Re: [Printing-architecture] Bye-Bye colord - OR - Poll ICC profiles via IPP for soft proofing

Michael Sweet <[email protected]> Mon, 22 Aug 2022 07:51:37 -0400
Newsgroups	dev.linux.lists.printing-architecture
Message-ID	<[email protected]>
Till,

> On Aug 22, 2022, at 4:14 AM, Till Kamppeter <[email protected]> wrote:
> 
> Hi Sebastian,
> 
> thank you for your explanations on how to do soft proofing and sorry for the late reply.
> 
> Hi Michael, Ira, ...
> 
> is there any way to poll the printer's ICC profile(s) from the printer via IPP ? Or is it not needed as all IPP printers are required to receive their data in sGray/sRGB/AdobeRGB and then convert to the printer's inks/toners internally? Would soft proofing still make sense in such a case? If yes, with which profile?
> 
> Would it still make sense to soft-proof and also to color-correct for higher-end printing also if the printer is driverless IPP? Or is driverless IPP generally avoided for higher-end printing?

So you are asking two different questions...

Color Profiles
--------------

While IPP Everywhere and AirPrint printers will always support standard color spaces, high end photo/fine art printers will also support device color spaces (typically RGB or CMYK) which are described by the color profiles reported by the "printer-icc-profiles" attribute.  For AirPrint printers printers are also required to support uploading new profiles to a printer via HTTP PUT and registering them with the Set-Printer-Attributes IPP operation so that any client on the network will be able to access the same profiles served by the printer.

The ICC profiles reported by "printer-icc-profiles" are also used for soft-proofing, although because more printers don't report their own ICC profiles (because they don't support device color spaces) this is far less likely to be available.  In this case, there is no meaningful way to do soft-proofing (a generic CMYK profile won't really be useful) but conceptually you could download profiles from a vendor's web site to do it.

The upcoming update to PWG 5100.13 adds a new set of ICC profiles that simulate how "print-color-mode" values affect the output - this is specifically targeted at soft-proofing (even for standard color spaces) and could potentially be more widely implemented.  But you can expect that this will take some time to trickle out to shipping printers over the next 3-10 years.

Finally, there will always be a need to use custom ICC profiles that the user supplies/downloads. If you are going to bother supporting soft-proofing then there should be a way to use them as well.


Drivers for High-End Printers
-----------------------------

The notion that IPP can't be used for high-end printing is utter bullshit.  IPP has been used for all kinds of printing from day one, but until 2010 (AirPrint) it was best supported on high-end printers.

In the case of things like EPSON's large format printers, they spend a fortune on one small group of color scientists inside EPSON to develop custom modules for converting sRGB to DeviceN, and these modules are now part of the printer firmware.  I spent years trying to convince them they could do this with ICC profiles while dramatically reducing the size and maintenance costs of their drivers/firmware, but universally their response was "can't be done, impossible!" even when I demoed doing it for a brand new EPSON printer in an afternoon.  Even "custom" ICC profiles for different kinds of ink or media are RGB profiles that treat sRGB as the device color space for these printers.

You can still send DeviceN bitmaps (for the subset of printers that still support ESC/p2) to support custom ink sets and media, but the market for that is small (less than 1% of all users) and is best supported by a printer application rather than wiring all of those controls directly into the print dialog.

________________________
Michael Sweet
signature.asc (application/pgp-signature, 833 B)