Convert binary data into a bitmap image. Given a binary pattern that…

The idea

A simple bitmap stores each pixel as a binary value, and a binary pattern can be converted back into a picture by mapping each value to a shade or colour. For a one-bit-per-pixel image, 0 and 1 represent two colours, so the pattern is laid out row by row: the first group of bits fills the top row left to right, the next group fills the second row, and so on. The width of each row must be known, because the same string of bits gives different pictures depending on how many bits form a row. To draw the image, split the binary into rows of the stated width, then shade each cell according to its bit value.

What earns the marks

• Splits the binary pattern into rows using the stated image width.
• Maps each bit value to the correct shade or colour according to the given key.
• Draws the pixels in the correct order, filling each row left to right before moving to the next row.
• Selects the grid whose shaded cells match the binary pattern exactly.
• Recognises that the row width determines how the bits are arranged into a picture.

Common mistakes and how to put them right

• Reading the bits down columns instead of across rows.

  Put it right: Fill each row left to right before starting the next row.

• Ignoring the stated row width and splitting the pattern arbitrarily.

  Put it right: Use the given width so each row has the correct number of pixels.

• Reversing the mapping of 0 and 1.

  Put it right: Apply the supplied key consistently to every bit.

Exam tips

• Write the row width above the pattern and mark a break every width bits before drawing.
• Apply the 0/1 colour key to one cell at a time and check each row against the original bits.
• Compare your finished grid with each option cell by cell rather than judging by overall appearance.