1. A method comprising: obtaining input image data defining an input image that shows a row/column representation with rows and columns; using the input image data to obtain row data and column data; the row data uniquely indicating parts of the input image within an mth row of the row/column representation; the column data uniquely indicating parts of the input image within an nth column of the row/column representation; the row/column representation representing information for a combination of the mth row and the nth column; and using the row data and the column data to obtain content data indicating information represented by the row/column representation for the combination of the mth row and the nth column.