According to a anecdotal test on one of the images found elsewhere in this thread, JPEG comression at 80% quality can chop a factor of 16 off the size of a 24bp

According to a anecdotal test on one of the images found elsewhere in this thread, JPEG comression at 80% quality can chop a factor of 16 off the size of a 24bpp .bmp file. 384 / 16 = 24bits per [64x64x4-] array value. Integer range of 32bit float is 2^24. So "literally just a jpeg packed into 16K floats" is a option.