I wrote a quick python utility to aid in the generation of bitmaps for the 16x16 matrix driver. The utility can generate / print a code friendly array of bytes (encoded in binary) that can be used as a bitmap. This bitmap can them be combined with other bitmaps in external memory or other memory space (more than likely code store space) and then indexed to be sent over to the display driver.

The utility does take a cfg file so you can change the text per button. Take a look at the github repo for the tool.

Below is a pic of the tool as well as all of the bitmaps I generated / needed for the word clock.

static const uint8_t bitmaps[BITMAP_CT][BITMAP_SZ] = {
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b11111101,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11100000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00011100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b00000000,0b00000000,0b00000000,0b11110000,0b00000001,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b00000000,0b00000000,0b00000000,0b00001111,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b00000000,0b00000000,0b11110000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b11100000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b00000000,0b11000000,0b00000111,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b00000000,0b00011111,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00000000,0b00011110,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b11000000,0b00000001,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000001,0b00111111,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11011000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00001111,0b01111111,0b11100000,0b00000001,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00001111,0b01111111,0b00000000,0b00000000,0b00000111,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00001111,0b00000000,0b00000000,0b00000000,0b11111000,0b00000011},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00001111,0b01111111,0b00000000,0b11111100,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00001111,0b01111111,0b11100000,0b11111101,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00001111,0b00000000,0b00001111,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01100000,0b01111111,0b11100000,0b11111101,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01100000,0b01111111,0b00000000,0b11111100,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01100000,0b00000000,0b00000000,0b00000000,0b11111000,0b00000011},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01100000,0b01111111,0b00000000,0b00000000,0b00000111,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01100000,0b01111111,0b11100000,0b00000001,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111000,0b00000000,0b11100000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00001110,0b00000000,0b00000000,0b00000000,0b11111111,0b00000011,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00001110,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11111110,0b00001101,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b11111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b11111111,0b00000001,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11111100,0b00111111,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00111111,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b10000000,0b11111111,0b00000000,0b11111000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11111000,0b11111111,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11100000,0b00000011,0b11111111,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00001110,0b00000000,0b11111111,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00001110,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11111110,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b00001110,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b11111110,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000},
{0b00000000,0b00000000,0b00000000,0b00000000,0b11101110,0b00000011,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b01111100,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000,0b00000000}
};