1. Representation of Data in Computer Systems
Images

2. Activity 1 5 minutes to complete the starter sheet. Today’s keywords
pixels
metadata
Colour depth
Image resolution
Lossy compression
Dots Per Inch (DPI)
Black = 1
White = 0

3. Introduction Representing Images
Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Representing Images
As we already know, computers can only deal with 0s and 1s (binary).
Whenever a computer represents anything (numbers, characters etc) it has to do so in binary.
It is exactly the same with images.
Images are represented in binary…

4. How are images stored? Bitmaps
Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Bitmaps
Bitmap images are made up of rows of “dots” called “pixels” (picture elements).
Each pixel is represented by a binary number.
Behind the scenes, this 1 bit image (with each colour represented by a bit) is in fact a series of numbers.

8. Effects of Resolution on the Quality and File Size of an Image
Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Dots Per Inch (DPI) / Resolution How can we improve the quality of the image in terms of ‘how defined’ the image is? The answer is that we pack more pixels into the same space. HD movies and images give the illusion of higher quality pictures because the pixels are smaller giving more detail and making the image less ‘blocky’ or ‘pixelated’.
Higher DPI means higher resolution which in turn means a more defined image!
…but also more data and therefore a bigger file size!

9. Effects of Resolution on the Quality and File Size of an Image
Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Dots Per Inch (DPI) / Resolution
Higher DPI means higher resolution which in turn means a more defined image!
…but also more data and therefore a bigger file size!

10. …but also more data and therefore a bigger file size!
Effects of Resolution on the Quality and File Size of an Image
Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Dots Per Inch (DPI) / Resolution
Higher DPI means higher resolution which in turn means a more defined image!
…but also more data and therefore a bigger file size!

11. …but also more data and therefore a bigger file size!
Effects of Resolution on the Quality and File Size of an Image
Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Dots Per Inch (DPI) / Resolution
Higher DPI means higher resolution which in turn means a more defined image!
…but also more data and therefore a bigger file size!

12. …but also more data is needed therefore increasing the file size!
Effects of Colour Depth on the Quality & File Size of an Image
Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Colour Depth How can we improve the quality of the image in terms of ‘its depth in colour’? The answer is that we have more colours to choose from for each pixel. The greater range of colours makes the image look more ‘real’.
Higher number of colours that a pixel could be means higher colour depth which in turn means a more real looking image!
…but also more data is needed therefore increasing the file size!

13. Effects of Colour Depth on the Quality & File Size of an Image
The greater the number of colours in the image the better the quality but the more storage space is taken to save the image and the more memory (RAM) is needed to display the image.
1 bit
2 possible colours
Black or white (monochrome) 1
4 bit
16 possible colours (0-15)
…in one pixel 8 4 2 1

14. Effects of Colour Depth on the Quality & File Size of an Image
8 bit colour depth (High Colour)
256 possible colours (0-255)
24 bit (True Colour)
16,777,216 possible colours!

15. 24 bit colour depth (True Colour)
8 bits
8 bits
8 bits
= 24 bits
256 x 256 x 256 =
16,777,216 possible colours!

16. How are images stored? Summary
Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Summary
Bitmap images are made up of rows of “dots” called “pixels” (picture elements)
The greater the number of “dots per inch” (pixels), the higher the quality but also the larger the file size as it holds more pixels / data.
Also, the more colours, the more real the image looks but the bigger the file size as each pixel is generated from a larger binary number, therefore more data.

17. Metadata Metadata Learning Objectives:
(a) Explain the representation of an image as a series of pixels represented in binary.
(b) Explain the need for metadata to be included in the file such as height, width and colour depth.
(c) Discuss the effect of colour depth and resolution on the size of the image file.
Metadata
Because images are stored as binary numbers, the computer needs to be told how to interpret the numbers to produce the image.
It needs to be told the height and width or the image (in pixels) and the colour depth. Once known it can work its way through the binary numbers, interpreting them correctly and produce the intended image on the screen.
This is basically “data about data” and it is known as METADATA. With metadata the computer user (you!) can make sense of all the binary data.

18. Recap: what factors affect image quality & file size?