Keep black ink from printing

[jensgerbitz@yahoo.ca]

Hi there,

I recently came across an interesting effect - by accident - while printing on my Epson 7900. The image (night shot of Dresden), didn't have photo black due to a bad clog, but LK and LLK printed fine.

I cancelled the job after about 30% of the image was printed to take care of the clog. After defeating it I printed the image as it should have been printed the first time around, but realized that I actually really like the first attempt with the missing K.

So the question is: how can I selectively keep only the photo K channel from printing? (I'm using Lightroom 4.4).

Thanks,
Jens

[Mark D Segal]

I doubt very much this is doable. But you could simulate the effect by how you edit the photo in Photoshop or Lightroom or whatever you are using.

[luxborealis]

Any chance of us seeing the effect? A side-by-side scan or photo?

BTW bubble gum would work! 

[GrahamBy]

I'm guessing it was a solarization effect?

For a B&W image you could try manipulating the transfer curve: if you pull it completely up to the top left corner, then bring it back down to near the diagonal at around 15-20%, that might be a starting point.

Trying to do it for colour would be, umm, challenging.

[Mark D Segal]

What is a transfer curve? - never heard of such a thing. Do you mean the tone curve?

[disneytoy]

Sounds like solarization effect.

[GrahamBy]

What is a transfer curve? - never heard of such a thing. Do you mean the tone curve?

Yes, the tone curve. AKA characteristic curve. It defines the transfer function from input to output.

Transfer function is also the standard term for the mapping to a screen display, when the definition of gamma. Transfer function, characteristic curve, "tone curve" are all the same concept, and transfer function is the generic description of the mapping from input to output just about any transducer or filter, viz MTF (in Fourier space).

Oh, google just found me yet another one: "Tone Transfer Function"
http://www.digitizationguidelines.gov/term.php?term=tonetransferfunctionttf

[Mark D Segal]

Thanks for confirming. The usual and accepted term in the digital imaging community is "Tone Curve" and what it does is commonly referred to as "remapping", in the sense of remapping tones from darker to lighter and vice-versa. That's why I was a bit confused about the fancy lingo. Reminds me of "giclee" printing for what we do with our Epson P800s etc. :-). Anyhow, it's clear now.

[krismaz]

One option would be to edit the K curve in the profile, but for that you need some profile editing software (EFI profile editor, or xrite equivalent). Technically, printer will use K ink from about 95% to 100% black density, everything below is printed using LK or LLK. I know that is the case for Canon IPF printer so assume Epson implementation will be similar. You could edit the image so that it never goes above 95% on K channel. Unfortunately that will mean converting to cmyk, which might introduce colour shifts or limit your gammut (depending on the image). 

[donbga]

Thanks for confirming. The usual and accepted term in the digital imaging community is "Tone Curve" and what it does is commonly referred to as "remapping", in the sense of remapping tones from darker to lighter and vice-versa. That's why I was a bit confused about the fancy lingo. Reminds me of "giclee" printing for what we do with our Epson P800s etc. :-). Anyhow, it's clear now.

The Transfer Function phrase or name has been used for years by enthusiasts producing digital negatives to linearize alternative process prints. As someone mentioned it maps an input value to a new output value using an ACV curve. Yes a Tone Curve - no fancy lingo really.

[luxborealis]

I 'm out of my league here (hence the gum comment  , but what about converting the file to a CMYK colour space then reducing the "C" channel to match what you were getting from only the LLK and LK inks.

[Jeremy Roussak]

I 'm out of my league here (hence the gum comment  , but what about converting the file to a CMYK colour space then reducing the "C" channel to match what you were getting from only the LLK and LK inks.

The "C"? Or the "K"?

Jeremy

[luxborealis]

The "C"? Or the "K"?

Jeremy

The K! The K! Thanks Jeremy!

[jensgerbitz@yahoo.ca]

Holy cats guys,

Thanks for the voluminous answers! This is the first time I've checked this thread since posting. I have to put myself in the same camp as luxborealis in feeling like a lot of this is above my pay grade and that bubblegum may be my best solution 

I'll take a closer look at what my options are later this evening. It may be a day or two before I report back with some results, but fwiw, yes, I think that this might be best described as something similar to the solarization effect.

Cheers,
Jens