jpeg-dpi.ps

%!PS

%================================================================================
% Test Card Maker tool to set JPEG DPI
%================================================================================

% gs -q -dNOSAFER -dNODISPLAY -o out.jpg -dDPI=n -- jpeg-dpi.ps in.jpg

false % no error
/.sort where { pop }{ (Error: missing -dNOSAFER option) = pop true } ifelse
/NODISPLAY where { pop }{ (Error: missing -dNODISPLAY option) = pop true } ifelse
/OutputFile where { pop }{ (Error: missing -o option) = pop true } ifelse
.shellarguments not count 3 lt or count -1 roll or {
    (Usage:) =
    (  gs -q -dNOSAFER -dNODISPLAY -o out.jpg -- jpeg-dpi.ps in.jpg) =
    (for a DPI of n (default 72):) =
    (  gs -q -dNOSAFER -dNODISPLAY -o out.jpg -dDPI=n -- jpeg-dpi.ps in.jpg) =
    quit
}{
    /InputFile exch def
    /IF InputFile (r) file def
    /OF OutputFile (w) file def
} ifelse
/DPI where { pop }{ /DPI 72 def } ifelse

18 string
0 1 17 { IF read { 3 copy put pop pop }{ (Error: not a JPEG file) = quit } ifelse } for
dup 6 4 getinterval (JFIF) ne { (Error: not a JPEG file) = quit } if
OF exch 0 13 getinterval writestring
OF 1 write % dpi
2 { OF DPI 256 idiv write OF DPI 256 mod write } repeat % X,Y dpi
{ IF read { OF exch write }{ exit } ifelse } loop
IF closefile
OF closefile
quit