Using Ghostscript in server mode to convert PDFs to PNGs - ghostscript

Question

while i am able to convert a specific page of a PDF to a PNG like so:
gs \
-dSAFER \
-dBATCH \
-dNOPAUSE \
-sDEVICE=png16m \
-dGraphicsAlphaBits=4 \
-sOutputFile=gymnastics-20.png \
-dFirstPage=20 \
-dLastPage=20 \
gymnastics.pdf
i am wondering if i can somehow use ghostscript's JOBSERVER mode to process several conversions without having to incur the cost of starting up ghostscript each time.
from: http://pages.cs.wisc.edu/~ghost/doc/svn/Use.htm
-dJOBSERVER
Define \004 (^D) to start a new encapsulated job used for compatibility with Adobe PS Interpreters that ordinarily run under a job server. The -dNOOUTERSAVE switch is ignored if -dJOBSERVER is specified since job servers always execute the input PostScript under a save level, although the exitserver operator can be used to escape from the encapsulated job and execute as if the -dNOOUTERSAVE was specified.
This also requires that the input be from stdin, otherwise an error will result (Error: /invalidrestore in --restore--).
Example usage is:
gs ... -dJOBSERVER - < inputfile.ps
-or-
cat inputfile.ps | gs ... -dJOBSERVER -
Note: The ^D does not result in an end-of-file action on stdin as it may on some PostScript printers that rely on TBCP (Tagged Binary Communication Protocol) to cause an out-of-band ^D to signal EOF in a stream input data. This means that direct file actions on stdin such as flushfile and closefile will affect processing of data beyond the ^D in the stream.
the idea is to run ghostscript in-process. the script would receive a request for a particular page of a pdf and would use ghostscript to generate the specified image. i'd rather not start up a new ghostscript process every time.

Answer 1

So why can't you simply use a command like this:
gs \
-sDEVICE=png16m \
-dGraphicsAlphaBits=4 \
-o pngimages_%03d.png \
\
-dFirstPage=20 \
-dLastPage=20 \
gymnastics.pdf
\
-dFirstPage=3 \
-dLastPage=3 \
sports.pdf
\
-dFirstPage=33 \
-dLastPage=33 \
athletics.pdf
\
-dFirstPage=4 \
-dLastPage=4 \
lazyness.pdf
This will generate several PNG images from different PDFs in a single go.