Nonograms

Each square in the grid has three possible states, which you can cycle through by tapping them. A square that is filled is included in the picture, while a white square is not. If you're sure that a square should not be part of the picture, you can mark it with an X. The game is finished when you've created a picture that satisfies the row and column requirements. In some cases, more than one solution can exist for a particular puzzle.

You can adjust the size of the grid, and choose show or hide the timer. The smallest allowable grid size is 2x2, and you can generate as large a grid as you'd like (above 30x30 is difficult to work with on most screens). You may also choose a density of the picture. This is the ratio of filled to empty squares in the completed picture. Choosing a lower density will create a more challenging puzzle.