Image Representation
Recap Questions
- How many bits are in extended ASCII?
- What is the difference between ASCII and Unicode?
- What is 00110101 in Denary?
- What is 50 in Binary?
- Which of these units is most appropriate for a music track?
a. GB
b. KB
c. MB
d. B
Learning Objectives
- To be able to calculate the file size of a BITMAP image
- To be able to describe what a pixel is and how they relate to BITMAP images
- To be able to describe colour depth and resolution
Digital Images
- Digital images can be stored in a computer in many different file formats
- Can you name 5 different file formats used to store images?
Answer in your notebook
Image File Types
Bitmap image file formats include:
- BMP
- JPG
- GIF
- PNG
- TIFF
Vector image file formats include:
- SVG
There are also editing formats such as Illustrator (AI) and Photoshop (PS)
Bitmap (or Raster) Images
Bitmap images are made up of PICture ELements or pixels
A pixel is the smallest identifiable area of an image
Each pixel is a single colour and is given a binary value which represents that colour. E.g., 111100000000 might equal red.
A pixel's colour can be changed by changing this value
Image Resolution
Resolution is the concentration of pixels within a specific area
The area is defined by the image width and height in pixels, e.g., 1920x1080
- 72 PPI (Pixels Per Inch) = typical screen resolution
- 300 DPI (Dots Per Inch) = print quality resolution
- Smartphones may have very high resolutions, 300+ PPI
Image Resolution
Resolution is the concentration of pixels within a specific area
The area is defined by the image width and height in pixels, e.g., 1920x1080
- 72 PPI (Pixels Per Inch) = typical screen resolution
- 300 DPI (Dots Per Inch) = print quality resolution
- Smartphones may have very high resolutions, 300+ PPI
Task
For the blank table, you can create your own design and then write out the binary code for it.
File Size of an Image
Height x Width x Colour Depth
Find the height of the image in pixels.
Find the width of the image in pixels.
File Size of an Image
To work out the colour depth, you need to look at how many bits are needed to represent the colours you have available in your image.
2. How many bits do we need to create a unique code for each colour?
1. How many individual colours do we have?
File Size of an Image
Height x Width x Colour Depth
46 x 29 x 3 = File size in bits
How large would this be in bytes?
Task
What would be the file size of this image in:
a. bits
b. bytes
