GCSE COMPUTER SCIENCE Data 2.2 Characters and Images

ASCII Computers have to be able to represent letters and symbols as well as numbers. Simply, the idea is to give each character a number, as a code and store the codes and their meanings in a table. A common code is ASCII - the American Standard Code for Information Interchange. Symbol Binary A 100 0001 B 100 0010 C 100 0011 D 100 0100 E 100 0101 F 100 0110 This uses seven bits to store characters. Seven bits is enough to code 128 different characters. ACTIVITY Using this information write a definition of ASCII in your exercise books. You do need to know what it stands for and how many bits it uses.

Use the table of ASCII binary codes to decode these letters Activity 1 Use the table of ASCII binary codes to decode these letters ASCII Binary Code Decimal Value Character 110 1000 104 h 110 0101 110 1100 110 1100 110 1111

Use the table of ASCII binary codes to decode this: Activity 2 Use the table of ASCII binary codes to decode this: Character Decimal Value ASCII Binary Code H o l a n d Character Decimal Value ASCII Binary Code P a r k

Activity 3 Copy and complete the questions below. Question Answer What is the ASCII code for a blank space? 32 - 00100000 Why is it important to have a code for a blank space? Otherwise the computer would not recognise where one word finishes and the next begins. Write your name in ASCII. Write a word of your choice in binary in your book. Swap with the person next to you and see if you can decode each others word.

Write this definition of Unicode in your exercise books. Unicode is an alternative character set and encoding system. It uses 16 bits to encode each character and is therefore able to represent far more characters than ASCII (over 65,000). ACTIVITY Write this definition of Unicode in your exercise books.

Write this definition of a Bitmap Image in your exercise book. Bitmap Images Images can be represented using a grid of squares called pixels. Each pixel can be uniquely identified by its position in the grid (x/y coordinates) and each pixel is a single colour. ACTIVITY Write this definition of a Bitmap Image in your exercise book. Interactive Activity http://learncomputing.org/bitmap.php

Write this definition of Colour Depth in your exercise book. A binary code is used to represent the colour of a pixel. The number of bits used to store each pixel’s colour is known as the colour depth. The greater the colour depth, the more colours can be represented. ACTIVITY Write this definition of Colour Depth in your exercise book. The number of colours that can be represented can be calculated using 2depth. For example a colour depth of 1 bit can represent 2 colours. 2no. of bits Therefore 3 bits = 23

Copy and complete the colour depth table below. Activity 4 Copy and complete the colour depth table below. Colour depth Number of colours Range 1 bit (think 21) 2 0 – 1 2 bit (think 22) 3 bits (think 23) 8 0-7 4 bits 16 8 bits 16 bits 24 bits 32 bits

1-Bit Images This image has only two colours, black and white and therefore has a colour depth of 1 bit. 1, 0, 0, 0, 1 1 = white 0 = black 1, 1, 1, 1, 0 1, 0, 0, 0, 0 0, 1, 1, 1, 0 0, 1, 1, 1, 0 1, 0, 0, 0, 0

Activity 5 Copy and complete the grid below to reveal what character this code produces. Binary code 00000 01111 11110 1 = white 0 = black Use a ruler.

Produce the binary code to produce the letter ‘G’ in the grid below. Activity 6 Produce the binary code to produce the letter ‘G’ in the grid below. Binary code 1 = white 0 = black Use a ruler.

The first number always represents white. How could his be stored more efficiently? This image has only two colours, black and white. 1, 3, 1 The first number always represents white. 4, 1 1, 4 0, 1, 3, 1 0, 1, 3, 1 1, 4 ACTIVITY Complete the Image Representation worksheet using this method.

(height x resolution) x (width x resolution) x colour depth Resolution and File Size RESOLUTION The resolution or pixel density of an image is the number of pixels per inch (PPI). Generally speaking the higher the resolution the higher the quality of the image. FILE SIZE You can calculate the amount of storage space required to save an image using a formula. FORMULA (height x resolution) x (width x resolution) x colour depth 8 Calculate the file size of an image with - dimensions of 2 inches x 3 inches - resolution (also called pixel density) of 200 PPI - colour depth of 4 bits. METHOD (2 * 200) * (3*200) * 4 / 8 ACTIVITY ANSWER 120,000 bytes

Activity 7 Calculate the file size of an image with dimensions of 3 inches x 4 inches, a pixel density (also known as resolution) of 300 pixels per inch and a colour depth of 8 bits. Give your answer in bytes. METHOD (3 * 300) * (4*300) * 8 / 8 ANSWER 1,080,000 bytes Hint: File size formula is (height x resolution) x (depth x resolution) x colour depth / 8

Activity 8 Calculate the file size of an image with dimensions of 5 inches x 7 inches, a pixel density of 400 pixels per inch and a colour depth of 3 bits. Give your answer in bytes. METHOD (5 * 400) * (7*400) * 3 / 8 ANSWER 2,100,000 bytes Hint: File size formula is (height x resolution) x (depth x resolution) x colour depth / 8

Print out one copy (include your name) and stick it in your book. Activity 9 Revision Poster CREATE An A4 revision poster summarising the information you have learnt in the Characters & Images topic. TITLE 2.2 Characters & Images TOPICS ASCII, ASCII Examples, Unicode, Colour Depth, Bitmap Images, Resolution and File Size. FINISHED Print out one copy (include your name) and stick it in your book.

Activity 10 Crossword Create a crossword based on this topic using the online crossword generator linked below. It should have a minimum of 10 questions. When you have finished, paste your crossword on to a Powerpoint slide and name it 2.2 Characters and Images. Print out one copy (include your name) and stick it in your book. http://puzzlemaker.discoveryeducation.com/CrissCrossSetupForm.asp puzzle maker criss-cross