Densitometer readings to photoshop k values

Erik L · Oct 20, 2015

Hi folks, I'm trying to make a curve for digital negs using the instructions in C. andersons book. I'm not trusting my scanners reading of the printed out step tablet (PD, kallitype, carbon emulsions tested) and would like to verify the results with my reflection densitometer. Is there a way I can convert my densitometer readings into the percent readings that are needed to make a correction curve in Photoshop? Or better yet, does anyone have any relatively foolproof correction curves for arches platine for PD and kallitype they would be willing to share? I'm a novice at the digi neg thing! My printer is the epson p600. I think qtr is beyond my comprehension at this point. Any help is greatly appreciated! Thanks

calebarchie · Oct 20, 2015

Apparently this can do it, if you can deal with the 21-step wedge. I have asked the same question in this thread.

http://www.dpug.org/forums/f8/qtr-correction-curve-tool-inkjet-prints-negatives-3877/

Erik L · Oct 20, 2015

Thanks, that thread went right over my head[emoji1]
I guess what I want to know is if there is a math formula to convert densitometer reading to the 0-100% reading that photoshop uses? I'm so new at this it all seems Greek to me.

calebarchie · Oct 20, 2015

I wish to know the same too. Here is an Except from Rosenbergs process document.

IV. Calibration Curves by Reflectance Densitometer.
It is also possible to perform the calibration process using a reflectance densitometer, such as
the X-Rite 811. Reflectance density can be converted to monitor %K by use of the YuleNielsen
equation. I feel this affords a more accurate method of calculating a correction
curve. But this will be covered more fully in a future update.

There was no future update, but you can go from there and research it. I believe Nelsons PDN method has this information, but I do not wish to spend the money on the book right now.
Alternatively, you can attempt to extract the equation from the provided exel tool.

calebarchie · Oct 20, 2015

I have found this archived article from Nelson of PDN -
http://www.viewcamera.com/freetrial/dig negs.pdf

"X-Rite Corporation
has a handy little
program called ToolCrib,
which allows
you to input readings
from a reflection
densitometer directly
into software applications
— very
handy, and it is free!"

Don't need to pay $75 to know that hah! I am going to check it out.

pschwart · Oct 20, 2015

Here is all you need, See B&W Calibration System for Digital Output:

Dead Link Removed

calebarchie · Oct 20, 2015

pschwart said:
Here is all you need, See B&W Calibration System for Digital Output:

Dead Link Removed

Super! Since I don't actually have an X-rite.
I found references to Witherill in the DPUG archive, he seemed to know how to do it, I didn't find his site though!

pschwart · Oct 20, 2015

calebarchie said:
Super! Since I don't actually have an X-rite.
I found references to Witherill in the DPUG archive, he seemed to know how to do it, I didn't find his site though!

You don't need an X-Rite -- any reflection densitometer will do.

calebarchie · Oct 20, 2015

I was referring to using the X-rite tool (which seems to support generic devices also). But in this case I have a portable densitometer.

Erik L · Oct 20, 2015

Thanks guys! That Witherill link looks like it'll do the trick if I am interpreting it right

RalphLambrecht · Oct 22, 2015

Erik said:
Hi folks, I'm trying to make a curve for digital negs using the instructions in C. andersons book. I'm not trusting my scanners reading of the printed out step tablet (PD, kallitype, carbon emulsions tested) and would like to verify the results with my reflection densitometer. Is there a way I can convert my densitometer readings into the percent readings that are needed to make a correction curve in Photoshop? Or better yet, does anyone have any relatively foolproof correction curves for arches platine for PD and kallitype they would be willing to share? I'm a novice at the digi neg thing! My printer is the epson p600. I think qtr is beyond my comprehension at this point. Any help is greatly appreciated! Thanks

some of the answer is subjective but attached is my take on this;Sorry can't upload the file;send me an email to rlambrec@ymail.com and I'll send you what you need1Oh, now it worked;have un with it

Erik L · Oct 22, 2015

Thanks Ralph

RalphLambrecht · Oct 23, 2015

Erik said:
Thanks Ralph

I hope it was what you wanted or needed;if not, let me know

Richard Boutwell · Nov 17, 2015

Erik said:
Thanks, that thread went right over my head[emoji1]
I guess what I want to know is if there is a math formula to convert densitometer reading to the 0-100% reading that photoshop uses? I'm so new at this it all seems Greek to me.

This process is a pretty complex one. You first need to convert Density to the CIEXYZ color space and then convert that to CIELAB (you really only need the XYZ_Y to get to LAB_L though) then you can use that as the K% that QTR will use.

The spreadsheet template I made and linked to in that thread has those density conversion calculations built into it. If you Really want to read some Greek check out this post: Dead Link Removed

Sent from my iPhone using Tapatalk

RalphLambrecht · Nov 18, 2015

Erik said:
Thanks, that thread went right over my head[emoji1]
I guess what I want to know is if there is a math formula to convert densitometer reading to the 0-100% reading that photoshop uses? I'm so new at this it all seems Greek to me.

Yes, there is but Greek is simple in comparison

Densitometer readings to photoshop k values

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