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

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

[Till Kamppeter]

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?

    Till

On 05/08/2022 22:47, Sebastian Wick wrote:
> On 2022-08-02 08:39, Till Kamppeter wrote:
>> Hi,
>>
>> we had talked about the demise of colord on the GUADEC, right after my
>> talk about the New Architecture of printing and scanning.
>>
>> You wanted to send me an e-mail, but I did not receive one.
>>
>> Could you tell me more about soft proofing and which free software
>> tools are used for that?
>>
>>    Till
> 
> Hey,
> 
> nice to hear from you. Got sick after GUADEC and then was really busy so 
> sorry for the delay.
> 
> If you want to try out a soft-proofing workflow I would suggest to use 
> GIMP. Grab for example a DCI P3 profile 
> (https://www.color.org/chardata/rgb/DCIP3.xalter), your display profile 
> (GNOME auto-generates one for your display and puts it in 
> ~/.local/share/icc/) and a printer ICC profile if you have one (or an 
> sRGB profile if you don't https://www.color.org/chardata/rgb/srgb.xalter).
> 
> You can find the relevant settings in: Preferences -> Color Management.
> 
> Make sure "Image display mode" is "Color-managed display". For the 
> "Color Managed Display -> Monitor profile" choose your display profile. 
> For "Soft-Proofing -> Soft-proofing profile" choose the printer profile 
> and also make sure "Mark out of gamut colors" is checked.
> 
> Create or load a new image. Go to "Image -> Color Management". Make sure 
> "Enable Color Management" is checked. Then select "Assign Color Profile" 
> and assign the build-in sRGB profile.
> 
> If you now paint something on the image with a strong color (pure green 
> for example) and then go to "Preferences -> Color Management" and change 
> "Image display mode" to "Soft-proofing" you should see some parts of 
> your image being marked as out of gamut.
> 
> The image is in sRGB but not all sRGB colors can be shown on the printer 
> and now you can see where they are. If you turn off "Mark out of gamut 
> colors" you can see the image like it would appear when it gets printed 
> (except that the printer could also show colors that your display can 
> not show, but this usually gets you pretty close).
> 
> If you plan to only print the image you could assign the printer profile 
> to the image and then soft-proofing would show you where on the image 
> you used colors that your display can not show you.
> 
> When the sRGB image is done you would then do the color space conversion 
> to the printer profile (in GIMP using "Image -> Color Management -> 
> Convert to Color Profile") with the exact settings you want.
> 
> In both cases you end up with an image in the printer color space and 
> you would not want the printer to do any more processing.
> 
> I hope that explains the usual workflow. If you have any questions 
> please ask!
> 
> Cheers,
> Sebastian

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

[Michael Sweet]

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Till,

> On Aug 22, 2022, at 4:14 AM, Till Kamppeter <till.kamppeter@gmail.com> 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


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

[Till Kamppeter]

On 22/08/2022 13:51, Michael Sweet wrote:
> 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.

[...]

> 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.

[...]

Does this mean that in a colord-free world we proceed as follows:

If the printer does not provide built-in, downloadable profiles via the 
"printer-icc-profiles" printer IPP attribute, we have to get the 
profiles separately from the manufacturer's web site (printer is not 
self-contained, not really actually "driverless" ...) and upload them to 
the printer using HTTP PUT and registering them with the 
Set-Printer-Attributes IPP operation, so that they are available for all 
users of this printer. Am I right? And, after the upload, will the newly 
uploaded profiles be listed in the "printer-icc-profiles" IPP attribute, 
so that every user knows which profiles are available?

Now, with profiles listed by the "printer-icc-profiles" printer IPP 
attribute, could the soft-proofing software simply download and use 
these profiles?

If this is the case, the IPP printer is more or less replacing colord 
for printers.

In case of a legacy printer the Printer Application should be able to 
hold color profiles, ideally both in the Snap's static file system image 
for the profiles which come with the Printer Application and in the 
variable/state file system for user-added profiles. Ideally such 
functionality should get added to PAPPL.

    Till

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

[Michael Sweet]

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Till,

> On Aug 22, 2022, at 9:04 AM, Till Kamppeter <till.kamppeter@gmail.com> wrote:
> ...
> Does this mean that in a colord-free world we proceed as follows:
> 
> If the printer does not provide built-in, downloadable profiles via the "printer-icc-profiles" printer IPP attribute, we have to get the profiles separately from the manufacturer's web site (printer is not self-contained, not really actually "driverless" ...) and upload them to the printer using HTTP PUT and registering them with the Set-Printer-Attributes IPP operation, so that they are available for all users of this printer. Am I right? And, after the upload, will the newly uploaded profiles be listed in the "printer-icc-profiles" IPP attribute, so that every user knows which profiles are available?

No.

