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Postscript to PDF Conversion Without Losing Font Quality

In this section I will try to explain in detail how to solve a very common problem to researchers who want to distribute papers electronically: how to convert a postscript file to Adobe PDF format without losing font quality?

First, make sure you know what postscript and PDF format are, if you don't, then you probably won't be interested in any case.

Second, let's suppose you do know what these formats stand for and are interested to know how to convert ps to pdf format, the next question is: do you know why sometimes the conversion quality is so bad in terms of the appearance of fonts?

The answer is in the format of the fonts. To make things simple, I will not try to be technical and only talk about the most obvious here: Fonts, like everything else you see and print, are basically graphic shapes. There are two major types of fonts. Bitmap and Vector. Bitmap fonts, also called Type 3 fonts, store every single font as essentially an image, pixel by pixel, point by point, and as you know, if you actually resize an image, it won't look as good as its original size. The problem can be somewhat reduced by techniques like Antialiasing, but it won't be completely solved. Vector fonts, also called Type 1 fonts, on the other hand, store every font in a drawing language, so instead of storing the image, it stores the coordinates of the border points and the direction to draw a line. In other words, it stores information like "draw a point in location (1, 3), and draw a line from it, at an angle of 27 degree, with a length of 2 inches, ..." It's obvious that when you resize the font, you just resize all the length variable in the font description using the same scale, and you will still get good quality.

And the reason why some of the converted-from-postscript PDF files look bad, is because the original postscript file uses Type 3 bitmap fonts. To get a better PDF output, you need to regenerate the postscript file using Type 1 fonts.

To achieve that, you must have the original LaTeX source file, or the DVI file, to start with. Otherwise it can NOT be fixed! (well, it can, using an utility program called, you guessed it, FixFont, but it is NOT guaranteed to have a fix) The second thing is to have a correct LaTeX installation and configuration, meaning type1 fonts must be correctly installed and configured to use by DVIPS---this step is certainly not trivial, for teTeX and MikTeX type 1 fonts are installed with the distribution, for other TeX distribution you might have to install them manually. To configure DVIPS to use type 1fonts, you must modify the file for DVIPS, usually in /texmf/dvips/config directory, you must add in the correct lines to tell DVIPS to use the correct fontmap file. Another solution is to use the "-Ppdf -G0" option when you evoke DVIPS, this option tells DVIPS to use the pseudo PDF printer to generate postscript files.

Sometimes you would have to delete the current LaTeX font cache in order to see the change, otherwise you should use the -M switch in running DVIPS. The "-M" option turns off automatically font generation.

You can find most of the related information in the web, if you searched and couldn't find them, or are just too lazy to do the search, you can always email me for the detailed solution.