How to convert CIELab to monitor %K ink

[FL at CC]

Hey everyone!

I'm making some curves for my digital negatives (to compensate for paper, processing, etc). I'm trying to get my head around how I can adapt CIELab readings I'm using from my Colormunki Photo measuring the silver print Dmax so I can then calculate to monitor grayscale K%. Any hints as to how I can acheive this? It's really got me stumped.

 

[Bob Carnie]

Hey everyone!

I'm making some curves for my digital negatives (to compensate for paper, processing, etc). I'm trying to get my head around how I can adapt CIELab readings I'm using from my Colormunki Photo measuring the silver print Dmax so I can then calculate to monitor grayscale K%. Any hints as to how I can acheive this? It's really got me stumped.

If you are using a Mac you can open the Colour Meter and put it to Lab settings and do you measurments.
or you can open the image up in photoshop and set the info palette to LAB and take your readings. size of aperture of eyedrop tool needs to be approximate same size I use 3 x 3

hope this helps.

 

[FL at CC]

Hi Bob - thanks indeed for the info on this, love your work no doubt!

Just one further question when generating the curve to put in after I’ve found my Dmax and taken sample readings from each increment (between 0-100), I’m still a little stumped as to what correction values I require to enter into the curve. (I do know that there should be a correction sample for each 5, 10, 15, 20, etc) but as the ink values would be inverse for the negative to the print for input/output.

 

[ced]

Use one of the automated generators out there like Peter Mrhar's EDN: http://www.photomrhar.com/download/

 

[FL at CC]

Thanks ced, this looks interesting - is using Peter Mrhar’s automated tool suitable for making negatives for silver prints (ie: not alternative process, etc such as cyanotype, etc). This method is quite foreign to me as I’ve gone down the path of taking sample measurements of a Dmax segment and basing all other gray densities for correction from there.

Is there any direct way to convert Yule density to say monitor %k or RGB? (the method I’m using is to take the Dmax of my test strip, look up the corresponding Dmax level on a Yule-Nielsen table (the Huntington Witherill method) and plot correction from the logarithmic levels as part of the Dmax the sample taken. This has been one incredible stumbling block!

 

[ced]

Shoot a line to Peter Mrhar:
http://www.photomrhar.com/about/

 

[Patrick Robert James]

It seems to me that you might be over complicating the whole thing, or getting bogged down in the technical details. If I were to make a digital neg today for silver printing I'd do it the same way I'd make a neg for any other process. Start by figuring out what density inks correspond to the max and min you can get, then build a curve. Pretty simple really.

I don't use any of the ways on the internet. I just built a matrix in LAB from 0 to 100 then printed it out. Get your readings, or eyeball it, then adjust and print another. If that works, make a suitable curve. I do everything in LAB.

I made silver prints from digital negs 18 years ago. Hard to believe it has been that long. Dang.... Actually now that I'm thinking about it I made digital negs for platinum prints back in '97. I am starting to feel old now....

 

[FL at CC]

Thanks everyone for the very kind help thus far! I'm really bogged down at the moment with making the negatives that I've been going around in circles for days... I'm not that skilled or savvy on making the profiles - for me at the moment I'm just trying to find a cohesive process that I can follow that uses the QTR RIP to control the inks and for linearization. I'm using my Colormunki to take the readings and have saved the 21-step patch samples into a .csv file. Is anyone able to point me into the direction of how to convert the sampled .csv file and linearize it?