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+%! viewjpeg.ps Copyright (C) 1994 Thomas Merz <tm@pdflib.com>
+%
+% This program is free software; you can redistribute it and/or modify it
+% under the terms of the GNU General Public License as published by the
+% Free Software Foundation; either version 2 of the License, or (at your
+% option) any later version.
+%
+% This program is distributed in the hope that it will be useful, but
+% WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+% Public License for more details.
+%
+% You should have received a copy of the GNU General Public License along
+% with this program; if not, write to the Free Software Foundation, Inc.,
+% 59 Temple Place, Suite 330, Boston, MA, 02111-1307.
+
+% $Id: viewjpeg.ps,v 1.1.6.2.2.1 2003/04/12 14:02:39 giles Exp $
+% View JPEG files with Ghostscript
+%
+% This PostScript code relies on level 2 features.
+%
+% Only JPEG baseline, extended sequential, and progressive files
+% are supported. Note that Adobe PostScript level 2 does not include
+% progressive-JPEG support. Ghostscript with IJG JPEG v6 or later
+% will decode progressive JPEG, but only if you edit gsjmorec.h to
+% enable that feature.
+%
+% Updated by L. Peter Deutsch 20-May-1997:
+% move the usage example to the beginning
+% Updates by Tom Lane 6-Sep-1995
+
+% Usage example:
+% (jpeg-6/testimg.jpg) viewJPEG
+
+/languagelevel where {pop languagelevel 2 lt}{true} ifelse {
+ (JPEG needs PostScript Level 2!\n) print flush stop
+} if
+
+/JPEGdict 20 dict def
+JPEGdict begin
+
+/NoParamMarkers [ % JPEG markers without additional parameters
+ 16#D0 16#D1 16#D2 16#D3 16#D4 16#D5 16#D6 16#D7 16#D8 16#01
+] def
+
+/NotSupportedMarkers [ % JPEG markers not supported by PostScript level 2
+ 16#C3 16#C5 16#C6 16#C7 16#C8 16#C9 16#CA 16#CB 16#CD 16#CE 16#CF
+] def
+
+% Names of color spaces
+/ColorSpaceNames << /1 /DeviceGray /3 /DeviceRGB /4 /DeviceCMYK >> def
+
+% read one byte from file F
+% - ==> int --or-- stop context
+/NextByte {
+ F read not { (Read error in ViewJPEG!\n) print flush stop } if
+} bind def
+
+/SkipSegment { % read two bytes and skip that much data
+ NextByte 8 bitshift NextByte add 2 sub { NextByte pop } repeat
+} bind def
+
+% read width, height, and # of components from JPEG markers
+% and store in dict
+/readJPEGmarkers { % - ==> dict --or-- stop context
+ 5 dict begin
+
+ { % loop: read JPEG marker segments until we find SOFn marker or EOF
+ NextByte
+ 16#FF eq { % found marker
+ /markertype NextByte def
+ % Is it S0F0=baseline, SOF1=extended sequential, SOF2=progressive ?
+ markertype dup 16#C0 ge exch 16#C2 le and {
+ NextByte pop NextByte pop % segment length
+ % Ghostscript and Adobe PS accept only data precision 8
+ NextByte 8 ne {
+ (Error: not 8 bits per component!\n) print flush stop
+ } if
+
+ % Read crucial image parameters
+ /height NextByte 8 bitshift NextByte add def
+ /width NextByte 8 bitshift NextByte add def
+ /colors NextByte def
+
+ DEBUG { currentdict { exch == == } forall flush } if
+ exit
+ } if
+
+ % detect several segment types which are not compatible with PS
+ NotSupportedMarkers {
+ markertype eq {
+ (Marker ) print markertype ==
+ (not supported!\n) print flush stop
+ } if
+ } forall
+
+ % Skip segment if marker has parameters associated with it
+ true NoParamMarkers { markertype eq {pop false exit} if } forall
+ { SkipSegment } if
+ } if
+ } loop
+
+ currentdict dup /markertype undef
+ end
+} bind def
+
+end % JPEGdict
+
+% read image parameters from JPEG file and display the image
+/viewJPEG { % <file|string> ==> -
+ save
+ JPEGdict begin
+ /saved exch def
+ /scratch 1 string def
+ dup type /stringtype eq { (r) file } if
+ /F exch def
+
+ readJPEGmarkers begin
+ F 0 setfileposition % reset file pointer
+
+ % We use the whole clipping area for the image (at least in one dimension)
+ gsave clippath pathbbox grestore
+ /ury exch def /urx exch def
+ /lly exch def /llx exch def
+
+ llx lly translate
+ width height scale
+
+ % use whole width or height, whichever is appropriate
+ urx llx sub width div ury lly sub height div
+ 2 copy gt { exch } if pop % min
+ dup scale
+ ColorSpaceNames colors scratch cvs get setcolorspace
+
+ % prepare image dictionary
+ << /ImageType 1
+ /Width width
+ /Height height
+ /ImageMatrix [ width 0 0 height neg 0 height ]
+ /BitsPerComponent 8
+ % If 4-component (CMYK), assume data is inverted per Adobe Photoshop
+ colors 4 eq {
+ /Decode [ colors { 1 0 } repeat ]
+ } {
+ /Decode [ colors { 0 1 } repeat ]
+ } ifelse
+ /DataSource F /DCTDecode filter
+ >> image
+
+ end % image parameter dictionary
+
+ saved end restore
+} bind def