Quiz: Image Representation (Colour by Numbers)

Multiple-Choice Questions

1. What are computer screens divided up into?
A) Lines
B) A grid of small dots called pixels
C) Squares of paper
D) Numbers only

2. In a black and white picture, what can each pixel be?
A) Red or blue
B) Large or small
C) Black or white
D) Round or square

3. In the number code, what does the very first number in a line always represent?
A) The number of black pixels
B) The number of white pixels
C) The total number of pixels
D) The colour of the picture

4. If the first pixel in a line is black, how does the code for that line begin?
A) With the number 1
B) With the number 9
C) With a zero
D) With a blank space

5. What name is given to the method used in this activity to compress images?
A) Binary coding
B) Run-length coding
C) Pixel mapping
D) Modem coding

6. What does a fax machine do?
A) Prints coloured photographs only
B) Scans a black and white page into pixels and sends them to another fax machine
C) Stores pictures without using numbers
D) Draws pictures using tracing paper

7. In the "Extra for Experts" colour version, what does the second number in a pair represent?
A) The length of the run
B) The position of the pixel
C) The colour
D) The size of the grid

8. About how much are fax images generally compressed to, according to the resource?
A) A half of their original size
B) A seventh of their original size
C) A hundredth of their original size
D) They are not compressed at all

Short-Answer Questions

9. Explain, in your own words, why computers need to compress images (use the fax example to help your answer).

10. The discussion point asks: if you could only use numbers up to seven, how would you represent a run of twelve black pixels? Describe the method suggested in the resource.

11. Name two situations mentioned in the resource where computers need to store pictures.

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Answer Key

1. B) A grid of small dots called pixels
2. C) Black or white
3. B) The number of white pixels
4. C) With a zero
5. B) Run-length coding
6. B) Scans a black and white page into pixels and sends them to another fax machine
7. C) The colour
8. B) A seventh of their original size

1. Compression is needed to save storage space and reduce transmission time. Without compression, images (like faxes) would take much longer to send and require much more storage space—the resource notes fax images without compression would take seven times as long to transmit.

1. Code a run of seven black pixels, followed by a run of zero white pixels, then a run of five black pixels (7 + 5 = 12 black pixels total, using only numbers up to seven).

1. Any two of: a drawing program, a game with graphics, or a multi-media system.