Topic 16-Digital Imaging

Two types of graphic:

• Bitmap
• Vector

Bitmap: photograph

• Image itself is stored as a map showing the position of each pixel
• Details of the colour of each pixel are stored
• This is a huge amount of data

In general:

• Bitmap are big files so they take lots of space on a disk. They also take a long time to upload (i.e.put onto a website) or download (i.e. to appear on a user's screen)
• They can lose their sharpness when they are enlarges or reduced in size

Vector: drawing

• Information about how to draw the image is stored rather than the image itself
• Stored as a series of wquations
• The equations tell the computer how to draw the parts of the image
• Only instruction/equations are stores, so file size is small

In general:

• Are used for more precise images such as: maps, technical, drawing/plans or images that contain a limited number of colours
• Are not good for re-creating photgraphic type artwork
• Are uploaded and downloaded faster owing to their smaller file size
• Can be enlarged or reduced, keeping their sharpness
• Do not take up much space when stored compares to bitmap images 
• Are made up of objects that can be edited and filled with colour

Impact of large file size for bitmap:

• Large file size means large upload time (i.e. time to transfer file to a website is large)

• Large file size means download time is large (i.e. the time taken for a user to view the image on a website)
• Files are compressed to reduce file size

Impact of small file size for vector graphics:

• Quick upload time
• Quick download time
• Can store lots more images in the same storage space compared to bitmap

Advantages of vecotr graphics compared to bitmap graphics:

• Vector graphics have very small sizes. Small file size means that a viewr or the graphics does not wait long to see it appear on the screen
• They have a low upload and download time and so are ideal for the Web 
• They are much easier to edit and can be resized without any loss in quality
• By using software it is easy to zoom in and out a vector image

Disadvantages of vector graphics:

• Only suitable for images with a limited number of colours
• No good for images with continuous colours like a photograph

Tootls and techniques used for manipulating still images:

• Graphics can be manipulated in a number of ways including:
• Zoom: allows a user to magnify or reduce the size of an image on a screen
• Selections: allows the whole or part of an image to be selected for editing
• Transformationing: using rotation or reflection
• Sizing: the graphic is pre stored at a certain size but can have its size altered
• Scaling: is sizeing to a pre determied size often expresseed as a percentage
• Copying: a single image can be copied many times
• Moving: an image can be moved to any place where it is suitable
• Layering: add elements to an image that exists serparately

Colour effects:

• There are many imaging effects that can be used on a pictiure:

• Colour palette
• Gradient tool

Image effect:

• There are many imaging effects that can used on a picture
• Touch up
• Red eye reduction 
• Smoothing

Common File Formats:

• GIF file- graphical interchange format. Original image is compressed. They have the advantages that they are small in file size. A max of 256 colours can be used, this means don't quite look like the original image. They are good for images and photographs on the web
• JPEG- Joint Photographic Expert Group. Ideal for photos. Original image is compressed. Uses 16 million colours

GIF file format:

• Uses 8 bits for colours
• Maximum of 256 colours 
• Transparency
• Uses compression 
• Used for simple graphics

JPEG files format:

• Uses 24 bits for colour
• Maximum of 16.7 million colours
• Uses compression
• Used images with continuous colour (e.g. photos)
• Transparency 

Other common file formats:

• PNG- Portable network Graphics
• TIFF- Tagged Image File Format
• PSD- PhotoShop Document
• BMP-BitMaP