Wirebook › Bonus lesson
Can a blocky picture be made sharp again?
In films, a detective says “enhance!” and a blocky picture turns sharp. Can a real computer do that? Play the mystery blob game, try the enhance button yourself, then find out why blurring or pixelating a password in a screenshot does not hide it. Everything happens in your browser.
Why the blocks can't be turned back
Making a picture blocky is a one-way trip. Take a patch of 256 pixels: some brown teeth, some white sky, some green skin. Averaging them gives one muddy colour. Lots of different patches give exactly that same muddy colour, so when you only have the average, there is no way to know which patch it came from. That is why the patches you bought in the game had to be copied from the original: the detail wasn't hiding inside the block, it was thrown away. It is the same idea as lossy compression in the suitcase lesson.
Some newer apps use AI to “upscale” photos, and the results can look amazingly sharp. But the AI has not found the missing pixels. It has guessed what a face or a sign usually looks like and painted that in. That is fine for a fun wallpaper and wrong for evidence: an upscaled number plate can show letters that were never there.
Why pixelating isn't a safe way to hide things
The snoop never “un-pixelated” anything. They did something simpler: pixelation is a recipe anyone can repeat, so they wrote every possible PIN in the same lettering, pixelated each one with the same squares, and looked for the one that matched. A 4-digit PIN only has 10,000 possibilities, and a computer tries them all in a blink. Short words, names and card numbers with only a few hidden digits are just as guessable. Blurring has the same weakness.
A few more honest details
- Resolution. How many pixels a picture has is its resolution. Zooming in on a phone photo shows bigger pixels, not new ones.
- Real snoops need to match the lettering. This page's snoop knows the exact font and square size. In real screenshots that is often easy to work out, because screens use common fonts and apps pixelate in predictable squares.
- Big squares help a little, not enough. With huge squares several PINs can make the same blob, but the snoop still goes from 10,000 possibilities to a short list.
Grown-up twins: Tooltern's image compressor (resize a photo and compare before and after with a wipe slider), the guide to megapixels vs file size, and the photo metadata viewer, because a picture can give away more than what you can see.