Christmas Bitmap Challenge

1. Create your bitmap

Choose a bitmap size and click the pixels to create your Christmas picture.

Bitmap size:

Choose a colour

0 Coloured pixels

256 Total pixels

256 Bits at 1-bit colour

At 1-bit colour depth, every pixel requires one bit. Therefore the number of bits is the same as the number of pixels.

What is a bitmap?

A bitmap image is made from a grid of tiny pixels.

Each pixel needs information telling the computer what colour it should be.

Computers store this information using binary.

Think: If your image is 16 x 16 pixels and each pixel uses one bit, how many bits are required?

16 x 16 = 256 bits

Christmas Challenges

Challenge 1 - Christmas Icon Create a recognisable Christmas object using pixels. Try creating a Christmas tree, star, present, snowman, Santa or reindeer.

Challenge 2 - Binary Detective Look at the binary representation. Can you work out which rows contain parts of your picture?

Challenge 3 - Copy the Bitmap Give your binary data to another student. Can they recreate your picture without seeing the original?

Challenge 4 - Change the Resolution Create the same type of image using 8 x 8, 16 x 16 and 32 x 32 pixels. How does increasing the number of pixels affect the amount of information required?

Challenge 5 - Colour Depth A black-and-white bitmap can use one bit per pixel. What happens when we want to store multiple colours?

Two bits can represent four different values:


        00    01    10    11

Challenge 6 - Extension Imagine a 1920 x 1080 image using 24-bit colour. How many bits would be needed to store the image without compression?

2. Your image in binary

Each row of your bitmap is converted into a sequence of 0s and 1s.

3. What does the binary mean?

For a simple black-and-white bitmap:

0 means the pixel is OFF.

1 means the pixel is ON.

For example, a row might contain:

00111100

Each number represents one pixel. The eight binary digits therefore describe eight pixels in one row of the image.

Colour and Binary

Real bitmap images can contain many colours. Computers use more bits per pixel to represent more possible colours.

Bits per pixel	Possible colours
1 bit	2
2 bits	4
4 bits	16
8 bits	256
24 bits	16,777,216

Key idea: More bits per pixel allow more colours, but also require more storage space.

Christmas Card

Turn your bitmap into a printable Christmas card. Your bitmap and custom message will appear on the printed card.

Message on your card

The card is designed to be printed on one sheet of A4 in landscape orientation. The card occupies the right-hand half of the page so it can be folded.