Writing an RGB colour in binary

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Quick Questions

Shade in the A or B circle for each question.

1. How is the RGB colour (255, 128, 0) written in binary?

A 11111111 10000000 00000000

B 11111111 1000000 0

2. How many bits are used for each colour channel (red, green or blue) in 24-bit colour?

A 8 bits (one byte)

B 24 bits

3. Which binary byte stores the red value 255?

A 10000000

B 11111111

4. The green value is 0. How is it stored in its byte?

A 0

B 00000000

5. How many bytes are joined together to make one pixel's colour in 24-bit RGB?

A 3 bytes

B 1 byte

Match the Pairs

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

Left column		Right column
111111111 10000000 00000000		AThe bytes are in the wrong order. 11111111 is in the red position, but the 255 belongs to green, so this is pure red.
200000000 00000000 11111111		BThe RGB colour (255, 128, 0) written as three 8-bit bytes: red, green and blue joined to make one pixel
3Each colour channel (red, green or blue) uses one byte, which is 8 bits		C255 = 11111111
4Join the three bytes for red, green and blue in order to make one pixel		D(255, 0, 128) = 11111111 00000000 10000000
5(255, 128, 0) = 11111111 1000000 0		EThe bytes are not each 8 bits. The 128 is only 7 bits (1000000) and the 0 has been left as a single digit.
6(0, 255, 0) = 11111111 00000000 00000000		FThe RGB colour (0, 0, 255), which is pure blue, written in binary

Definitions

11111111 10000000 00000000

Fill in the Blanks

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

Red 255 = 11111111 Green 128 = 10000000 Blue 0 = ________

Each colour channel uses _ bits (one byte).

Red + green + blue = _ bytes per pixel.

(255, 128, 0) = 11111111 ________ 00000000

(255, 0, 0) -> ________ 00000000 00000000

Spot the Error

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

Question 1

A # One byte = 4 bits per channel

B red = 255 -> 11111111

C green = 128 -> 10000000

D blue = 0 -> 00000000

Question 2

A colour = (255, 128, 0)

B red = 255 -> 11111110

C green = 128 -> 10000000

D blue = 0 -> 00000000

Question 3

A colour = (0, 255, 0)

B red = 0 -> 0000

C green = 255 -> 11111111

D blue = 0 -> 00000000

Question 4

A colour = (64, 0, 255)

B red = 64 -> 10000000

C green = 0 -> 00000000

D blue = 255 -> 11111111

Question 5

A colour = (255, 192, 0)

B red = 255 -> 11111111

C green = 192 -> 01100000

D blue = 0 -> 00000000

Answer Key

Writing an RGB colour in binary

Section A: Quick Questions

A — 11111111 10000000 00000000

A — 8 bits (one byte)

B — 11111111

B — 00000000

A — 3 bytes

Section B: Match the Pairs

11111111 10000000 00000000 → The RGB colour (255, 128, 0) written as three 8-bit bytes: red, green and blue joined to make one pixel

00000000 00000000 11111111 → The RGB colour (0, 0, 255), which is pure blue, written in binary

Each colour channel (red, green or blue) uses one byte, which is 8 bits → 255 = 11111111

Join the three bytes for red, green and blue in order to make one pixel → (255, 0, 128) = 11111111 00000000 10000000

(255, 128, 0) = 11111111 1000000 0 → The bytes are not each 8 bits. The 128 is only 7 bits (1000000) and the 0 has been left as a single digit.

(0, 255, 0) = 11111111 00000000 00000000 → The bytes are in the wrong order. 11111111 is in the red position, but the 255 belongs to green, so this is pure red.

Section C: Definitions

11111111 10000000 00000000 — The RGB colour (255, 128, 0) written in binary. Each number becomes its own 8-bit byte for red, green and blue, and the three bytes are joined together to make one pixel.

Section D: Fill in the Blanks

Red 255 = 11111111
Green 128 = 10000000
Blue 0 = 00000000

Each colour channel uses 8 bits (one byte).

Red + green + blue = 3 bytes per pixel.

(255, 128, 0) = 11111111 10000000 00000000

(255, 0, 0) -> 11111111 00000000 00000000

Section E: Spot the Error

A — Each RGB channel is stored in one byte, and a byte is 8 bits, not 4. The comment should say 'One byte = 8 bits per channel'.

B — 255 in binary is 11111111 (all eight bits on). 11111110 is 254. The line should be red = 255 -> 11111111.

B — Every colour channel must be a full 8-bit byte, so 0 needs leading zeros: 00000000. Only 4 bits would break the 24-bit pixel.

B — 10000000 is 128, not 64. The 64 place value is the second bit from the left, so 64 is 01000000.

C — 192 = 128 + 64, so the two left-most bits are on: 11000000. 01100000 is 96.