Pixel: (also known as Picture element)

A pixel is the smallest thing on a monitor, they are little dots of information that make a picture.Each pixel will have information on what shade of RGB colours it will have to determin how a picture looks.

When it comes to image resolution pixels are used is huge amounts, such as a screen resolution of 1024 x 768 will have 1024 x 768 pixels.The higer the resolution the more pixels it will have and also a difference in size per pixel.When the resolution of something gets bigger the sharpness and the quality increases.

The intensity of pixels in an image is variable in colour systems, each pixel has typically three or four dimensions such as red, green, blue or cyan, magneta, yellow and black.

Different resolutions, on left 640 x 480

on right 800 x 600 

Raster images A raster image is normally defined as a rectangular group of pixels, each pixel has one or more numbers that define how the colour of the pixel should be displayed.

The most simple representation of a image is that each pixel is three 8-bit colour values ranging from 0-255 that define the amount of red, green and blue in each pixel.In the right proportions red, green and blue can be combined to form 16,777,216 different shades of colour. When it comes to compression there are two different types, lossy and lossless. Lossy is when an image is compressed but some of the image quality is lost when doing so.Lossless is when an image is compressed but none of the quality is lost in the process.

Bitmap images (may be called Rasta images), bitmap images are made from pixels .If bitmap images are rescaled then the image can become jagged or blocky .Each pixel in a bitmap image has its own assigned colour and value. Bitmaps are used for artwork created in painting programs and continuous-tone images such as photographs.

(This is a blocky picture i made in photoshop to shop what happens to bitmap images when stretched out.)

http://www.webopedia.com/TERM/B/bit_map.html  << (info on bitmap can be found here)

Vector images and Raster images

An advantage of using a vector image over a raster image is that vector images are not restricted to a rectangular shape like bitmaps.Vector images can be placed over an object and the object below will show through unlike bitmap. The main disadvantage with vectors is that they’re unsuitable for making photo imagery.

Gif (graphics interchange format)

One of the most common used formats on the web, this is because of the small amount of space they take up.Gifs use a certain type of compression called lossless, wich means the file size gets smaller without damaging the picture.Gifs also have transparancy wich means they can sit on top of the back ground image without having the big rectangles around the image.Gif images use a palette of up to 256 distinct colors from the 24-bit RGB color space.Gif images are a series of images put together in order to make a moving image.

http://i227.photobucket.com/albums/dd287/stackoidz/safeee.gif

PNG (Portable Network Graphics)

PNG is a bitmapped image that uses lossless compression, it can use 48-bit colour, alpha channels, built in gamma and colour correction, tight compression and the ability to display at one resolution and print at another.PNG was made to to replace GIF because of the licence that came with GIF, PNG had no license.

Tiff (Tagged image file format):

Tiff is a container format thats is used to store images such as photographs and line art.Tiff is used alot with black and whites images and is widely supported by image manipulation programs.Tiff is a very flexible file format, it can handle multiple images and data in a single file through the inclusion of tags.Tiff also uses lossless file compression.

JPEG (joint photographic experts group)

A jpeg is a compressed image that is used mostly for the internet, for its small file size. Jpegs use lossy compression which means that some of the picture quality is lost in the process. The joint photographic experts group founded jpeg in 1986.There is an interlaced progressive jpeg format in which data is compressed into muliple passes of progressively higher detail, this is used for large images over the internet downloading on slower connection.

A jpeg that has used the lossy compression mutiple times.

PSD ( Photoshop document)

Psd is a photoshop document,it is the main type of file used in photoshop.One of the good things about this type of document is that it uses layers, these layers can be stack upon each other to create the desired result.When the psd’s format is converted into a jpeg, tiff, gif, or pther graphic format, the layering is flattened into one bitmapped image.

All the different layers used in photoshop.

Vector images Vector images are made of lots of individual scalable objects, these objects are made of mathematical equations than pixels so they are always at the highest quality. These objects consist of curves, lines and shapes that have editable attributes such as outline, fill and colour. Changing the attributes of a vector does not effect the object itself, you can can the attributes as much as you want without destroying the object itself. 

This is a vector image.