16 bit colour is stored in order, from left to right and top to bottom.
Each 2 bytes represents one pixel. If you rip each 2 bytes into an array of (16 bit words) Those (16 bit words) are as good as an ID you can store in a table.
Also you could cut down the number of colours to 256 by using a lookup table of 256 colours, and rounding each colour down to it's nearest colour in your table.
Maybe this will help.
Each 2 bytes represents one pixel. If you rip each 2 bytes into an array of (16 bit words) Those (16 bit words) are as good as an ID you can store in a table.
Also you could cut down the number of colours to 256 by using a lookup table of 256 colours, and rounding each colour down to it's nearest colour in your table.
Maybe this will help.