Image File Size Flashcards

1️⃣ Familiarise yourself with the flashcards:

  • Look through all the flashcards to see what's on both sides.
  • Make sure you understand the information on each card. If something's unclear, click the link to the revision notes at the bottom of the page for more details.

2️⃣ Test yourself:

  • Look at the question or prompt on each card and try to remember the answer before flipping it over.
  • Check the answer and make a note of any cards you find challenging and need to go over more.

3️⃣ Consistently Review and Practice:

  • Use spaced repetition: spend more time on the cards you struggle with and go over them more often.
  • Regularly review all the flashcards to help you better understand and retain the information over time.

Note: We may include questions that have multiple correct answers. It's useful to remember specific examples to understand these concepts better.

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What is image file size?

The amount of storage space an image uses, measured in bits, bytes, KB or MB.

Which two things mainly set the size of an uncompressed bitmap image?

The number of pixels (resolution) and the colour depth (bits per pixel).

What does resolution mean for an image?

The total number of pixels: width × height.

What does colour depth (bits per pixel) mean?

How many bits are used for each pixel. More bits allow more colours and a bigger file.

What is the formula for an uncompressed bitmap’s size in bits?

File size (bits) = width × height × colour depth (bits per pixel).

How do you convert an image size from bits to bytes and kilobytes (KB)?

Divide by 8 to get bytes, then divide by 1024 to get KB.

Calculate the size of a 128 x 128 image at 8 bpp.

128×128=16,384 px; ×8=131,072 bits; ÷8=16,384 bytes; ÷1024=16 KB.

Calculate the size of a 256 x 256 image at 24 bpp.

256×256=65,536 px; ×24=1,572,864 bits; ÷8=196,608 bytes; ÷1024=192 KB.

Calculate the size of a 320 x 240 image at 8 bpp.

320×240=76,800 px; ×8=614,400 bits; ÷8=76,800 bytes; ÷1024=75 KB.

If you double both the width and the height, what happens to file size (same colour depth)?

It becomes four times bigger, because the pixel count quadruples.

If you double the colour depth, what happens to file size (same resolution)?

It doubles, because each pixel has twice as many bits.

Why might a saved image file differ from your calculated size?

File headers, metadata, padding and compression can add or reduce size.