Home-darkroom silver-gelatin prints from digital images

Started Apr 24, 2016 | Discussions thread
OP tim baker Forum Member • Posts: 79
Re: Controlling non-linearities when going from digital to wet print

technoid:

Here's a sketch of the process. It seems complicated, but it only has to be done once, and it allows prints having richness and precision of tone exceeding the best possible with film/enlarger prints:
If starting from a color digital image, convert to b/w via your favorite method.
With Photoshop "curves" or similar, adjust the b/w image to your taste--make a best possible image, to your eyes.
Then "invert" the image, creating a screen negative.
To calibrate your particular monitor, enlarger, exposure and development process:
At a chosen f-stop, do an exposure test strip to determine exposure time needed to barely reach paper-black, the darkest the paper can be.
In "curves" raise the foot of the curve/line some amount (try 1/4 of the way up to start) and make a test print at that position, using your just-determined exposure time--use a full-scale image, with pure whites and blacks, and almost pure blacks and whites.
If near blacks go pure black on the test print, reduce exposure time a touch until almost-blacks stay almost black.
Examine the test print and see if the almost whites are too dark or too white. Adjust the foot of the curve a bit, to darken or lighten the whites tones as needed, such that almost-whites stay almost white. Two or three such adjustment tests will precisely nail the perfect foot position.
You can then use that position and exposure time for essentially all future prints when using that paper, developer, and f-stop.
Mid tones will likely be too dark at this point. Lower the center of the curve until mid tones print as they should. A print from this settings will look about perfect, pure whites, near whites, pure black and near blacks as they should be.
But mid whites and mid darks may rush too steeply or rise too slowly toward each extreme/have too much or too little local contrast. Adding an S shape to the curve, like the sensitivity curve of film, will let you precisely effect the tone distribution of your idealized screen positive image. A few trial and error test prints will be needed. That resulting S curve shape will be the generic curve you'll use for almost all of your future prints. You can make minor departures of S shape to adjust local contrasts for particular images if desired, control that not even Ansel Adams could achieve. Message me with your email address and I'll send example drawings of curves.

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Tim Baker

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