Pixels, bitmaps and colour depth

Overview

Pixels, image size and colour depth, how many colours a given depth can show, how more pixels or bits change an image, and decoding short rows of bitmap data.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a pixel?

   Model answer

   A pixel is a single point in an image, and the word is short for picture element. Each pixel shows one colour.

2. 2

   How do pixels make up a bitmap image?

   Model answer

   A bitmap image is a grid of pixels arranged in rows and columns. The colour of each pixel is stored as a binary code.

3. 3

   How is the size of a bitmap image described?

   Model answer

   Image size is given in pixels as width × height. An image 800 pixels wide and 600 pixels high is 800 × 600.

4. 4

   How many pixels are in an image of 1,024 × 768?

   Model answer

   The image contains 786,432 pixels. Width × height = 1,024 × 768 = 786,432.

5. 5

   What is colour depth?

   Model answer

   Colour depth is the number of bits used to store the colour of each pixel.

6. 6

   How many colours can an image with a colour depth of 1 bit show?

   Model answer

   A colour depth of 1 bit gives two colours. Each pixel is either 0 or 1, usually white or black.

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