Digital Negative Curves

Discussion in 'Talk About Techniques' started by Ian-Barber, Oct 30, 2018.

  1. Ian-Barber

    Ian-Barber Admin Staff Member Registered User

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    Ive been spending some time experimenting with digital negatives contact printing with some very good results.
    I quickly realised that it's not a one correction curve process, each type of paper and even batch of paper can have different tonal responses.

    What I discovered was that although we send 100% black to the transfer film, by the time its gone through the darkroom process, we never actually wound up with 100% which is not surprising when you think about it. Even digital papers have their own characteristics.

    What was needed was a method whereby we could in effect map the output from the inkjet printer to the output from the darkroom paper so I decided to work with an 11 patch step wedge for the mapping.

    To help speed up the process, I decided to write a Photoshop action but this soon became awkward so I then decided to write a Javascript plugin and wrap the code behind a user interface. In theory, because this is Javascript it should work in Photoshop from around CS4 upwards.

    main-interface.jpg

    Processes:
    I only print using the Silver Gelatin process and have no means of testing it with any other processes.

    There is more information and a quick video on my website

    https://www.digitalblackandwhite.co.uk/digital-negative-curves.html
     
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  2. Ian Grant

    Ian Grant Active Member Registered User

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    QTR (Quad Tone Rip) uses different ICC profiles to produce negatives for specific processes, a negative for Silver Gelatin printing isn't suitable for say Platinum Palladium printing. In addition negatives are optimised in terms of the colour inks/pigments used to give the best exposures with UV light, so for Platinum Palladium that' a greenish black.

    The other feature of QTR is it lays down a higher ink density than the Epson print driver which is needed to achieve the higher density range required for most alternative processes.

    Ian
     
  3. Ian-Barber

    Ian-Barber Admin Staff Member Registered User

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    Yes, I agree that other processors such as Platinum do require some form of blocking ink mask usually from the yellow which is why some tweaking of the script I made would need to be done in order to introduce this mix.

    I am not convinced that the ABW driver is not capable of producing enough density at least for the silver gelatine process and the tests I have done have been very pleasing when setting the default tone option to darkest in the driver.
     
  4. David M

    David M Well-Known Member Registered User

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    Presumably you could use the Cool/Warm/Sepia adjustment facility to control additional masking colours.
     
  5. Ian-Barber

    Ian-Barber Admin Staff Member Registered User

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    In the ABW driver, yes you could use the color wheel to add the masking color
     
  6. Alan9940

    Alan9940 Active Member Registered User

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    I would be careful introducing yellow because it's the most unstable of the K3 inkset. It would seem reasonable to think that the negative density could change over time. I don't know that we need to worry about keeping digital negatives for the long term, but I don't know how fast it might change...
     
  7. David M

    David M Well-Known Member Registered User

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    Epson seem to make claims of up to seventy years for prints made with their inks. Presumably a digital negative would be stored carefully in the dark and might last even longer. This seems long enough for most purposes, but I may be misinterpreting things. I didn't find data for the specific longevity of ink on film.
     
  8. martin henson

    martin henson Admin Staff Member Registered User

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    As a matter of interest Ian, how many hours work did you put in to make this, IMHO a very useful program (script) to have.
     
  9. David M

    David M Well-Known Member Registered User

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    Seconded.
     
  10. martin henson

    martin henson Admin Staff Member Registered User

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    I have been told by Ian over 100 hours work put into the whole project, all I can say is well well done that man and hope you can sell a few to help with the time involved.
     

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