Topic 16- Digital imaging

There are two types of graphic, bitmap is the first. 

Bit map images are made up of millions of pixels, normally very small. This means you cannot actually see them in the image until it is zoomed in (the more pixels the larger the file size). The image itself is stored as a map showing the position of each pixel and the details of the colour of each pixel are stored, meaning there is a huge amount of data and files to store bitmap images are large. This means there are large upload times, download times and files are compressed to reduce file size. Bitmaps are harder to edit than a vector and the images lose sharpness when resized. 

The second type of graphic is a vector. 

Vector graphics are graphics that use maths to work out the positions and lengths of lines and curves, etc. The information about how to draw the image is stored rather than the image itself, it is stored as a series of equations. The equations tell the computer how to draw the parts of the image. Only instructions or equations are sored so the file size is small. 

This means there is a quick upload and download time and more images can be stored in the same storage space compared to bitmaps. However, vector graphics are only suitable for images with a limited number of colours and is no good for images with continous colours, like photographs. 

Graphics can be manipulated in a number of ways including:

• Zoom
• Selection
• Transformation- rotate, reflect
• Sizing
• Scaling
• Copying
• Moving
• Cloning 
• Brush settings
• Layering

Many colours effects can be applied to a graphic using a colour palette or gradient tool.

GIF files

Graphical Interchange Format is where the original image is compressed. They have the advantage that they are small in file size, however a maximum of 256 colours can be used so they don't look like the original image. They are good for images and photographs on the web. 

GIF files use 8 bits for colour, compression, is used for simple graphics and transparency. 

JPEG 

Joint Photographic Expert Group are ideal for photos, the original image is compressed and uses 16.7 million colours. 

JPEG files use 24 bits for colour, compression, is used for images with continous colour (e.g. photos) and transparency. 

Other common file formats are PNG (Portable Network Graphics), TIFF (Tagged Image File Format), PSD (PhotoShop Document) and BMP (BitMaP) 

Optimisation is the reduction of the file size of the image. 

It is important to remember that visitors to your site will not want to wait very long for pages to load. This means you should, for everything that you can, streamline your content and that includes the size of the images you use.