFs. They’re images created using the JPG compression algorithms that will ‘fade in’ lines until the entire image has complete arrived. Like the interlaced GIF, a progressive JPG is a more appealing way of delivering an image at modem connection speeds. User with faster connections are not likely to notice the difference.

There are two types of computer graphics; vector and raster. Vector graphics (aka geometric modelling or object oriented graphics) is the use of geometric primitives such as points, lines, curves and polygons.Vector images define curves and lines by mathematical formulas, enabling you to scale the image larger or smaller without taking a hit on the image quality. Adobe Illustrator and Macromedia Freehand are applications that can enable you to create vector images. Vector-based images are best when working with small type and bold graphics (requiring crisp curves and lines) no matter what size they’re scaled to.Vector graphics (aka geometric modelling or object oriented graphics) is the use of geometric primitives such as points, lines, curves and polygons. Vector based images do have several advantages and are resolution dependent. A raster image is a data structure representing a generally rectangular grid of pixels, or points of colour, viewable on a computer monitor, paper or other display medium. They’re commonly stored in image files with varying formats. Raster images are made up entirely of pixels. It’s not quite as easy to scale the images, but with some care, you can obtain excellent results. Adobe Photoshop is probably the best example of an application for editing raster images. Raster-based images are best when working with continuous tone images, like photographs. The picture of the eagle is a raster image, and if you zoom in on the top of its beak, you can see it’s made up thousands of pixels. Having enough pixels to make an image is essential. An image needs to have at least 300 dpi (dots per inch), in order to be colour separated and produced with clarity. An image that isn’t the require resolution will appear chunky as if it were already being viewed up close.Putting a raster image in an illustration program and then writing an EPS file won’t convert it to a vector image. As far as colour separation is concerned, it does nothing. Raster images are best suited for ‘4-colour-process’ which is the process used for subliminal, near-photographic decals and can be used for t-shirt images.