ConvGeneric by Roudoudou is a command line utility (windows, MacOS) to convert PNG to Amstrad CPC formats like sprites, tiles, complete screens... :

• Multimode support
• Software sprite conversion
• Tile extraction
• Tiled screens mode
• Metatile mode
• Screen conversion
• Hardware sprite extraction

Beware this utility can't reduce the number of colors, if you need this then use :

• Martine
• ConvImgCpc