It's Primary 3 maths...
your camera max pixel size is 3168 x 4752 , 4R is 4"by 6", both are 2:3 isn't it?
3168 : 4752 ====> 4:6 =====> 2:3
3168/4752 = 0.6666666 = 2/3.
(so back to Primary 3 maths... 3168/2 = 1584. So now 4752/1584 = 3. Bingo, it's 2/3)
4r = 4/6 = 0.666666 = 2/3
In other words, your base factor/dimensions/aspect ratio is 2/3 so just send and develop.
That mean i don need to crop also i will get a 4R photo izzit ?? Cos my max pixel is 3168 : 4752 = 4 : 6 = 2 : 3 all are = to 0.666666666666666. In other ward if i wanted to change the perspective of my photo, i still can crop to a 4R size photo rite ??? because my actual pixel size is big enough for me to crop it to a smaller size pixel but still i will get a 4R size photo if i crop to a ratio of 4:6 or 2:3 ??