I was going to say that in a previous life, I was assimilated into the borg (Microsoft). I developed the 4x6 and 6x8 pixel fonts that you can use in the Command Prompt windows. (Choose "Raster Fonts" and select 4x6 or 6x8 for the size.) The 4x6 case would have 3x5 digits since the 4x6 measurement includes the space between columns and rows.
Getting maximum readability out of very few pixels can take a while, especially when you have to make è e é all distinct enough to read. I didn't convert them to hex or binary digits for C sketches but a script can do that easily enough.
Here are 3x5 digits.
struct cgr { char c, byte d[5] };
static cgr _digits =
{
'0', { 0x2, 0x5, 0x5, 0x5, 0x2 },
'1', { 0x2, 0x6, 0x2, 0x2, 0x7 },
'2', { 0x6, 0x1, 0x2, 0x4, 0x7 },
'3', { 0x6, 0x1, 0x2, 0x1, 0x6 },
'4', { 0x1, 0x5, 0x7, 0x1, 0x1 },
'5', { 0x7, 0x4, 0x6, 0x1, 0x6 },
'6', { 0x3, 0x4, 0x6, 0x5, 0x2 },
'7', { 0x7, 0x1, 0x2, 0x2, 0x2 },
'8', { 0x2, 0x5, 0x2, 0x5, 0x2 },
'9', { 0x2, 0x5, 0x3, 0x1, 0x6 },
};
I haven't double-checked it, but that seems right. To fit both digits in an 8x8 space, you would just shift the bits: (tens << 4 | ones).