Digital Images

Digital Images

1. Bitmaps

   • Bitmaps are images made up of pixels (short for Picture Elements) which are small squares of colour.
   • Bitmaps are created by arranging pixels on the "canvas", which is the term for the area which defines the image.
   • The bitmap's information header contains details of the height and width of the image and the colour depth (number of bits used to represent colour) for each pixel.
     • This metadata is essential as without it the computer will unable to properly place or display the pixels as it will be unable to interpret the data given to it.
   • In binary form, the bitmap consists of a string of binary digits. The computer distinguishes pixels from one another by the colour depth of the image (x amount of bits represent one pixel) and is able to arrange these pixels as it is aware of the dimensions of the image.
   • The height and width of an image are the number of pixels along the y-axis and the number of pixels along the x-axis respectively.
   • Colour depth is the number of bits used per pixel to represent the pixel's colour. This can range from one (black and white) to 48 bits per pixel.
     • When using a colour depth of 8 bits or less indexed colour palettes will usually be used to determine pixel colour. These consist of tables of preset colours which are referenced by the computer when it displays the image.
     • At higher colour depths the colour of a pixel is determined by the ratios of red, blue and green used. A set amount of bits are devoted to each colour depending on the colour depth.

2. Vector Images

   • Vector images are made up of mathematically-defined geometrical objects.
   • Objects can range from individual lines to circles.
   • Objects are defined by mathematical formulae and parameters and their properties.
     • Formulae determine the shape of the object. The parameters for formulae vary depending on the object drawn. For example, circular objects will be defined by the co-ordinates of their centre and the length of their radius.
     • Properties define the appearance of the object in its defined structure. Properties include factors such as line thickness and colour.
     • The formulaic nature of vectors allows them to be redrawn to any scale without image distortion.