Film Negative Invert and Processing in L* Gamma FAQ

Discussion in 'Digital Darkroom' started by dmitry_shijan, Mar 23, 2021.

  1. digitaldog

    digitaldog Andrew Rodney

    Yes, it has such a potential (what's the gamut of the scene, the film used etc?). And a color target who's gamut is sufficiently large enough a container to define an input profile to get to a large RGB Working Space gamut.

    The ProPhoto RGB color space, also known as ROMM RGB (Reference Output Medium Metric), is an output referred RGB color space developed by Kodak. It offers an especially large gamut designed for use with photographic output in mind. The ProPhoto RGB color space encompasses over 90% of possible surface colors in the CIE L*a*b* color space, and 100% of likely occurring real-world surface colors documented by Pointer in 1980,[3][4] making ProPhoto even larger than the Wide-gamut RGB color space. The ProPhoto RGB primaries were also chosen in order to minimize hue rotations associated with non-linear tone scale operations. One of the downsides to this color space is that approximately 13% of the representable colors are imaginary colors that do not exist and are not visible colors.
    ProPhoto RGB color space - Wikipedia

    Usually or never? You understand, there's no reason to guess and no harm using a container for a color space that is KNOWN to be large enough. Hence, ProPhoto RGB.
  2. digitaldog

    digitaldog Andrew Rodney

    If you guys want to enter into a technical discussion, let's get the technical stuff correctly defined, OK?
    Sorry, if the TRC isn't 1.8, it's not ProPhoto RGB. A Working Space has primaries, white point and TRC/Gamma that define them exactly. IF the gamma isn't 1.8, it isn't ProPhoto RGB. You can build a Working Space with ProPhoto RGB primaries and a different TRC or Gamma than 1.8 and call it "Dmitry RGB" if you wish but it's not ProPhoto RGB.
    No. Melissa RGB is the color space used in Lightroom for the Histogram (NOT processing) that uses ProPhoto RGB primaries and a 2.2 TRC like sRGB. It's called Melissa RGB BECAUSE the TRC isn't a 1.8 gamma. Or that would define ProPhoto RGB. Melissa RGB isn't used anywhere expect in the Histogram in Develop module without a soft proof. The underlying color space used for processing (again, ProPhoto RGB primaries and WP but 1.0 TRC) has no name.
    All explained decades ago: Management in Lightroom.pdf
  3. Then somebody needs to tell the writer of the Wikipedia ProphotoRGB page.
    Screen shot from Wikipedia.
  4. digitaldog

    digitaldog Andrew Rodney

    Sorry, RIMM (got that "i" wrong):
  5. This is really useful info.
    By the way, i just compared those "flat" exported files processed in Lightroom/ACR with Process Version 2003 or 2010 and with all adjustments turned off, and they still look not the same "flat" as real "flat" untouched exports from other raw editors.
    So probably that scene-referred image export may be the only technically correct way to go for Lightroom/ACR film scan exports.
    Overall i don't use Lightroom/ACR, so i may not understand it as pure as i understand other tools.
  6. Ooops. Missed a vital part off that screenshot.
  7. digitaldog

    digitaldog Andrew Rodney

    Are you now suggesting ProPhoto RGB doesn't have a gamma 1.8 encoding by design?
    And do tell the person who believes the color space is named "ProphotoRGB". Both are wrong concepts.

    Go to a color scientist and see the facts:
    Welcome to Bruce Lindbloom's Web Site
    Note: The gamma of sRGB is not exactly 2.2, but rather, is a grafting together of two different functions, that when viewed together, may be approximated by a simple 2.2 gamma curve. When using a simple gamma function, Photoshop calls this "Simplified sRGB." All calculators, spreadsheets and reference tables found on my entire site use the proper functions, not the simplified versions. The proper sRGB functions may be found here and here.
    The gamma curve of ProPhoto RGB is 1.8. No extraneous discussions, just the spec's for a lot of RGB Working Spaces based on actual color science, by color scientists like Bruce.
    And the basics of gamma and linearity:
    Last edited: Apr 22, 2021
  8. digitaldog

    digitaldog Andrew Rodney

    And there's no reason why they should.
    We are in violent agreement. ;)
  9. I read deeper, and seems workflow described in that article is rather useless today. It was designed for Photoshop CS3 (2007) so it assume ACR use Process Version 2003 or 2010. Also as i remember in those days ACR was able to export only to sRGB, AdobeRGB and ProPhotoRGB profiles. So they create that "hack" to convert in Photoshop exported image form ProPhotoRGB gamma 1.8 back to ProPhotoRGB gamma 1.0.
    Current versions of ACR can export directly to any installed ICC profile, so you can just switch to Process Version 2003 or 2010, reset all adjustments to 0 and export to custom-made ICC profile. For example to "native" scene-referred ProPhotoRGB gamma 1.0 or to ProPhotoRGB L*gamma if it required by your workflow.

