Encoding a black-and-white image as 0s and 1s

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. Our key says 1 = black and 0 = white. How do we write a black pixel?

A 1

B 0

2. A row has 5 pixels: black, white, white, white, black. Which code is right?

A 10001

B 01110

3. A row of 5 white pixels is encoded as...

A 00000

B 11111

4. How many bits does each pixel need in a black-and-white picture?

A Five bits per pixel

B One bit per pixel

5. A 5 by 5 black-and-white picture has 5 rows of 5 pixels. How many bits are needed in total?

A 5 bits

B 25 bits

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
101110		A1 = black, 0 = white
211111		BOne row of a 5 pixel wide picture: white, black, black, black, white
3A key for a black-and-white picture says black is 1 and white is 0		CWhite pixels should be 0, not 1. In the key, 1 means black, so 11111 is a row of black pixels.
4A 5 by 5 picture is written one row at a time, so it takes 5 rows of 5 digits		DThere are only 4 digits but the row has 5 pixels. One digit is missing, so the row should be 10001.
5A row of 5 white pixels is written 11111		E00100 01100 00100 00100 01110
6A row with black, white, white, white, black is written 1001		FA row where all 5 pixels are black

Definitions

1 = black, 0 = white

Fill in the Blanks

Complete each line of code by filling in the missing parts.

Key: 1 = black, 0 = white Row 1 pixels: B W W W B Row 1 code: _____

Key: 1 = black, 0 = white Row 2 pixels: B W B W B Row 2 code: 1 0 _ 0 1

Key: 1 = black, 0 = white Letter T, row 1 is all black: 5 pixels Row 1 code: _____

Grid: 5 by 5, one bit per pixel Bits in the whole grid: __

Key: 1 = black, 0 = white Letter O, row 1 pixels: W B B B W Row 1 code: _____

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A Key: 1 = white, 0 = black

B Row 1: 1 1 1 1 1

C Row 2: 0 0 1 0 0

D Row 3: 0 0 1 0 0

Question 2

A Picture: letter L, 5 by 5

B Row 1: 1 0 0 0 0

C Row 2: 1 0 0 0 0

D Row 3: 1 0 0 0

E Row 4: 1 0 0 0 0

F Row 5: 1 1 1 1 1

Question 3

A Key: 1 = black, 0 = white

B Row 1: 0 1 0 1 2

C Row 2: 0 0 0 0 0

D Row 3: 1 0 0 0 1

E Row 4: 0 1 1 1 0

Question 4

A Black = 1, White = 0

B B W W W B -> 1 0 0 0 1

C W B B B W -> 1 0 0 0 1

D B W W W B -> 1 0 0 0 1

Question 5

A Key: 1 = black, 0 = white

B Row 1: 0 0 1 0 0

C Row 2: 0 1 1 0 0

D Row 3: 0 0 1 0 0 0

E Row 4: 0 0 1 0 0

F Row 5: 0 1 1 1 0

Answer Key

Encoding a black-and-white image as 0s and 1s

Section A: Quick Questions

A — 1

A — 10001

A — 00000

B — One bit per pixel

B — 25 bits

Section B: Match the Pairs

01110 → One row of a 5 pixel wide picture: white, black, black, black, white

11111 → A row where all 5 pixels are black

A key for a black-and-white picture says black is 1 and white is 0 → 1 = black, 0 = white

A 5 by 5 picture is written one row at a time, so it takes 5 rows of 5 digits → 00100 01100 00100 00100 01110

A row of 5 white pixels is written 11111 → White pixels should be 0, not 1. In the key, 1 means black, so 11111 is a row of black pixels.

A row with black, white, white, white, black is written 1001 → There are only 4 digits but the row has 5 pixels. One digit is missing, so the row should be 10001.

Section C: Definitions

1 = black, 0 = white — To encode a black-and-white picture, write 1 for each black pixel and 0 for each white pixel. Work row by row, one bit per pixel.

Section D: Fill in the Blanks

Key: 1 = black, 0 = white
Row 1 pixels: B W W W B
Row 1 code: 10001

Key: 1 = black, 0 = white
Row 2 pixels: B W B W B
Row 2 code: 1 0 1 0 1

Key: 1 = black, 0 = white
Letter T, row 1 is all black: 5 pixels
Row 1 code: 11111

Grid: 5 by 5, one bit per pixel
Bits in the whole grid: 25

Key: 1 = black, 0 = white
Letter O, row 1 pixels: W B B B W
Row 1 code: 01110

Section E: Spot the Error

A — The key is back to front. In this code 1 stands for a black pixel and 0 stands for a white pixel, so it should say: Key: 1 = black, 0 = white.

D — Each row of a 5 by 5 picture needs 5 bits, one for each pixel. This row has only 4 bits. It should be: Row 3: 1 0 0 0 0.

B — A black-and-white picture only uses the bits 0 and 1. The digit 2 is not allowed. The row should be: Row 1: 0 1 0 1 0.

C — The 0s and 1s are swapped. White pixels are 0 and black pixels are 1, so W B B B W must be written 0 1 1 1 0.

D — This row has 6 bits, but the grid is only 5 pixels wide. There must be one bit per pixel, so it should be: Row 3: 0 0 1 0 0.