What's covered
Key facts
Bitmap File Size
A 100 × 100 image at 1-bit colour depth = 100 × 100 × 1 = 10,000 bits.
Colour Depth
1-bit colour depth gives 2 colours, typically black and white.
Pixels and Resolution
A 1920 × 1080 image has roughly 2 million (about 2.07 megapixel) pixels.
Bitmap File Size
A 100 × 100 image at 8-bit colour depth = 100 × 100 × 8 = 80,000 bits.
Colour Depth
24-bit colour depth ("True Color") gives about 16.7 million colours, with 8 bits each for red, green, blue.
Pixels and Resolution
A bitmap image is made of a rectangular grid of coloured pixels.
Bitmap File Size
A 200 × 200 image at 4-bit colour depth = 200 × 200 × 4 = 160,000 bits.
Colour Depth
8-bit colour depth gives 256 colours per pixel.
Pixels and Resolution
Doubling resolution in both dimensions roughly quadruples the file size (×2 width × ×2 height = ×4 pixels).
Bitmap File Size
A 50 × 50 image at 8-bit colour depth = 50 × 50 × 8 = 20,000 bits.
Practice questions with answers
A taste of the 25 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
What is the formula for bitmap file size in bits?
- •Resolution divided by colour depth
- •Width plus height plus colour count
- •Width times height divided by sample rate
- ✓Width times height times depth
What does colour depth mean?
- ✓Bits used per pixel
- •Bytes used to store the whole file
- •Number of pixels per inch
- •Total number of pixels in an image
A 1920×1080 image has how many pixels?
- ✓About 2 million pixels
- •About 20 million pixels
- •About 200 million pixels
- •About 200 thousand pixels
100×100 image at 1 bit. Size in bits?
- •100,000 bits
- ✓10000 bits
- •One thousand bits
- •Ten bits
1-bit colour depth gives how many colours?
- •Eight colours like a flag
- •Four colours like a poster
- •Sixteen colours like early Windows
- ✓Two colours (black and white)
What does higher resolution usually mean?
- •Lower quality with bigger file
- ✓Sharper image but bigger file
- •Sharper image with smaller file
- •Smaller file with sharper image
Three minutes a day. Knowledge that sticks.
Practise all 25 Representing Images questions with spaced repetition, so what you revise today is still there in the exam. Free to use, no card needed.