4.5.6.4 Bitmapped graphics Quiz: AQA Computer Science, Unit 5

The 20 questions

1. What is a pixel?

   • A unit that measures the volume of sound in a recording, held as a level in decibels
   • The smallest element of a bitmap image, holding a colour value
   • A geometric shape stored as a set of coordinates that define its outline and fill colour
   • A compressed block of image data, grouped so that a whole region is stored as one value

2. What is colour depth in a bitmap?

   • The number of bits stored for each pixel
   • The number of pixels across the image
   • The number of dots per inch
   • The total file size in bytes

3. How does the specification define resolution for a bitmap?

   • The size of the file in kilobytes after compression has been applied to the bitmap data
   • The number of colours available in the palette used by an indexed colour bitmap image
   • The number of dots per inch, where a dot is a pixel
   • The number of bits stored for each pixel, which sets how many colours each pixel can show

4. How is the size of an image in pixels calculated?

   • Width in pixels multiplied by height in pixels
   • Resolution divided by height
   • Width in pixels plus height in pixels
   • Colour depth multiplied by width

5. Which metadata is typically stored in a bitmap image file?

   • The width, height and colour depth
   • A list of the sound samples
   • The compression ratio of an audio track
   • The vector coordinates of every shape

6. What changes when the number of bits per pixel increases?

   • The width of the image
   • The resolution in dots per inch
   • The number of pixels in the image
   • The number of colours each pixel can show

7. How many colours can one pixel show with 8 bits of colour depth?

   • 128
   • 8
   • 64
   • 256

8. An image is 800 x 600 pixels at 24 bits per pixel. How many bytes does it need, ignoring metadata?

   • 1,440,000 bytes
   • 11,520,000 bytes
   • 1,152,000 bytes
   • 480,000 bytes

9. A 1920 x 1080 image has 8 bits per pixel. How many bytes does it need, ignoring metadata?

   • 2,073,600 bytes
   • 1,036,800 bytes
   • 2,073,600 bits
   • 16,588,800 bytes

10. A 100 x 100 image has 1 bit per pixel. How many bits does it need?

    • 20,000 bits
    • 1,000 bits
    • 10,000 bits
    • 100 bits

11. An image is 3 inches wide at 300 dpi. How many pixels wide is it?

    • 100 pixels
    • 900 pixels
    • 3,000 pixels
    • 300 pixels

12. An image's resolution doubles from 150 dpi to 300 dpi at the same physical size, with the same colour depth. How does the file size change?

    • It becomes eight times larger, because both dimensions double and the colour depth doubles as well
    • It becomes four times larger, since both width and height in pixels double
    • It becomes twice as large, because the extra resolution only increases one dimension of the picture
    • It stays the same size, since dpi describes how the image prints and does not change the pixel count

13. Halving the colour depth from 24 bits to 12 bits, with the same pixel count, does what to storage?

    • It has no effect, since colour depth does not affect storage
    • It reduces storage by a quarter
    • It halves storage only in JPEG files
    • It halves the storage, since storage equals pixels times colour depth

14. A 4 x 4 pixel image has 8 bits per pixel. How many bytes does it need, ignoring metadata?

    • 16 bytes
    • 4 bytes
    • 128 bytes
    • 8 bytes

15. How many pixels are in a 640 x 480 image?

    • 307,200
    • 1,228,800
    • 64,000
    • 120,480

16. A 1024 x 768 image has 16 bits per pixel. How large is it in KiB, ignoring metadata?

    • 768 KiB
    • 1536 KiB
    • 3072 KiB
    • 1024 KiB

17. Why might an image file be larger than the simple storage calculation predicts?

    • Pixels are always stored with extra bits for a sign, so every pixel needs one more bit than shown
    • Resolution in dpi adds a fixed number of bytes to each pixel that is stored in the file
    • It may include metadata such as width, height and colour depth, which the calculation ignores
    • Bitmaps are stored as text, which doubles the size of the file compared with binary storage

18. Why does the pixel count, rather than dpi, determine the stored size of a bitmap?

    • Dpi is used to calculate the file size in bytes directly, without any reference to the pixels
    • Dpi determines the number of bits per pixel, so a higher dpi value always needs more storage
    • Storage depends on the number of pixels and bits per pixel, and dpi only describes how the image prints
    • Pixel counts never affect the storage size, because the file size depends only on the printer

19. What happens to the pixels when a bitmap is scaled up a great deal?

    • The image is converted into vector graphics
    • The colour depth doubles for each enlargement
    • New detail is added automatically, so the image stays sharp
    • Each pixel becomes a visibly larger block, so the image looks pixelated

20. An image has 2^20 pixels at 4 bits per pixel. How many bytes does it need, ignoring metadata?

    • 1,048,576 bytes
    • 524,288 bytes
    • 4,194,304 bytes
    • 2,097,152 bytes

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