[tlug] Any graphics experts here?

[Brian Chandler <brian@example.com>]

I am trying to print some sheet music using an online printing service 
(laser A3 output, stapled in a proper "book"); I assembled a PDF file 
containing the 12 pages and sent it, to receive an error message 
complaining that it is not 'greyscale'...

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■1色刷り面がグレースケールで作成されておりません。
　お手数ですがグレースケールに変換していただき、再入稿いただくか、
　ご注文内容をフルカラーに変更していただく必要がございます。

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Well, of course in "reality" (if such exists) there are only black and 
white bits, and I don't know much about PDF, but all that should be 
necessary to change is for any colour value to be moved to its closest 
(by any standard) point on the r=b=g line. I have given a 
("black-n-white") PDF file to our local printers for a poster, and they 
have no difficulty at all in printing it in black and white.

All searches seem to lead to Imagemagick, which isn't really the job, 
because it does everything by resampling, resulting in terrible quality. 
But even so, it is not clear what it means for a pdf to be 
"grayscale"... see following thread:

http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=16175

This says that even if you convert the colorspace value in the PDF to 
"gray(scale)", you will see sRGB given as the "colorspace", because 
Imagemagick always creates 3D colour. Worse, I found authoritative 
comments suggesting that in fact *objects* within a PDF have 
colorspaces, but the PDF file itself does not. So I don't really see how 
I could even tell if their printing system is going to believe it is a 
monochrome file anyway. FWIW, here are the "help" pages, which 
presumably might do something if I were using either of these bits of 
software:
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グレースケール変換のポイントは下記URLをご参照下さい。
【Illustratorで変換の場合】
http://www.graphic.jp/technical/check_ai/req04.php
【Photoshopで変換の場合】
http://www.graphic.jp/technical/check_psd/req03.php
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Sorry, this is a bit rambling. I don't quite where to go next...
Brian Chandler