fixed point precision

[Abdallah . (Company: Home) (my_name)]

Peace!
I want ask about the number of bits shoud I use in an fixed_point number 
to obtein the good precision, precision of distance eclidean.
some detail:
I want to determine an vector of foor element VECT[MOY1,MOY2,MOY3,MOY4], 
each element is the moyen of one quart of matrix of (64*64), the matrix' 
element value varies (0-255)'''it's pixel valor'''
--> the result of division (MOY1=SUM/Nbits) has 8 bits in the integer 
part;
Question: how many bits of fractional part shout I use to get the good 
result (result of euclidean distance between two vector 
VECT1[MOY11,MOY12,MOY13,MOY14] and VECT[MOY21,MOY22,MOY23,MOY24])..
thank you....peace:

[Duke Scarring (Guest)]

Abdallah      wrote:
> about the number of bits shoud I use in an fixed_point number
> to obtein the good precision
You have to define the precision. Independed if you use fixed point or 
integer number format.

The number of bits depends on your dynamic range:
http://en.wikipedia.org/wiki/Dynamic_range

Roughly: NoBs = SNR / 6

eg.: 16 Bit = 96 dB / 6

Duke

[Michael W. (Guest)]

Why would you consider to be the DR at 16 Bits not to be 96dB but 
96dB/6?

[... (Guest)]

You wanted a GOOD precission in the result, right? then divide it by 6 
:-)

[Duke Scarring (Guest)]

Markus Wagner wrote:
> Why would you consider to be the DR at 16 Bits not to be 96dB but
> 96dB/6?
Read carefully:
 number of bits * 6 dB = dynamic range