Binary to Bitmap Conversion

For a simple black-and-white image with a colour depth of 1 bit, each pixel is represented by one binary digit: either 0 or 1. These two values can represent the two colours. In the example below, the colour key is 0 = black, 1 = white.

The codes describe colours, not a number to convert into denary. For example, 0101 describes four separate pixels: black, white, black, white.

Set up the grid

Consider this binary pattern, with each line representing one row of pixels:

0101
1010
0101
1010
0101

There are four bits in each row and one bit per pixel, so the image is four pixels wide. There are five rows, so it is five pixels high. Draw a grid with four columns and five rows. Each square represents one pixel.

Fill the pixels in reading order

Start at the top-left pixel. Read the first row of data from left to right, filling one square for each bit:

• The first bit is 0, so shade the first square black.
• The second bit is 1, so leave the second square white.
• The remaining bits, 0 and 1, make the third square black and the fourth white.

Then move to the leftmost square of the second row. Its data is 1010, so this row becomes white, black, white, black. Continue across each row, working from the top of the grid to the bottom.

The completed image is a checkerboard pattern. Rows one, three and five start with black; rows two and four start with white. Every bit has been used once, and every grid square has a colour.

When the data is one continuous string

Sometimes the data is supplied without line breaks. Use the given image width to identify where each row ends. For a one-bit image four pixels wide, take the first four bits as the top row, the next four as the second row, and continue in groups of four.

The row boundaries matter: they determine where each pixel belongs. After filling the grid, check each row against its corresponding data, using the colour key to confirm every square.