Ghostscript postscript pswrite is encoding text - matlab

Question

Why is Ghostscript pswrite encoding my text in its output? Consider the following MWE:
%!PS-Adobe-3.0
%%Title: mwe.ps
%%Pages: 001
%%BoundingBox: 0 0 595 842
%%EndComments
%%Page: 1 1
%%PageBoundingBox: 0 0 595 842
0 0 1 setrgbcolor
0 0 595 842 rectfill
1 0 0 setrgbcolor
247 371 100 100 rectfill
/Times-Roman findfont
72 scalefont
setfont
newpath
247 300 moveto
(Chris) show
showpage
Saving this MWE to file and viewing in GSview will display a blue page with red square and my name underneath. Now run this file through Ghostscript 9.06 with the following command line:
"c:\Program Files\gs\gs9.06\bin\gswin64c.exe" ^
-dSAFER -dBATCH -dNOPAUSE ^
-sDEVICE=pswrite -sPAPERSIZE=a4 -r72 -sOutputFile=mwe_gs.ps mwe.ps
See Ghostscript output below. Can someone please explain what is happening here. Whilst the two rectfill commands are still apparent, my text (Chris) has been encoded and is no longer distinguishable.
Is there an alternative postscript device which would retain my text please?
<snip>
%%Page: 1 1
%%PageBoundingBox: 0 0 595 842
%%BeginPageSetup
GS_pswrite_2_0_1001 begin
595 842 /a4 setpagesize
/pagesave save store 197 dict begin
1 1 scale
%%EndPageSetup
gsave mark
255 0 r6
0 0 595 842 rf
255 0 r3
247 371 100 100 rf
Q q
0 0 595 0 0 842 ^ Y
255 0 r3
249 299 43 50 /5D
$C
,6CW56m1G"ZORNkWR*rB:!c2;9rlWTH="2^^[(q"h>cG<omZ2l^=qC[XbO:8_[?kji-8^"N#3q*
jhL~>
,
289 300 41 49 /0P
$C
4r?0p$m<EkK3,0>s8W-!s8W-!s8W,u]<1irI=*p=<t0>_#<)>Is8K6,aTi'$~>
,
325 300 30 33 /5I
$C
49S"pc4+Rhs8W-!s8W)oqdD:saRZq[4+k%):]~>
,
349 300 24 49 /0T
$C
4q%Ms%;PqCs8W-!s8W%1_qkn/K?*sYFSGd:5Q~>
,
377 299 23 34 /5M
$C
-TQR7$&O'!K+D:XribR9;$mr4#sqUi.T#,dX=Y&Llg+F`d^HC#%$"]~>
,
cleartomark end end pagesave restore
showpage
%%PageTrailer
%%Trailer
%%Pages: 1
%%EOF
NOTE: This might seem an odd activity but I'm exploring the idea of using Ghostscript to 'clean up' postscript output from Matlab application..

Answer 1

The 'text' has been converted to images, not vector paths. This is a serious limitation of the pswrite device, and one of the reasons it is deprecated, you should use the ps2write device instead. The only reason the pswrite device is still included at all is for epswrite which uses it (which is why the pswrite and epswrite output looks the same). At some point there will be an eps2write device and pswrite will be binned.
ps2write output is, by default, compressed. If you want uncompressed output, use the -dCompressPages=false switch on the command line.
If all you want is the location of the text you might consider the txtwrite device. The default implementation of this creates a plain text representation of the input, but you can have it output a faked up XML instead which includes things like the origin of the text.

Answer 2

Here is a simple example of the show operator being redefined to display position information about the show, along with performing the standard show operation. With ghostscript you can run multiple files, so the header file would be a prefix to the other file, which alters standard behavior.
The redefined show could have included font name and size. The data could have been written to a disk file, rather than dumped to the console. Any of other operator could have also been redefined, like rectfill, fill, stroke... Because the original operator is also called, you can convert a .ps to .pdf using a pdfwrite device, while at the same time obtaining position information.
gswin32c.exe -dBATCH -dNOPAUSE header.ps trash.ps
gswin32c.exe -sDEVICE=pdfwrite -dCompressPages=false -sOutputFile=test.pdf header.ps trash.ps
output
currentpoint x:247.0 y:300.0 pathbbox 249.015,298.992 400.066,349.184 text:Chris currentrgbcolor:1.0,0.0,0.0( )
currentpoint x:50.0 y:90.0 pathbbox 50.8682,89.2852 181.327,139.184 text:Fred currentrgbcolor:1.0,0.0,0.0( )
currentpoint x:150.0 y:200.0 pathbbox 150.867,184.298 304.154,247.673 text:Mary currentrgbcolor:1.0,0.0,0.0( )
currentpoint x:300.0 y:350.0 pathbbox 300.867,348.993 598.79,398.681 text:Mr. Green currentrgbcolor:0.0,1.0,0.0( )
currentpoint x:100.0 y:400.0 pathbbox 100.866,399.202 358.547,449.183 text:Mr. Blue currentrgbcolor:0.0,0.0,1.0( )
Header.ps
/mydict 5 dict def
mydict begin
/show
{
(currentpoint ) print
currentpoint exch 10 string cvs ( x:) print print 10 string cvs ( y:) print print
gsave dup false charpath flattenpath
( pathbbox ) print
pathbbox
4 -1 roll 10 string cvs print (,) print
3 -1 roll 10 string cvs print ( ) print
2 -1 roll 10 string cvs print (,) print
10 string cvs print ( ) print
grestore
( text:) 10 string cvs print
dup print ( ) print
( currentrgbcolor:) print
currentrgbcolor
3 -1 roll 10 string cvs print (,) print
2 -1 roll 10 string cvs print (,) print
10 string cvs print ( ) ==
systemdict /show get exec
} def
trash.ps
%!PS-Adobe-3.0
%%Title: mwe.ps
%%Pages: 001
%%BoundingBox: 0 0 595 842
%%EndComments
%%Page: 1 1
%%PageBoundingBox: 0 0 595 842
0 0 1 setrgbcolor
0 0 595 842 rectfill
1 0 0 setrgbcolor
247 371 100 100 rectfill
/Times-Roman findfont
72 scalefont
setfont
newpath
247 300 moveto (Chris) show
50 90 moveto (Fred) show
150 200 moveto (Mary) show
0 1 0 setrgbcolor
300 350 moveto (Mr. Green) show
0 0 1 setrgbcolor
100 400 moveto (Mr. Blue) show
showpage

Answer 3

The text has been converted to vector paths. 249 299 43 50 /5D begins the first letter "C", then 289 300 is the "h", 289 300 the "r"....
What pswrite has done is eliminate the need for a font, so while your original code used /Times-Roman, the distilled code doesn't need any font, but rather draws the text using vectors.
I'm not sure exactly what you are after, but you could try "ps2write" or "epswrite" as alternatives to "pswrite". pswrite is used to write to ps level 1 standard and ps2write will write ps level 2 output. Nobody requires ps level 1 anymore, so level 2 would be acceptable. The epswrite will write to encapsulated postscript (eps).