time   calls  line
                  1 function tf = isjp2(filename)
                  2 %ISJP2  Returns true for a JPEG2000 file or code stream.
                  3 %    TF = ISJP2(FILENAME) returns true if FILENAME refers to a JPEG-
                  4 %    2000 file or code stream.
                  5 
                  6 %    Copyright 2008 The MathWorks, Inc.
                  7 %    $Revision: 1.1.6.1 $  $Date: 2008/05/14 22:02:50 $
                  8 
                  9 
                 10 % Page 535 of "JPEG 2000 Image Compression Fundamentals, Standards, and 
                 11 % Practice" identified the first 4 bytes of a JPEG 2000 code stream as 
                 12 % consisting of the markers
                 13 %
                 14 % SOC "start of code stream" FF4F ==> [255 79]
                 15 % SIZ "image and file size"  FF51 ==> [255 81]
                 16 %
                 17 % For a JP2 file, a four-byte preamble (0x000C == [0 0 0 12]) and a
                 18 % signature box must come first.  The box type is 'jP  ' == 0x6A502020 ==
                 19 % [106 80 32 32].  This is followed by the contents of the box, 0x0D0A870A
                 20 % == [13 10 135 10].
                 21 %
                 22 % This makes a signature of 12 bytes,
                 23 %
                 24 % [0 0 0 12 106 80 32 32 13 10 135 10].
                 25 
                 26 % Magic values.
            12   27 jp2sig = [0 0 0 12 106 80 32 32 13 10 135 10]'; 
            12   28 jpcsig = [255 79 255 81]'; 
                 29 
                 30 % Open the file.
            12   31 fid = fopen(filename, 'r'); 
            12   32 if (fid < 0) 
                 33     tf = false;
                 34     return;
                 35 end
                 36 
                 37 % Read the first 12 bytes.
            12   38 [filesig, count] = fread(fid, 12, 'uint8'); 
            12   39 fclose(fid); 
                 40 
            12   41 if (count ~= 12) 
                 42     tf = false;
                 43     return;
                 44 end
                 45 
                 46 % Is it a codestream wrapped in a box?
            12   47 if (isequal(jp2sig, filesig)) 
                 48     tf = true;
                 49     return
                 50 end
                 51 
                 52 % Is it just a code stream?
            12   53 if (isequal(jpcsig, filesig(1:4))) 
                 54     tf = true;
                 55     return
                 56 end
                 57 
                 58 
                 59 % If we're here, then it's probably not a JPEG 2000 file or codestream.
            12   60 tf = false;