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Pictures made of tiny squares

Computing · Computer Systems · ages 14-16

Name ______________________ Date ____________

Resolution controls how many pixels make up the picture.
Circle one: True False
What is a pixel?
- A whole photo
- A tiny square
- A file type
What does colour depth control?
- Bits per pixel
- How wide the screen is
- How fast the picture prints
An image's colour depth doubles from 8 to 16 bits, and its width and height stay the same. What happens to its uncompressed size?
- It stays the same
- It halves
- It doubles
A 100 by 100 image uses 8-bit colour. How many bits does its pixel data take before compression?
Answer: ______________
What happens when a picture is blown up past its resolution?
- It looks blurry or blocky
- It gains true detail
- Its file shrinks
A 12 by 12 two-colour icon uses 1 bit per pixel. How many bits does it take before compression?
- 24 bits
- 144 bits
- 12 bits
A 30 by 20 image uses 2-bit colour. How many bits does it take before compression?
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

True · More pixels means higher resolution and a sharper picture.
A tiny square · Pictures are grids, and each grid square is one pixel.
Bits per pixel · Depth sets the bits per pixel, which sets the colour count.
It doubles · The pixel count stays the same and every pixel carries twice the bits, so the uncompressed size doubles.
80000 · 100 times 100 is 10,000 pixels, and 8 bits each gives 80,000 bits before compression.
It looks blurry or blocky · Each pixel must cover more space, and guessed colours look rough.
144 bits · The icon has 12 times 12, or 144, pixels. One bit per pixel gives 144 bits.
1200 · There are 30 times 20, or 600, pixels. At 2 bits per pixel, the image takes 600 times 2, which is 1,200 bits.