GhostScript (PostScript): Printer cut- off borders when scaling down from A* to A4 - c

Question

I'm working on a "GS Wrapper" (using the 9.20 SDK) for use by an external application. There i scale down for example a A0 Sheet to A1, A2 and A3 and it works fine. (PDF to PS, then Print)
Problem: When i scale down any input format to A4, the printer cut off the borders of the content (these are technical drawings with a black border each 5mm from the sheet edge).
Is there an opportunity to scale down the A4 (to A4) again about 95% and center the image? (This should be result in a smaller base image, say the black borders are about ~10mm away from the sheet border afterwards)
I use the following parameter for scaling:
GhostArg[0] = "-dNOPAUSE";
GhostArg[1] = "-dBATCH";
GhostArg[2] = "-dSAFER";
GhostArg[3] = "-dNOPAUSE";
GhostArg[4] = "-g2480x3508";
GhostArg[5] = "-dPDFFitPage";
GhostArg[6] = "-r300x300";
GhostArg[7] = "-sDEVICE=ps2write";
GhostArg[8] = Output;
GhostArg[9] = Input;
Solution Update:
I managed to fix this problem by insert this three lines between Arg[8] and Arg[9]:
GhostArg[9] = "-c";
GhostArg[10] = "<< /BeginPage { 0.99 0.99 scale 10 10 translate } >> setpagedevice";
GhostArg[11] = "-f";
Thanks to KenS for the /BeginPage hint.

Answer 1

It sounds like your printer has a non-printable area. This is not uncommon, the paper handling needs to hold the paper while its being printed, and this can lead to some areas of the media not being printable.
If your content reaches to the edge of the media, its possible that the printer simple cannot print there, resulting in the content being cropped.
It is entirely possible to have ps2write drop the media content to a smaller size, but you can't have it (automatically) scale down and also shift the content location, because the content is fitted to the media size.
However, the FitPage mechanism doesn't look at the content, just the media size requests. So if the input requests A3 and the selected media is A4 (and fixed) then a scale factor is applied to scale the content to the required media size (and the media request for A3 is ignored).
So what you could do is leave the code you have as it is as present, but add a BeginPage or Install procedure which uses the scale operator to further reduce the size of marks on the page, and the translate operator to move the origin slightly so that the final content is centered.
Something like (example only, untested):
<<
/BeginPage {
0.95 0.95 scale
16 20 translate
}
>> setpagedevice
By the way, you do realise Ghostscript is licenced under the AGPL ?
Also, I'd very strongly recommend that you do not use the -g and -r switches, but instead simply use -dDEVICEWIDTHPOINTS and -dDEVICEHEIGHTPOINTS to alter the media size.
The -g switch works in pixels, but high level output devices (eg pdfwrite and ps2write) don't emit pixels, they write high level vector objects. However, due to differences in the PostScript and PDF graphics models, some elements do need to be rendered to images and enclosed in that fashion in the PostScript output. By setting the resolution to 300 you are fixing the resolution at which those elements (eg pages containing transparency) are rendered. I'd suggest that you don't do so, unless you are working in a very tightly controlled workflow and know the resolution of the final output.
By using the DEVICEHEIGHTPOINTS and DEVICEWIDTHPOINTS switches you can control the media size without reference to the resolution. Note that in PostScript (and PDF) 1 point = 1/72 inch.