Keep every bit, or drop what hides

Computing · Computer Systems · ages 15-16

Name ______________________ Date ____________

In run-length encoding, what does the first number always count?
- Red pixels
- White pixels
- Rows
What does lossless compression promise?
- Files shrink tenfold always
- Dropped detail returns later
- Every bit returns exactly
A row opens with a red pixel. What is its first run count?
- 0
- 1
- 15
Which kind suits program code?
- Lossy, since code forgives drops
- Lossless, since each bit must return
- Either, since code is tiny
The counts 3, 2, 5, 2 and 4 describe one row. How many pixels does the row hold?
Answer: ______________
Which kind suits holiday photos for sharing?
- Lossy, since eyes forgive the trims
- Lossless, since photos need ZIP
- Neither, since photos resist packing
Lossy detail, once dropped, can be rebuilt from the small file.
Circle one: True False
A friend re-saves one lossy photo through ten edits and mourns the mush. What is the lesson?
- Re-save more often for sharpness
- Lossy files heal with time
- Keep a lossless master and export copies

Answer key

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

White pixels · Run counts always open with the whites.
Every bit returns exactly · Lossless packing keeps every bit, so the file round-trips perfectly.
0 · Counts always start at white, so a red opener records zero whites.
Lossless, since each bit must return · Code with a dropped bit is broken code, so nothing may go missing.
16 · Adding the runs gives 3 plus 2 plus 5 plus 2 plus 4, which is 16.
Lossy, since eyes forgive the trims · A photo at half size still reads fine to human eyes.
False · Dropped detail is gone for good. Only lossless round-trips.
Keep a lossless master and export copies · Each lossy re-save grinds quality down, so guard the master.