Digital Contrast Index Curve Functions

The contrast index curves for this procedure have to do with digital manipulation of the negative in preparation for printing. There is what might be said to be reciprocal methods for that procedure in the digital form. Probably the best known purveyor of this procedure is Dan Burkholder, whom I have brought up before, as well as a Peter Hrhar writing "Salt Print" a very good book on silver printing. So, why am I adding my stupid two cents to the party. Because I have another way of doing things.

When you have developed enough negatives using different developers, then plotted the densities as a CI curve, the relationship between the shape of the curve and density range becomes distinct, and clear. And the reason I bring this up is I believe there needs to be a clarification to the procedure of increasing the density range of a negative, digitally. I have named two very good photographic methods for this procedure through two different photographers. Both methods are procedurally very similar, both beginning with the positive of the image. I do not do this.

The procedures as proscribed by the two forgoing photographers works. Using Photoshop, it begins with the positive image, and using the 'Curves' function, snapping on the straight line at regular points to simulate tonal range points, then raising them above the straight line of the curve, thereby increasing the densities along that line respectively. Then, reversing that image into a negative, thereby reversing the newly arrived at density curve. The basic final step is adding a color layer to the image and applying the most suitable color to retard UV light, selected from a color matrix print test demonstrating which color in a 100 (mixed) color matrix. Turns out, for platinum/palladium (ergo silver) green is the magic color. That (forest green) color is then overlaid the image, flattened and saved. That constitutes the digital print negative.

That procedure works, of course. But the shape of that curve also influences how that finished print will look, as a density range. To best demonstrate this, another lame chart makes it a bit easier.

The top graph represents the above method of increasing densities along the curve. That graph would be equal to the graph shown in their material. Notice that the top density of that curve doesn't move, isn't increased in proportion to the other densities. To compensate for this, the green color layer is added, retarding overall print time, increasing dMax and theoretically making for a longer print range. When looking at the finished images, the range is very close to being full, ranging from absolute black to crisp white. This is not a barb on their printing skills or methodology, as both stand up to scrutiny.

Speaking for myself, I am more comfortable working with the negative than the positive. I also can read CI curves and know where that will lead when printing. Being I am really crappy dealing with digital tools, and reciprocal outcomes, I work hard to keep it simple. My method is reverse of the first example. I reverse the image from positive to negative before beginning. I do not use the Curves function. It doesn't do what I want it to, which is shifting the straight line, as it is, straight leftwards, towards increased density, proportionally. Being I have yet to figure that out, I simply do it by hand, via inspection. Kind of reminds me of Bret Weston developing over 800 8"x10" negatives that Edward sent home from Europe one summer, through visual inspection. Wow.

My method is simple, yet not one that fits well with a standard measurable function built in. If I had a functioning densitometer, digital or otherwise I could make that happen. For now, it remains a more personal artistic expression method. My method uses Lightroom 4, which may leave out a lot of photographers that do not have this software, although anyone with current access to Photoshop also has access to Lightroom, now residing in the Cloud.

I use the four control slides of Lightroom; Highlights, Shadows, Whites, Blacks, in that order as seen in the program. What I am looking for are those areas of the negative that I want prominent. I set the blacks first, eyeing those thin areas of the negative that represent black, then moving the slide until those areas, representing roughly Zone 1-2, making sure those densities are thin, then moving to the middle tones using the 'Shadows' slide, bringing up the the shadow details (same as first method) then I move on to 'Highlights' which affects the overall density of the image, and finally the 'Whites' and I bring up those densities until they are nearly opaque to the eye.

As bizarre as that seems, it also works. The difference between the two procedures is moving Zone 7-8 with the rest of the density ranges along the curve, not just the middle tones. What that also means is that you don't have to use a color layer for retarding UV light for increasing densities. Thus far, I have come to realize that an Epson printer can build up sufficient pigment density on a sheet of Inkpress acetate, or equivalent brand, to completely block UV light sufficiently to render that tonal range to remain blank white after the rest of the print is fully printed in, even when printed in direct sunlight, facing the sun.

Print tests have proven out that reaching full density range on a digital negatives does not need added spectral density. What it does require is moving the entire contrast index curve upwards, if one is looking at the Curves line. Matching that density range with the print time/intensity is the critical issue.