    To be honest all those Lightroom/ACR hacks are very depressive and i can't see any point to use it when there are a lot of other apps that can do proper "flat" scene-referred export in way more simpler and user friendly way.
    It is real mystery why it is so complicated for Adobe simply add option in ACR to remove build-in contrast curve same as other raw editors normally can do:
  10. digitaldog

    digitaldog Andrew Rodney

    That assumption is wrong**. Those who desire scene referred rendering don't find setting ACR for scene referred useless today. NOTHING whatsoever has changed with respect to this since CS3.
    Next question.
    To be honest, that's rubbish. Again, some users want to produce scene referred rendering and that's why both Adobe and the ICC have provided a way to do so. IF you don't wish to follow that, fine.
    I completely understand and accept after all these pages, when the discussion comes to ACR/LR/producing scene referred rendering or not, this is all a real mystery to you.
    Next question. Or in terms of resetting curve points in ACR/LR; RTFM :p

    **“Most of our assumptions have outlived their uselessness“.
    -Marshall McLuhan

    Last edited: Apr 23, 2021
  11. From
    - "The linear_RIMM-RGB_v4.icc profile contains a linear CCTF. It should be used when a linear scene-referred encoding is desired, but only with 16 (or more) bits per channel."
    - "Open the raw file in ACR. Note that the color rendering controls should be left at zero or linear in order to produce a scene-referred image."
    - "Set the Workflow Options Space to ProPhoto RGB and the Depth to 16 Bits/Channel."
    - "Open the converted (to scene-referred) raw file into Photoshop"
    -"Edit -> Convert to Profile and CONVERT to the linear_RIMM-RGB_v4.icc profile using the relative colorimetric rendering intent."

    As for me this is all looks the same as simple export to custom-made ProPhoto RGB with Linear gamma ICC profile directly from ACR :)
  12. Also seems every raw processor use some unique detection and trimming of "empty" data range in debayered raw file. So the same "flat" scene-referred export from different raw processors usually have slightly different brightness.
  13. digitaldog

    digitaldog Andrew Rodney

    It isn't. They don't look the same, I could calculate the exact deltaE difference of all three and, I only know of one that has specific means to export Scene Referred rendering (although I also own Iridient Developer).
    Trimming empty data range?
    Every raw converter is akin to your color negs; they differ based on a slew of factors. You're just NOW figuring out this fact or Trimming empty data range is another assumption?
    This is what raw looks like:


    The rest is created uniquely in each raw converter.
  14. digitaldog

    digitaldog Andrew Rodney

    Found how how yet? There's at least 3 ways to do this IF you know how.....
  15. I don't know how to name that correctly. But looking how it works in PhotoLine i assume that there is always some sort of reserved empty space in debayered source image. And it is usually trimmed under the hood. PhotoLine operates with imported raw file at very low level so you can see some things the that is impossible to see in other apps.

    For example, here is how processed raw file looks when you open it in PhotoLine.

    Now we can turn off that auto generated contrast curve:

    And next we can go even deeper and bring back all trimmed empty data. This is totally useless empty data, so i guess other raw converters usually autodetect and trim it by default somehow.
  16. I know how unprocessed RAW file looks, PhotoLine also can show image in raw pattern mode like this. And in reality those black and white pixels. They are usually shown as RGB pattern only for more human friendly preview:
    Last edited: Apr 23, 2021
  17. digitaldog

    digitaldog Andrew Rodney

    If you know what you say you know, you would know that this isn't front page news and never was:
    The rest is created uniquely in each raw converter.
    What you don't appear to know or can explain despite being asked is:

    Say what?

    BTW, the terminology you're looking for is demosaicing (also de-mosaicing, demosaicking or debayering).
    Demosaicing - Wikipedia
    Last edited: Apr 23, 2021
  18. digitaldog

    digitaldog Andrew Rodney

    So you made up a word for an attribute you can't explain?
    Yes, you assume. Please get facts then post**.
    Assumption or factual data point you can prove?
    Do tell us how many other raw converters, exactly the names of each app you compared this to, to come up with the assumptive text:
    ....impossible to see in other apps.
    Yes, you're guessing again. Assuming, making up terms etc. It's getting pointless to continue because this is a photo, color, technical discussion, not a fiction fictional discussion based on assumptions.
    Meanwhile, your time may be better spent learning how to reset curves in ACR unless you never care to use it which is fine with me.
    **"Get your facts first, then you can distort them as you please." --Mark Twain
  19. What is correct terminology for this "empty space" in debayered image :) ?
  20. I don't use ACR/Lightroom and never will be, so i have no any interest to fit it to this workflow and search how to reset curves in it. I already post gif animation with possible option here Film Negative Invert and Processing in L* Gamma FAQ
    If you know how to do it please provide info or links that may be useful for other people.

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