Forcing Ghostscript to use antialiasing when converting a PDF to PNG?

Question

I'm using GPL Ghostscript 9.07 (2013-02-14) on OS X (10.8.4) to convert many PDFs to PNGs.

It works fine except for one of the PDFs which turns into a PNG with jagged edges. In other words, Ghostscript turns off antialiasing for that particular PDF for some reason.

The PDF in question.

The output:

In other cases it works fine (sample: pdf -> png).

I use this command:

gs -dNOPAUSE -dBATCH -dPDFFitPage -sDEVICE=pngalpha -g200x150 -sOutputFile=01.png 01.pdf

Is it possible to force Ghostscript to use antialiasing for that PDF?

Any tips are appreciated.

Answer 1

This worked for me:

gs -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 -sDEVICE=jpeg -dTextAlphaBits=4 -dGraphicsAlphaBits=4 -r150  -sOutputFile=foo-%d.jpg foo.pdf

Source: ImageMagick convert pdf to jpeg has poor text quality after upgrading ImageMagick version to 6.7.8

The above would work for a JPG; for PNG, replace the -sDEVICE option with your choice, example: -sDEVICE=png16m

Source: http://ghostscript.com/doc/current/Devices.htm

Answer 2

You can try -dGraphicsAlphaBits= with values 1,2 or 4 which may or may not make a difference. It made some improvement for me, but its a small graphic at low resolution with an awkward curve, so not so much as might be expected.

Or you can use one of the anti-aliasing devices (eg tiffscaled) which are more flexible. There is no anti-aliased device for PNG output but it would be trivial to convert TIFF to PNG.

By the way, your PDF file specifically turns off anti-aliasing on the components:

8 0 obj
<</AntiAlias false/ColorSpace/DeviceCMYK/Coords[0.0 0.0 1.0 0.0]/Domain[0.0 1.0]/Extend[true true]/Function 10 0 R/ShadingType 2>>

You might like to try and see what happens if you change AntiAlias to true, though I doubt this will have an effect as I'm pretty sure the aniti-aliasing is applied to the internal rendering of the shading, not the edgses.