Image Representation

Question 1

How are bitmap images stored in memory?

Answer 1

• The colour value of each pixel is stored consecutively within VRAM
• Each pixel is MAPPED to one or more addresses
• The video systems read the values from the data buses

Question 2

What are bitmap graphics made of?

Answer 2

• Image is broken down into pixels
• Binary values of pixels determine the colour

Question 3

How to find the resolution of an image? How to find image size?

Answer 3

• Resolution is the number of dots per square inch (dot is pixel)
• Image size = image height x width

Question 4

What is colour depth / bit depth?

Answer 4

• number of colours in image = 2^n
• n is the colour depth
• this is the number of bits required to represent the different colours

Question 5

How do you calculate file size for bitmap images?

Answer 5

• file size = bit depth x image size
• this file size is in bits

Question 6

What is in the header for bitmap files?

Answer 6

• metadata (info about image) : GPS, camera, time and date
• colour depth
• resolution
• THIS INFO IS NEEDED TO DECODE IMAGE

Question 7

What are vector images?

Answer 7

• images are represented as geometric objects
• their properties or attributes such as fill colour, fill style and co-ordinates of corners stored in a list

Question 8

Why are vector graphics used as compared to to bitmapped graphics?

Answer 8

• infinitely scalable without losing quality
• easily manipulated or editable
• small file sizes
• suitable for icons, logos but not photos

Question 9

What are the disadvantages of vector images?

Answer 9

• cannot produce photo-realistic images
• can take longer to render a complex image
• cannot use if colour is likely to vary from pixel to pixel

Question 10

What is a pixel?

Answer 10

the smallest addressable element of an image