Altering the contrast of color papers?greenspun.com : LUSENET : Large format photography : One Thread
I am a color photographer, and I am on a never ending quest to find new tools and methods that will allow me to control contrast (primarily contrast compression) for color materials. I looked to B&W as a guide for investigating new solutions. For example I have been very sucessful using contracted development (N-1, N-1.5) for color negative film to compress and darken the highlights. I have also been very successful using pre-exposures to lighten and enhance the detail in the shadows. A big frustration with color papers is that you cannot get them in different contrasts like you can b&w papers.
Recently I read about flashing color paper to darken and enhance detail to the highlights. This technique is equivalent to pre-exposure for film. For sure, I intend to start experimenting with this method. However, this got me to thinking about how I model film and paper materials. I have always viewed them as separate parts of the process for making the final print. Color paper and film were just different and had very little in common. One was done in the field and the other was done in the darkroom. Flashing has made me rethink this assumption. Suppose we were to think of film and paper as the same, that is, they both use a light sensitive emulsion except they reside on different backing material. If you think of film and paper in this manner then the next question that begs to be answered is... can I control the contrast of the paper by altering the development times in the same manner as we apply contracted and expanded development to film!! That is, we expose the paper for the highlight and then control the shadows by altering the development times of the paper (whether its color or b&w paper).
Can anyone address this thought either in theory or practice?
-- Stephen Willard (email@example.com), October 22, 1999
I work primarily in B&W and my knowledge of color papers is poor, so please bear that in mind in reading the following. To answer your question - in theory, yes but not in practice. In general, paper contrast is better not done through variations in development time. Paper emulsions typically have steeper characteristic curves than film emulsions and are thus less amenable to control through altered development time. Papers emulsions are designed to be developed to completion i.e., to the full contrast they are capable of.
Contrast control at the paper stage is actually done through different emulsions (either through different grades of paper or through incorporation of multiple emulsions on the same paper as in variable contrast papers in which case, differential response to different wavelengths of light produce different contrasts). N+ development of papers do not work, thanks to the fact that papers typically are designed to be developed for full contrast - so you will just see a progressive darkening of the print corresponding to the entire curve shifting upwards without a change in the slope of the curve. You are also sometimes likely to see a yellow stain from oxidation products of the developer. N- development of papers is also problematic. Typically, overexposed and underdeveloped prints have a muddy appearance and weak blacks. Very often, they will be mottled due to uneven development (a risk one runs with very short development times with films as well). The controls are also less reliable given the shorter development times of papers (you doubtless have seen the grossly overexposed print flash up in seconds in the developer). I've only had one picture of mine where I liked the overexposure and underdevelopment look (and I suspect even that was merely a novelty and certainly achievable through better means such as planning a high key negative etc). Finally, the ability to produce a repeatable effect is vanishingly small.
Tricks like preflashing of the paper do not aim to alter the contrast of the paper. They merely bring the paper upto the speed point so that even the very little light coming through the highlight areas of the negative are sufficient to just produce a tone in the paper (whereas without preflashing they would only serve to sensitize the paper below the toe portion of the curve and thus produce no visible tone). It thereby appears to accomodate a larger density range negative.
Hope this helps. DJ
-- N Dhananjay (firstname.lastname@example.org), October 22, 1999.
I think you will get surer results using unsharp masking using black and white film to make contrast reducing masks. A reference on dye transfer color printing will have a section on how and why, as well as what films to use and how to expose them.
-- Tony Brent (email@example.com), October 23, 1999.
And you have to be very careful about n+ and n- because of color shifting problems. Masking would be a very viable solution. Just make sure to expose the film properly to give it enough density to begin with. James
-- james (firstname.lastname@example.org), October 23, 1999.
While film and paper emulsions are similar in principle, they differ considerably in practice. A print (or transparency) is viewed directly; its maximum density must produce an acceptable black. To accomplish this, B&W papers are typically developed to completion -- all the silver halide in the latent image is reduced to metallic silver. Further development merely fogs the highlights, while shortened development gives weak shadows.
A negative is not viewed directly; its maximum density need not appear black, and therefore complete development is not necessary. We typically stop its development before the latent image has been completely reduced. By allowing the reaction to proceed more or less (by manipulating time, temperature, and/or agitation), we can increase or decrease contrast and speed.
-- Sean Donnelly (email@example.com), October 25, 1999.
Therefore it is generally feasible to expand or contract a negative, but not a print. As a result, we primarily control print contrast by changing grades (or filtration, in the case of variable-contrast B&W papers). However, some adjustment of B&W paper contrast can be acheived by changing developers.
As pointed out above, contrast manipulation of color materials is even more difficult than B&W, because the three emulsions respond differently, resulting in color shifts and crossover. For this reason, the development processes are more standardized and more closely controlled than for B&W, and expansion and contraction are less feasible. Color printers are therefore forced to resort to techniques such as making a corrected internegative or unsharp masking to manipulate contrast.
-- Sean Donnelly (firstname.lastname@example.org), October 25, 1999.