Type 3 fonts conversion - pdf

Question

I am parsing Type3 glyphs fonts from Pdf to postscript. The input file have inline image with data streams flate decode filter applied.the filter has predictor 15.
Any body can help how I take the image streams form pdf to postscript.
This is how the input stream is given in pdf
32 0 obj
<<
/Length 342
>>
stream
37 0 4 -52 33 -1 d1
0.01 0 0 0.01 0 0 concat
gsave 2900 0 0 -5100 400 -100 concat
BI
/IM true
/W 29
/H 51
/BPC 1
/D[1
0]
/F/Fl
/DP<</Predictor 15
/Columns 29>>
ID xœ=Ì¡
Â`ÅñÿeÂLθ n`0>Ù`ñ
f[¦DŒF_ÁhC1ì%Ä)¶o.¢Ÿ"†ßá†s®àì]^ÏŠÅS³tFËÂÚ3sç'Æi èÐÇ:j‹¹¨åìOTÿ ª•ÉÙÕÅŸ¨‡¹Ó$°ÆΚWèÁ!¯Cê
÷0&f µtðV ©Ë÷iôíتÄ~Ø•Œöí&´« +ro#Ê‚ûÏÅùlßG'
EI gRestore
endstream
endobj
And here is what i am trying to write in output in Postscript
/g21 {
37 0 4 -52 33 -1 setcachedevice
q
[0.01 0 0 0.01 0 0] concat
q
[2900 0 0 -5100 400 -100] concat
[ xœ…ѱNÃ0à3©p'l` ¢abä*‰'#‚W`KP¡00öQ`d# ¨CWž€u`‰štj4Ü]# /ù¤œíÿ| ÂìÊüå7úŠ‰V'‚ª¦zò¡9à*´º
m1Õ`ñ—íü‹­‡½Gù#ãÝAVxc¥Ž®"6oFܬJHÃB3(æod¾…xFP†o$!v±Ã»·0—gØY÷J$û„`´#zÊ
Oí¼œÑ¸é`Ê}ü…ñ.Z¯›cF4\¡*O¤ÑPÒYòî¦/éG‘qÑç¼2>öq<Üœ<
B˜5‚²¢ºÎ/èqUTUàoÓ9͔Π܉ä²z ‡S×ÛÙC(PA²š7è­T¾ŽCGÈRaLéåksnˆÃ0z<zø:ž=
]
0
<<
/ImageType 1
/Width 29
/Height 51
/ImageMatrix [29 0 0 -51 0 51]
/BitsPerComponent 1
/Decode [1 0]
/DataSource { 2 copy get exch 1 add exch }
<</Predictor 15
/Columns 29
>>
/FlateDecode filter
>>
imagemask
pop pop
gRestore
gRestore
} def

