# Symmetrical Pixel Puzzles

In these symmetrical colour by number pictures you are only given the numbers for half the pixels. Use symmetry to work out the rest of the numbers and so the rest of the picture.

This can also be used as an introduction to the idea of compression – if you know something about the properties of a picture you can reconstruct the image despite storing fewer numbers!

## Instructions

Some squares have a number that tells you the colour to colour in that square. Look up the colours in the key. Other squares have no number. Work out what colour they are by symmetry.

So, for example with a colour lookup table  1 Blue, 2 Red  a row with numbers (where _ means blank)  1 1 1 1 1 2 2 2 _ _ _ _ _ _ _ _  would mean colour five pixels blue and then by symmetry three pixels red,  then three pixels red and five pixels blue.

Complete them in either of two ways (two algorithms). Either:

1.  Use symmetry to first fill out the rest of the grid of numbers to create a normal colour by number pixel, OR
2. Colour in the numbers given, then copy the colours on to the other side.

## Resources

Below are lots of downloadable sheets to print off, with the answers visible so you can see what the pictures are – or send kids to either the individual pages or our “A bit of cs4fn” website where they can download them directly themselves without seeing the answers first.

Alternatively if you do not have a printer and want to do them online, then here is a spreadsheet with all created so far in.

To colour cells in a spreadsheet you need to select a cell and then paint its background colour. Exactly how you do this will depend on the spreadsheet program you are using.

Here are Colour by Number Pixel Puzzle Picture sheets and solutions that you can download.

Mini-beast Pictures

Butterfly

Beetle

Christmas Picture: Snowman

by Elisa Huen

Easter Picture: Chick by Elisa Huen