1.
What are Pixel Dimensions?
 
 Pixel Dimensions are the number of distinct pixels in a digital televison or computer monitor. It is usually width x height


What is a DPI resolution (Dots Per Image)? 

DPI Resolution is used to measure the resolution (how many pixels a monitor can display or how fine a printer can print) of an image both on screen and in print. DPI is not dots per square inch.

What does Quality of an image mean?

Image quality means the condition of the image.

Compression Settings
 It means when you change the size of an image, for example when you email a image to someone and you want to change the size.

2. Bitmap/Raster  
Most images you see on your computer are made of bitmaps(also known as rasters). A bitmap is a map of dots, or bits, that looks like a picture as long you are sitting a reasonable distance away from the screen.

Vector
 Vector graphics are created in graphics packages and consist of shapes called objects. Even if an object in a vector graphic is quite large, it doesn't need a lot of computer memory. Therefore the file size of a vector graphic is often very small.

What is the difference between bitmap and vector graphics?
Bitmaps are made of pixels of different colours, vectors are made up of objects. The file size of bitmaps have to be large, as the computer stores details of every pixel and vectors have to be small, as the computer stores details of objects, which do not require much memory. Bitmaps look more realistic and vectors dont look realistic (many of them look like cartoon images). When bitmaps are resized they loose quality and when vectors are resized they do not loose quality.