Answer 1

PostScript has mostly the same filters as PDF. You don't need to decompress the data, just use the FlateDecode filter in PostScript and leave the compressed data untouched.
Note you'll need Language Level 3 for Predictor 15 (or any other PNG predictor) but that shouldn't be a problem, level 3 has been the standard for 18 years.
Otherwise you'll need to implement a version of the FlateDecode filter which supports the PNG Predictor. I believe zlib is quite capable of this.
[EDIT]
Your 'PostScript output' is incomplete, you are using PDF operators (q and Q) which you have not provided a definition for. Apart from anything else this makes it impossible to run the code through an interpreter. Kindly supply a complete simple example file, as requested. Not pasted code, I'm not inclined to go and create a file myself, and besides, binary doesn't cut and paste at all well.
Off the top of my head from desk checking I can't immediately see a problem, but since I can't run the code, I could easily be missing something.
[EDIT 2]
And that file, unsurprisingly, works fine.
You haven't supplied the PostScript file that you are creating. Its rather hard for me to tell what's wrong with the PostScript you created by looking at the PDF file you started with.
You could, of course, use Ghostscript (and I see you've used it to create the PDF file) to create a PostScript file, and then look at what that contains. If you set -dCompressFonts=false then the output font won't even be compressed.
For example:
37 0 4 -52 33 -1 d1
0.01 0 0 0.01 0 0 cm
q 2900 0 0 -5100 400 -99.9998 cm
BI
/IM true
/W 29
/H 51
/BPC 1
/D[1
0]
/F[/A85
/CCF]
/DP[null
<</K -1
/Columns 29>>]
ID
-D=,M5m+t^0_>op8\HM"Du]KKrr2rthqG/5qU_ik]$f$TlUslD91qoN93j0%dckk:ld^*DV25!+
!WX>~>
EI Q
Of course you'll need to look at the prolog to see how all the procedures used there are defined, but you can do that yourself, you certainly don't need me to do it. Notice that the imagemask uses the CCITTFax and ASCII85 decode filters, its trivial to add additional filters. Since the data is guaranteed to be 'monochrome' (its a mask) the CCITT filter generally gives superior compression to Flate.
Note that if you are really using Ghostscript 9.05 then you should upgrade, that is 6 years old.
It might possibly help if you were to explain why you want to take an ugly, bitmapped, type 3 font from PDF and make an ugly, bitmapped type 3 PostScript font from it.
[EDIT 3]
well looking at your PostScript file, the definition of the glyphs does not match what you've put in your question. The actual content looks like this:
/g10135{
88 0 4 -70 82 8 setcachedevice
q
[
0.01 0 0 0.01 0 0 ] M
q
[7800 0 0 -7800 400 800 ]M
<<
/ImageType 1
/Width 78
/Height 78
/ImageMatrix [ 78 0 0 -78 0 78]
/BitsPerComponent 1
/Decode [1
0]
/DataSource ....binary data.....
<< /Predictor 15
/Columns 78
/BitsPerComponent 1>>
/FlateDecode filter def
>> imagemask
Q
Q
}bind def
You have not supplied either a file, procedure or string source as a value for the DataSource key in the dictionary. Essentially, the PostScript interpreter reads and tokenises the /DataSource key, and then proceeds to process the binary as PostScript. Unsurprisingly this causes an error 'syntaxerror in (binary token, type=156)' when processed with Ghostscript.
If you had got past that then you would have discovered that the filter operator takes a data source as well and you haven't supplied one for that either.
So you need to create a data source for your binary data. Up to you how you do that but currentfile is one way. Or readstring given that you know the string length.
So something like:
<<
/ImageType 1
/Width 29
/Height 51
/ImageMatrix [29 0 0 -51 0 51]
/BitsPerComponent 1
/Decode [1 0]
/DataSource
<length> string dup
currentfile exch readstring
.....binary data.....
<<
/Predictor 15
/Columns 29
>> /FlateDecode filter
>> imagemask
Obviously you'll have to fill in yourself by knowing the string length. The dictionary argument to FlateDecode looks to me like it shouldn't be needed.
[Edit 4]
I notice that this is appears to be intended for commercial use. Nothing wrong with that, but I'm not going to do all your homework for you, if its your job its up to you to learn the language well enough to do the job.
I'm skipping lightly over the actual implementation details below in an attempt to outline where you are going wrong. In practice things are a little more complex, I haven't discussed how the procedure stored in the CharStrings dictionary is created, or the difference with early name binding (which is an important concept in PostScript).
Your existing code is:
/g10135{
88 0 4 -70 82 8 setcachedevice
q
[
0.01 0 0 0.01 0 0 ] M
q
[7800 0 0 -7800 400 800 ]M
<<
/ImageType 1
/Width 78
/Height 78
/ImageMatrix [ 78 0 0 -78 0 78]
/BitsPerComponent 1
/Decode [1
0]
/DataSource {417 string dup
currentfile exch readstring}
...binary data....
<< /Predictor 15
/Columns 78
>>/FlateDecode filter def
>> imagemask
Q
Q
}bind def
So, the PostScript interpreter reads those bytes one at a time, and converts them into tokens. This either results in an executable token, which is executed, or an operation on one of the stacks.
So /g10135 is terminated by the { character, because that's a reserved character. The / introduces a name object, so we end up with the name object g10135 which we push on to the operand stack. The { character introduces an executable array so we put a mark on the operand stack.
Next we read 88, terminated by a white space character. That's a numeric so we store that on the operand stack, likewise the other numbers. The operand stack now contains:
/g10135
mark
88
0
4
-70
82
8
We then read setcachedevice, which is terminated by a white space. That isn't a standard token so the interpreter starts looking through the dictionaries on the dictionary stack, looking for a definition. Since it is a standard operator, we find it in systemdict and execute it. That consumes 6 operands from the operand stack, it has no other effects (actually it does, but this is a bit special because we are executing inside a font, but we'll ignore that for now).
Next we encounter a q, again this is looked up in every dictionary on the dictionary stack to find a definition. This is defined in your own prolog as a gsave, so it takes no operands and returns no operands, it simply saves the graphics state, incrementing the save depth by 1.
I'm not going to go through the rest it would be tedious, however, eventually we reach your /DataSource, this is a name, so we push it on the operand stack. The next thing we encounter is a { that's a procedure definition so we push a mark on the operand stack. We then encounter a 417 so we push that, string, dup, currentfile, exch and readstring, so our stack looks like:
/DataSource
mark
417
string
dup
currentfile
exch
readstring
Then we get the character } That is the closing mark for an executable array, so we create the array and push it onto the operand stack:
/DataSource
{....}
Then we return to the procedure and continue executing it. The next thing we find is some binary data so we try to execute that as PostScript binary tokens. Because it isn't valid the interpreter throws an error.
Just creating an executable array is not sufficient to actually execute it. If you look at the outline code I posted at the end of edit 3 above you will note that I did not put the readstring and so on in an executable array, I simply allowed the interpreter to execute that code immediately.
By doing so the readstring acts on currentfile (the actual PostScript program in this case) and reads bytes of data from the current point in that file. The current point will be immediately after consuming the white space which terminates the readstring, ie the actual binary data. The readstring operator reads enough bytes from the file to fill the string, leaving the string on the operand stack. The file pointer has moved on to the byte after the binary data, and the interpreter resumes token scanning at that point. So it then creates the FilterParams dictionary puts the /FlateDecode name on the stack and then executes the filter operator which consumes the name, the dictionary and the string operands, returning a file object. That file object then becomes the value associated with the DataSource key in the image dictionary which is passed to the imagemask operator.
While I haven't tested that code, its basically correct. There are of course other ways to achieve the same aim.
That's basically about as far as I'm prepared to go with this, you need to go and look at what I've written and compare it with your own program.
Note that the simplest way to investigate this is to take the contents of the CharProc (excluding the setcachedevice) and just run that as a PostScript program.