Most printers don't host ICC profiles and don't support HTTP PUT or Set-Printer-Attributes.

You need to still have a way to associate ICC profiles with a print queue (temporary or otherwise), assuming of course you want to offer soft proofing.

> Now, with profiles listed by the "printer-icc-profiles" printer IPP attribute, could the soft-proofing software simply download and use these profiles?

For the class of printers that supports it, yes.  But I'd treat this as a source of profiles that can be downloaded on demand and associated with the local queue (alongside any profiles the user has installed manually).

> In case of a legacy printer the Printer Application should be able to hold color profiles, ideally both in the Snap's static file system image for the profiles which come with the Printer Application and in the variable/state file system for user-added profiles. Ideally such functionality should get added to PAPPL.

Right now I have no plans to add explicit support for ICC profiles to PAPPL as the class of printer being supported won't get anything out of it - *no* open source driver provides ICC profiles at this time, label and B&W laser printers won't benefit, and Gutenprint's notion of color management makes using ICC profiles basically useless - too many knobs.

(FWIW, PAPPL *does* know about ICC resource files and will assign the correct MIME media type for them, there just isn't a way to associate a profile with a Printer or the Job Template options that will select it...)

________________________
Michael Sweet


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

[Michael Sweet]

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Sebastian,

> On Aug 23, 2022, at 7:48 AM, Sebastian Wick <sebastian@sebastianwick.net> wrote:
> ...
> When you say associate a profile with a print queue, what exactly does
> that mean?

I mean "when doing a soft-proof of this document for this printer, use this profile". It could just be implemented as a history/most recently used chooser in the soft-proofing UI, where there can be a "Printer Profile" submenu/section (populated from "printer-icc-profiles") and "Other..." to pick a file from disk.

> That all images in the queue have color characteristics
> described by that profile?

No, given the current CUPS print pipeline we are best served by sticking with standard color spaces (sRGB, sGray, and AdobeRGB) and only using printer profiles for soft-proofing.  Longer term we should probably have CUPS use printer-specific profiles (as supplied by the printer) to produce DeviceK/RGB/CMYK raster data for non-PDF printers, but since the number of printers supporting that is very small we shouldn't try to optimize that case yet.

> That the printer converts the images which
> are tagged by possibly other profiles to that profile? Can you associate
> any profile with a print queue or only ones the printer supports? Do all
> printers support certain color spaces?

So IPP Everywhere and AirPrint require sRGB/sGray raster support, and most photo printers also support AdobeRGB.  A few large format (raster) printers (currently) support printer-icc-profiles, and any PDF printer will support embedded ICC source profiles that get chained with the internal ICC profiles to produce correct DeviceN color on the printer itself.

> Is this kind of information documented somewhere?

Yes, in the IPP Everywhere specification:

	https://www.pwg.org/ipp/everywhere.html

________________________
Michael Sweet


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

[Till Kamppeter]

On 23/08/2022 13:23, Michael Sweet wrote:
> 
> No.
> 
> Most printers don't host ICC profiles and don't support HTTP PUT or Set-Printer-Attributes.
>

OK, most printers are not high-end enough that one would want to do 
soft-proofing for them. Apps/filters just sending sRGB to them is good 
enough.

>> Now, with profiles listed by the "printer-icc-profiles" printer IPP attribute, could the soft-proofing software simply download and use these profiles?
> 
> For the class of printers that supports it, yes.  But I'd treat this as a source of profiles that can be downloaded on demand and associated with the local queue (alongside any profiles the user has installed manually).
> 
>> In case of a legacy printer the Printer Application should be able to hold color profiles, ideally both in the Snap's static file system image for the profiles which come with the Printer Application and in the variable/state file system for user-added profiles. Ideally such functionality should get added to PAPPL.
> 
> Right now I have no plans to add explicit support for ICC profiles to PAPPL as the class of printer being supported won't get anything out of it - *no* open source driver provides ICC profiles at this time, label and B&W laser printers won't benefit, and Gutenprint's notion of color management makes using ICC profiles basically useless - too many knobs.
> 

The current 6 Printer Applications (LPrint, hp-printer-app, the 4 
retro-fitting ones) actually do not need it, also if Gutenprint and 
HPLIP will get replaced by native ones at a certain point in time. But 
later on, a manufacturer could theoretically want to make a Printer 
Applications for high-end printers with ICC profile support ...

    Till

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

[Till Kamppeter]

On 23/08/2022 13:23, Michael Sweet wrote:
> 
> No.
> 
> Most printers don't host ICC profiles and don't support HTTP PUT or Set-Printer-Attributes.
>

OK, most printers are not high-end enough that one would want to do 
soft-proofing for them. Apps/filters just sending sRGB to them is good 
enough.

