Stretch tasks Storing Images

Round 1: Quiz Blitz

1. The smallest single point of colour in a bitmap image Pixel is short for picture element. Each one holds one colour value.
2. The number of pixels in an image Resolution is a count of pixels, usually width by height, such as 1920 x 1080.
3. 16 n bits give 2 to the power n colours: 2 to the power 4 is 16.
4. False Colour depth is bits, not colours. 4 bits give 16 colours.
5. Four times larger Twice as wide and twice as tall means four times as many pixels.
6. Width and height; Colour depth Metadata is data about the data: dimensions, colour depth, date, camera and more.
7. So software can rebuild the grid of pixels correctly Without the width, a long list of colour values could not be arranged into rows.
8. 100 1 x 10 x 10 = 100 bits.
9. Three times larger Each pixel needs 24 bits instead of 8, which is three times as many.
10. 1 bit → 4 bit → 8 bit → 24 bit 2, 16, 256 and 16,777,216 colours.
11. Pixelated With too few pixels for its size, the individual squares become visible.
12. True That is why hex colour codes have six digits: two per channel.

Round 2: Quick Fire

1. • More pixels, so more detail and better quality
   • A larger file size
   Model answer

   There are more pixels, so the image shows more detail. But there is more data to store, so the file is larger.

2. • It records the width, height and colour depth
   • So the software can rebuild and display the pixels correctly
   Model answer

   Metadata records the image's width, height and colour depth, so the software can rebuild the grid of pixels and display the image correctly.

3. • 8 bits
   • Because 2 to the power 8 is 256
   Model answer

   Its colour depth is 8 bits, because 2 to the power 8 is 256.

4. • Fewer colours, so lower quality or banding
   • A smaller file
   Model answer

   Fewer colours are available, so quality is lower and smooth gradients can show banding. The file is smaller.

Round 3: Big Think

1. • 8 x 500 x 400 = 1,600,000 bits
   • Divide by 8: 200,000 bytes
   • Divide by 1000: 200 KB
   • Add the metadata: 201 KB
   Model answer

   8 x 500 x 400 = 1,600,000 bits. 1,600,000 / 8 = 200,000 bytes. 200,000 / 1000 = 200 KB. Adding the 1 KB of metadata gives 201 KB.

2. • Resolution is the number of pixels, width by height
   • Higher resolution gives more detail
   • Higher resolution means more data, so a larger file
   • Doubling width and height makes the file four times bigger
   • Colour depth is the number of bits per pixel
   • More bits give more colours: n bits give 2 to the power n
   • More bits per pixel make the file bigger in proportion
   Model answer

   Resolution is the number of pixels in the image, given as width by height. A higher resolution gives more detail, so the image looks sharper and is less likely to look pixelated, but there is more data to store, so it gives a larger file: doubling both the width and the height makes the file four times bigger. Colour depth is the number of bits used to store the colour of each pixel. More bits give more colours, because n bits give 2 to the power n colours, so 24 bits give over 16 million colours and smoother gradients. But every pixel then needs more bits, so the file grows in proportion.

This or That

1. 8-bit colour 8 bits give 256 colours. 4 bits give 16.
2. 2 One bit is a 0 or a 1, so two colours, usually black and white.
3. Doubling width and height Twice as wide and twice as tall is four times the pixels. Doubling the colour depth only doubles the file.
4. Two hex digits for each of red, green and blue 24-bit colour is 8 bits per channel, and 8 bits is two hex digits.
5. The camera model used Metadata is data about the image, such as its size, date and camera, not the pixel data.
6. No: it is a count of pixels Resolution is width x height in pixels. More pixels can show more detail.
7. 8 2 to the power 3 is 8.
8. 1920 x 1080 pixels More pixels can describe more detail.

Memory Match

• A 4 Pixel: One point of colour in a bitmap
• B 3 Resolution: The number of pixels in an image
• C 1 Colour depth: Bits used for each pixel's colour
• D 6 Metadata: Data about the data, such as width
• E 2 Bitmap: An image stored as a grid of pixels
• F 5 Pixelated: Blocky when enlarged too far

Sort It

1. Bigger Adding metadata Metadata is stored in the file too, so it adds a little.
2. Smaller Cropping it to half its width Half the pixels, so half the pixel data.
3. Bigger Raising the colour depth from 8 to 24 bits Each pixel now needs three times the bits.
4. Smaller Reducing the colour depth from 24 to 8 bits Each pixel needs a third of the bits.
5. Smaller Halving the width and the height A quarter of the pixels means a quarter of the data.
6. No change Zooming in on it Zooming changes the view, not the stored pixels.
7. No change Copying it to a memory stick A copy holds exactly the same data.
8. Bigger Going from 1-bit to 2-bit colour Twice the bits per pixel doubles the pixel data.
9. Bigger Doubling the resolution More pixels means more data to store.
10. No change Printing it Printing makes a paper copy and leaves the file alone.
11. Smaller Converting it to 1-bit black and white One bit per pixel is the smallest colour depth.
12. No change Viewing it on a bigger screen The file is the same: the screen just displays it larger.