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[EDIT] FILE: viewgif.ps

% Copyright (C) 2001-2019 Artifex Software, Inc.
% All Rights Reserved.
%
% This software is provided AS-IS with no warranty, either express or
% implied.
%
% This software is distributed under license and may not be copied,
% modified or distributed except as expressly authorized under the terms
% of the license contained in the file LICENSE in this distribution.
%
% Refer to licensing information at http://www.artifex.com or contact
% Artifex Software, Inc.,  1305 Grant Avenue - Suite 200, Novato,
% CA 94945, U.S.A., +1(415)492-9861, for further information.
%

% viewgif.ps
% Display a GIF file.

/read1			% <file> read1 <int>
 { read pop
 } bind def
/read2			% <file> read2 <int>
 { dup read1 exch read1 8 bitshift add
 } bind def

/readGIFheader		% <file> readGIFheader <dict>
 { 20 dict begin
   dup 6 string readstring pop
   dup (GIF87a) eq exch (GIF89a) eq or not
    { (Not a GIF file.\n) print cleartomark stop
    } if
   dup read2 /Width exch def
   dup read2 /Height exch def
   dup read1
   dup 128 ge /GlobalColor exch def
   dup -4 bitshift 7 and 1 add /BitsPerPixel exch def	%***BOGUS?***
   dup 8 and 0 ne /PaletteSorted exch def
   7 and 1 add dup /BitsPerPixel exch def
     1 exch bitshift /PaletteSize exch def
   dup read1 /BackgroundIndex exch def
   dup read1 15 add 64 div /AspectRatio exch def
   GlobalColor
    { PaletteSize 3 mul string readstring pop
      /GlobalPalette exch def
    } if
   currentdict end
 } bind def

/readGIFimageHeader	% <file> readGIFimageHeader <dict>
                        % Note: GIF header must be on dict stack
 { 10 dict begin
    { dup read1
      dup (!) 0 get ne { exit } if pop		% extension
      dup read1 pop
       { dup read1 dup 0 eq { pop exit } if { dup read1 pop } repeat
       } loop
    } loop
   (,) 0 get ne
    { (Not a GIF image.\n) print stop
    } if
   dup read2 /Left exch def
   dup read2 /Top exch def
   dup read2 /Width exch def
   dup read2 /Height exch def
   dup read1
   dup 128 ge /LocalColor exch def
   dup 64 and 0 ne /Interlaced exch def
   LocalColor
    { 7 and 1 add /BitsPerPixel exch def
      1 BitsPerPixel bitshift 3 mul string readstring pop
      /Palette exch def
    }
    { pop pop /Palette GlobalPalette def
    }
   ifelse
   currentdict end
 } bind def

/imageGIF		% <imagedict> imageGIF
 { /ImageOut where
    { pop
                % We know BitsPerComponent = 8, Decode = [0 255].
                % and there is only a single data source which is
                % either a filter or a string whose size is exactly
                % the width of the row.
      dup /DataSource get dup type /stringtype eq
       { ImageOut exch writestring
       }
       { pop dup /Width get string
         1 index /Height get
          { 1 index /DataSource get 1 index readstring pop
            ImageOut exch writestring
          }
         repeat pop pop
       }
      ifelse
    }
    { image
    }
   ifelse
 } bind def

/viewGIF		% <file|string> viewGIF -
 { save 20 dict begin
   /saved exch def
   dup type /stringtype eq { (r) file } if
   /F exch def
   /ImageOutFile where { /ImageOut ImageOutFile (w) file def } if
   F readGIFheader /Header exch def
     currentdict Header end begin begin
   VGIFDEBUG { Header { exch == == } forall (----------------\n) print flush } if
   F readGIFimageHeader /ImageHeader exch def
     currentdict ImageHeader end begin begin
   VGIFDEBUG { ImageHeader { exch == == } forall (----------------\n) print flush } if
   /D F
   <<	/InitialCodeLength F read1
        /FirstBitLowOrder true
        /BlockData true
        /EarlyChange 0
   >> /LZWDecode filter def

[/Indexed /DeviceRGB 1 BitsPerPixel bitshift 1 sub Palette] setcolorspace
   matrix currentmatrix
   0 1 3 { 2 copy get dup 0 ne { dup abs div } if 3 copy put pop pop } for
   setmatrix
   <<	/ImageType 1
        /ImageMatrix [1 0 0 -1 0 Height]
        /BitsPerComponent 8
        /Decode [0 255]
   Interlaced
    {	/Width Width   /Height 1
        /row Width string def
        /DataSource row
      >> /I exch def
      /inter		% <num> <denom> inter -
       { /denom exch def   /num exch def
         gsave
         /lines Height denom 1 sub add num sub denom idiv def
         0 1 lines 1 sub {
           Height exch denom mul num add sub
           I /ImageMatrix get 5 3 -1 roll put
           D row readstring pop pop
           I imageGIF
         } for
         grestore
       }
      bind def
      0 8 inter
      4 8 inter
      2 4 inter
      1 2 inter
    }
    {	/Width Width   /Height Height
        /DataSource D
      >> imageGIF
    }
   ifelse
   saved end end end restore
 } bind def

% This lets you do stuff on the command line like:
% gs -sDEVICE=pdfwrite -o stuff%03d.pdf viewgif.ps -c "(image.gif) << /PageSize 2 index viewGIFgetsize 2 array astore  >> setpagedevice viewGIF"
% so the output size is influenced by the original image.
/viewGIFgetsize		% <file|string> ==> [width height]
{
   save 20 dict begin
   /saved exch def
   dup type /stringtype eq { (r) file } if
   /F exch def
   F readGIFheader /Header exch def
     currentdict Header end begin begin
   VGIFDEBUG { Header { exch == == } forall (----------------\n) print flush } if
   F readGIFimageHeader /ImageHeader exch def
     currentdict ImageHeader end begin begin
   F 0 setfileposition		% reset file pointer
   Width Height
   saved end end end restore
} bind def

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