These are the images that note where the columns are and where the judgement line should be at. The down.png images represent when the key is pressed, and the up.png images represent when the key is not pressed.
The files should be formatted as {key}k-{lane}-{state}.png. Lanes are numbered from left to right.
Examples:
1k-1-down.png, 1k-1-up.png4k-1-down.png -> 4k-4-down.png, 4k-1-up.png -> 4k-4-up.png5k-1-down.png -> 5k-5-down.png, 5k-1-up.png -> 5k-5-up.png7k-1-down.png -> 7k-7-down.png, 7k-1-up.png -> 7k-7-up.png