SPEC:
Read 1376 byte binary file into uint16_t array
overwrite item[16] with dec<7360> = 0X1cc0
overwrite item[22] with dec<4912> = 0X1330
Write file to disk


sub prefix_hdr()  {
    $hsize=1376;  # Size of 16-bit grayscale tif header
    $hfn='d:/pic/misc/gray.3689x2462.hdr';  # Md5 ~29992
    $brfn='6s-254550.7360x4912.blue.raw';  # photoshops
    $rsize=-s $brfn;
    $mutant='blue.7360x4912.tif';
    open(H, "<$hfn");  binmode H;
    $bread=read(H, $hdr, $hsize);  close H;
    printf("Read $bread B from $hfn\n");
    @rgb=unpack("S*", $hdr); # RAW RGB UShort array
    printf("RGB[16]=%hu, [22]=%hu\n", $rgb[16], $rgb[22]);
    $rgb[16]=pack("S", 7360);  # Overwrite 3689 with 7360
    $rgb[22]=pack("S", 4912);  # 2462 -> 4912
    printf("FIXED?  RGB[16]=0X%04hu, [22]=%hu\n", $rgb[16], $rgb[22]);
}
Read 1376 B from d:/pic/misc/gray.1376b.3689x2462.hdr
RGB[16]=3689, [22]=2462     <<  PERFECT!
Argument "&#9492;^\" isn't numeric in printf  
Argument "0^S" isn't numeric in printf
FIXED?   RGB[16]=0X0000, [22]=0    <<<<<<WRONG
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