View Full Version : Predicting color balance and print exposure times.

Stephen Willard
26-Apr-2005, 09:15
I have an idea for precisely predicting color balance and print exposure times for color negative papers. I am looking for your considerations.

First, let me provide you with the circumstances. I am a fine art landscape photographer. To maintain quality control and consistency from print to print, I make a master copy of each image I have. I use the master copy as a target when printing subsequent prints. I have found that making precise copies of the master print to be very difficult if not impossible without wasting lots of paper and time. I can do a better job by making test prints than I can with a color analyzer, however both still fall short of my goal.

My overall strategy is to apply the analysis at the print level rather than at the negative level as color analyzers do. This should eliminate all variables attributed to paper batch and processing. I will be using a print densitometer for taking readings which far more accurate than a color analyzer. So here is my grand plan.

1. I will “rough in” a test print that is close to the master print using the manual test strip method. I can get close in two sheets of paper.

2. I will then select a critical area on the Master print and take a RGB reflective density reading and a white light reflective density reading. I will then repeat this procedure on the test print in the same spot.

3. The differences in the white light density readings will tell me the time change that I need to apply to the test print to achieve the same density as the master print. I have already done this using a linear interpolation and found that this method to be very accurate provide the prints are reasonably close in density.

4. The difference in RGB readings will tell me the color head changes I need to make and the times changes I need to make as a result of changing the filtration. These times will be added to the white light time noted above.

Clearly, I will have to quantify the impact of unit changes in print density for both white light and RGB readings would have on the color head and final print times. Once I have done this, then I can develop an equation which inputs all the densities and computes time changes and color head changes needed to generate a print that matches the master print with a greater degree of accuracy and much less paper and time.

So does this seem possible? Has any body done something similar to this?

Mark Sampson
26-Apr-2005, 10:28
Yes, I've been involved with projects that have been controlled in similar fashion. The method is a lot of work, and may not be much quicker than printing by eye, if your tolerances are extremely tight. Something worth thinking about is the consistency of your print processor. RA-4 is a forgiving process but needs to have a lot of paper run through it to avoid process changes. You'll want to run a control strip every day, and your densitometer will need to be calibrated regularly, as well. And of course use the same batch of paper (although the current papers are more consisitent than in the EP-2 days).