[Octave-bug-tracker] [bug #54567] median(uint8) gives bad results

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?54567>

                 Summary: median(uint8) gives bad results
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Fri 24 Aug 2018 03:50:40 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Etienne de Foras
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.4.1
        Operating System: Microsoft Windows

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Details:


If I define:

u= [1 140 140 255];  
u8=uint8(u);

then median(u)=140 (correct)
but  median(u8)=128 (incorrect, should be 140)


The bug disappear with odd size data, the median with even size data is
computed as (140+140)/2, but with saturation to 255 due to uint8 type and then
divided by two ->127 (or 128 with rounding).
We may use the type int32 or double for the sum and division by 2 and then
convert back to uint8


(Thanks for GNU Octave !)




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