>> Now, with profiles listed by the "printer-icc-profiles" printer IPP attribute, could the soft-proofing software simply download and use these profiles?
> 
> For the class of printers that supports it, yes.  But I'd treat this as a source of profiles that can be downloaded on demand and associated with the local queue (alongside any profiles the user has installed manually).
> 
>> In case of a legacy printer the Printer Application should be able to hold color profiles, ideally both in the Snap's static file system image for the profiles which come with the Printer Application and in the variable/state file system for user-added profiles. Ideally such functionality should get added to PAPPL.
> 
> Right now I have no plans to add explicit support for ICC profiles to PAPPL as the class of printer being supported won't get anything out of it - *no* open source driver provides ICC profiles at this time, label and B&W laser printers won't benefit, and Gutenprint's notion of color management makes using ICC profiles basically useless - too many knobs.
> 

The current 6 Printer Applications (LPrint, hp-printer-app, the 4 
retro-fitting ones) actually do not need it, also if Gutenprint and 
HPLIP will get replaced by native ones at a certain point in time. But 
later on, a manufacturer could theoretically want to make a Printer 
Applications for high-end printers with ICC profile support ...

    Till

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

[Solomon Peachy]

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On Tue, Aug 23, 2022 at 07:23:18AM -0400, Michael Sweet via Printing-architecture wrote:
> Right now I have no plans to add explicit support for ICC profiles to 
> PAPPL as the class of printer being supported won't get anything out 
> of it - *no* open source driver provides ICC profiles at this time, 
> label and B&W laser printers won't benefit, and Gutenprint's notion of 
> color management makes using ICC profiles basically useless - too many 
> knobs.

FWIW, the dye-sublimation printers that Gutenprint supports nearly all 
have a manufacturer-supplied ICC profile, and putting aside the question 
of redistributibility, I would very much like to have a gutenprint-based 
printer application provide said profile to the application on demand, 
and/or automagically apply it to whatever is printed.

 - Solomon
-- 
Solomon Peachy			      pizza at shaftnet dot org (email&xmpp)
                                      @pizza:shaftnet dot org   (matrix)
Live Oak, FL                          speachy (libra.chat)

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

[Michael Sweet]

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Solomon,

> On Aug 23, 2022, at 11:20 AM, Solomon Peachy <pizza@shaftnet.org> wrote:
> 
> On Tue, Aug 23, 2022 at 07:23:18AM -0400, Michael Sweet via Printing-architecture wrote:
>> Right now I have no plans to add explicit support for ICC profiles to
>> PAPPL as the class of printer being supported won't get anything out
>> of it - *no* open source driver provides ICC profiles at this time,
>> label and B&W laser printers won't benefit, and Gutenprint's notion of
>> color management makes using ICC profiles basically useless - too many
>> knobs.
> 
> FWIW, the dye-sublimation printers that Gutenprint supports nearly all
> have a manufacturer-supplied ICC profile, and putting aside the question
> of redistributibility, I would very much like to have a gutenprint-based
> printer application provide said profile to the application on demand,
> and/or automagically apply it to whatever is printed.

Assuming that you could use/bundle the profile, I would rather see Gutenprint use it to convert sRGB or AdobeRGB to the printer's DeviceCMY color space, otherwise the number of clients that take advantage of it will be exceedingly small.

________________________
Michael Sweet


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

[Michael Sweet]

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Sebastien,

> On Aug 24, 2022, at 11:47 AM, Sebastian Wick <sebastian@sebastianwick.net> wrote:
> ...
> For input they all support sRGB, sGray. Some also support AdobeRGB, but
> how do you know when a printer supports AdobeRGB? Some support device
> profiles and they are advertised with printer-icc-profiles.

The "pwg-raster-document-types-supported" and "urf-supported" attributes advertise the supported raster color spaces. We use that to determine which cupsColorSpace values to use in the PPD file.

> Assuming I know what input profiles the printer supports, how do I tell
> the printer what profile my document is in? You already partially
> answered the question: PDF printers use the embedded ICC profiles. Do
> all the document formats support embedded profiles? Is that always how
> printers figure out the source profile of a document?

PDF supports it, PostScript somewhat less so.  For raster (image/pwg-raster and image/urf), the color space is a single well-known space (sRGB, sGray, AdobeRGB) or device color space (RGB, CMY, CMYK, K, W), for which the Client has converted all color data in the source document to the destination color space.

>>> Is this kind of information documented somewhere?
>> Yes, in the IPP Everywhere specification:
>> 	https://www.pwg.org/ipp/everywhere.html
> 
> Either I missed something, which is highly likely, or the way color
> management is supposed to work is very open to interpretation (looked at
> IPP Everywhere v1.1, and PWG 5100.13).

We are adding clarifications to the updates of these documents now, so if you can provide some specific feedback I can make sure your concerns are addressed.

________________________
Michael Sweet


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