A pixel's colour in a 24-bit bitmap image is represented using three channels. Colour channel Binary value Denary value Red 11111111 Green 00000000 Blue 000...
Question 1 Report
A pixel's colour in a 24-bit bitmap image is represented using three channels.
| Colour channel | Binary value | Denary value |
|---|---|---|
| Red | 11111111 | |
| Green | 00000000 | |
| Blue | 00000000 |
(a) Complete the denary values in the table. What colour does this pixel represent? [2]
(b) State the binary and denary values for a pixel that appears white. [2]
(c) A pixel has the values Red=0, Green=255, Blue=0. What colour is this pixel? [1]
(d) Explain why 24-bit colour is sufficient for most image display purposes. [1]
(e) Calculate how many different colours can be represented using 24-bit colour depth. [1]
(f) State one disadvantage of using 24-bit colour compared to 8-bit colour. [1]
Answer Details
(a)
| Colour channel | Binary value | Denary value |
|---|---|---|
| Red | 11111111 | 255 |
| Green | 00000000 | 0 |
| Blue | 00000000 | 0 |
Red = 255, Green = 0, Blue = 0. [1] This pixel is pure red, because the red channel is at maximum intensity while both green and blue are at zero. [1]
(b) A white pixel has all three channels at maximum intensity:
- Red = 11111111 (255), Green = 11111111 (255), Blue = 11111111 (255) [2]
White is the combination of all three colour channels at full intensity.
(c) Red = 0, Green = 255, Blue = 0 represents pure green, because only the green channel is at maximum while the other two are off. [1]
(d) 24-bit colour can produce over 16 million distinct colours, which closely matches the number of different colours the human eye can perceive. For most display purposes, this is more than sufficient for a photorealistic image. [1]
(e) The number of different colours representable with 24-bit colour depth:
\( 2^{24} = 16\,777\,216 \) different colours. [1]
(f) 24-bit colour requires three times as much storage per pixel as 8-bit colour (24 bits versus 8 bits), resulting in significantly larger file sizes for the same image resolution. [1]
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