Why is there BPC but no WPC?

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    Topic: Why is there BPC but no WPC? Read 1685 Times
  • Mark D Segal
    Mark D Segal
    Silver Member
    Posts: 668
    Why is there BPC but no WPC?
    on: September 12, 2022 at 9:26 am

    Yes, your pen-ultimate reply did indeed disappear – that is weird. Anyhow I think you get the idea, and you are welcome. As a final suggestion, I recommend that you “waste” a few sheets of paper experimenting with these settings (i.e. making prints) to see exactly what they do. It will be most apparent if you use a matte paper and select a photo that has shadow detail in the L*2 to L*16 of the luminance range.

    Mark D Segal Author: "Scanning Workflows with SilverFast 8, SilverFast HDR, Adobe Photoshop Lightroom and Adobe Photoshop". Please check the PhotoPXL Store for availability.

    Sean Anderson
    Sean Anderson
    Participant
    Posts: 9
    Re: Why is there BPC but no WPC?
    Reply #1 on: September 16, 2022 at 1:57 am

    I thought I would link this white paper in case a reader might be interested. The math is over my head but it helped clarify a few things.

    https://www.color.org/WP40-Black_Point_Compensation_2010-07-27.pdf

    1. All rendering intents map the source black point to the destination black point. This is true whether Black Point Compensation (BPC) is turned on or off.

    2. All rendering intents map the source white point to the destination white point. So there is no need for a separate WPC button.

    3. BPC is a modification and improvement to the Relative intent formula. Without BPC, The Relative rendering intent causes too much shadow detail to be lost. This is why the BPC box should always be checked when using Relative.

    4. BPC has little to no effect on the Perceptual and Saturation intents. BPC does not work with Absolute nor should it.

    5. Now if Adobe had only built the BPC inside the Relative algorithm, there would be no need for a separate BPC button and life would be simpler. But I’m sure there’s a reason why they were separated. I just don’t know what that might be.

    Andrew Rodney
    Andrew Rodney
    Participant
    Posts: 294
    Re: Why is there BPC but no WPC?
    Reply #2 on: September 16, 2022 at 5:50 am

    Life is simple!

    There seems to be some perverse human characteristic that likes to make easy things difficult.” -Warren Buffett

    Keep the darn checkbox on and go forward! It either fixes a rare issue in some problem profiles or does nothing because they map black correctly.

    Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

    Sean Anderson
    Sean Anderson
    Participant
    Posts: 9
    Re: Why is there BPC but no WPC?
    Reply #3 on: September 18, 2022 at 5:29 am

     

    My shrink tells me that all the time 🤪

    In your book on page 97 it states that checking the Simulate Black Ink box turns off Black Point Compensation. But the next paragraph states that selecting the Black Ink check box turns on Black Point Compensation. I’m confused (and dazed). Do you mean that when Simulate Paper Color and Simulate Black Ink are both check, then BPC is turned off; but when only Simulate Black Ink is selected, then BPC is turned on?  Please clarify. Thanks.

    BPC

    Andrew Rodney
    Andrew Rodney
    Participant
    Posts: 294
    Re: Why is there BPC but no WPC?
    Reply #4 on: September 18, 2022 at 9:23 am

    BPC again is SOURCE to DESTINATION! Soft Proofing is a different destination.

    Read the page again. Consider what black on a display represents and ink back represents. Ditto for white.

    The key to understanding this is also the word “compensation”.

     

    Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

    Jeff Schewe
    Jeff Schewe
    Gold Member
    Posts: 109
    Re: Why is there BPC but no WPC?
    Reply #5 on: September 23, 2022 at 1:13 am

    So, here’s the real reason that Adobe included a BPC in the Adobe Ace CMM…because Thomas Knoll thought the ICC should have included black point mapping but didn’t.

    White point mapping is already included in the standard ICC CMM…

    I think Andrew knows this I know Bruce Fraser did…that’s who told me and Thomas confirmed it to me.

    • This reply was modified 2 months, 1 week ago by Jeff Schewe.
    Sean Anderson
    Sean Anderson
    Participant
    Posts: 9
    Re: Why is there BPC but no WPC?
    Reply #6 on: September 24, 2022 at 9:13 am

    So BPC is a patch job then.

    patch-job

    Mark D Segal
    Mark D Segal
    Silver Member
    Posts: 668
    Re: Why is there BPC but no WPC?
    Reply #7 on: September 24, 2022 at 9:49 am

    I don’t know what that comment contributes to the discussion. But look at this way: I recall dealing with BPC two decades back. You’d think over a period of 20 years if the ICC saw fit to include this mapping in their profile spec they’ve had ample opportunity to do so, insofar as over this period of time the ICC has made other changes to their printer profile protocols. But they didn’t. Must be a reason – whether it’s technical or bureaucratic inertia who knows, but honestly, who cares, it is is what it is and what we have works. In fact having the option to turn it on or off can periodically contribute to some artistic purpose or another. Thanks to Thomas Knoll for once again coming to the rescue way back then.

    Mark D Segal Author: "Scanning Workflows with SilverFast 8, SilverFast HDR, Adobe Photoshop Lightroom and Adobe Photoshop". Please check the PhotoPXL Store for availability.

    Andrew Rodney
    Andrew Rodney
    Participant
    Posts: 294
    Re: Why is there BPC but no WPC?
    Reply #8 on: September 24, 2022 at 12:42 pm

    The ICC doesn’t control or dictate how a CMM operates; they vary, and not all are created equally. This is why Photoshop allows us to switch among them (although doing so may not be in your best interest). ACE has BPC, and the ICC is clear on how it works and why and their recommendations:

    https://www.color.org/WP40-Black_Point_Compensation_2010-07-27.pdf

    9. Recommendations

    In the light of these considerations, the following recommendations appear reasonable for the use of BPC in ICC systems. These systems are of several different types and are intended for different users. For instance, ICC color management can be embedded in the hardware of a printing system serving
    a community of naive users, or it can be provided in an interactive environment for the use of highly 
    expert practitioners. Only the designers of these systems can make the actual choices, but here are some things for them to bear in mind:

    • BPC makes an important contribution to the ICC workflow and can be implemented with minimal change to existing color architectures. It adds value that many users have come to depend on, particularly for Relative Colorimetric RI, which has little value without BPC. This is particularly important for proofing.
    • It should be available for Perceptual and Saturation RIs as well, since it can correct problems presented by certain atypical profiles and is otherwise harmless.
    • In non-interactive environments, where the user has no direct control over this option, BPC should be activated by default. Even in interactive environments, it may be appropriate to activate BPC by default, depending on the sophistication of the intended user community.

    Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)

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