Re-defining the Digital Negative
Negative made by the editing programs
TruNeg logarithmic negative
Carbon print from TruNeg logarithmic negative
The fact is that the negatives produced by editing programs are unusable, but instead of investigating why they don’t work and finding a solution, an entire industry of videos, websites, and sometimes confusing advice has developed on how to fix the problem.
The cause of this problem is the fundamental difference between digital and analogue prints. Analogue alternative process prints respond according to the logarithmic H&D DLogE curve and require logarithmic negatives; editing programs use linear colour scales and percentages, and creating logarithmic negatives with RGB or Lab colour scales obtained from a spectrophotometer is like trying to fit a square peg into a round hole.
This conflict can be resolved using logarithms, as the negative and positive logarithms of the digital image are inversely proportional. This means that a 16-bit analogue digital negative covering the entire range of tones from the deepest shadow to the brightest highlight can be calculated with a Python-based data-processing program at the press of a button, completely eliminating the need for densitometers, scanners, linearization procedures, etc.
TruNeg manages the various alternative processes by creating profiles. They map the difference between the calculated negative and the negative that produces a good print made by using test strips and the interactive curve window.
Profiles can be accessed for free on the TruNeg website for Argyrotype, Carbon/Gum Bichromate (A. Dich.), Classic Cyanotype, Salt and Van Dyke Brown. A generic profile is available to assist in making profiles for unlisted processes.
The interactive 16-bit logarithmic plot generated by the program contains a grid that corresponds to each step of a logarithmic stepwedge printed with the test strip, so that changing some selected print tones by one stepwedge tone is achieved by adjusting the negative curve by one grid line, providing a simple and predictable mechanism for tweaking alternative process prints.
The Basic steps to making prints with TruNeg negatives.
ONE. Download and print the Calibration Negative and find the minimum exposure that produces a clean white and maximum density when printed on the selected process.
TWO. Open the Calibration menu and input the two RGB values that produce ”just white’ and ”just black” from the calibration print. Download and load the process profile from the website and save the Preset.
THREE. In the Convert Menu, open a test strip, select the Preset and press OK to convert to negative.
FOUR. Print the negative and print the test strip.
FIVE. Correct any unsatisfactory tones that are caused by printer and chemistry variations, and reprint the test strip with the new preset. If happy, print the print.
The green circles show where the plot has been clicked to darken the highlights of the salt test strip by one tone.