Digital BW, The Print

In the long running ,and often dense, discussion of which media has more tones, silver or inkjet (which lead to the dynamic range thread), I have done a lot of thinking and have a hypothesis for the difference people see.

This is prompted by the fact that on a couple of occasions silver printers have claimed that they got better tonal renditions by printing on matte silver paper than smooth silver paper. At the time I was more than skeptical, but I think that after having heard similar statements about inkjet quad prints, which also happen to be on matte paper, I may have come up with an explanation.

Just to keep things clear, my goal in printing is to achieve a silver or inkjet print that appears to be a continuous tone image without steps. Especially in natural gradients such as skies. What the images may actual do at a microscopic or theoretical level is not of interest to me at the moment.

When I expose a negative using the zone system, I am deciding what shadow and highlight areas of the scene need to hold detail to achieve my artistic vision. I measure each and choose an exposure/development combination that (hopefully) will put the shadow details on Zone III and the highlight details on Zone VII. (Adams went wider but I like to play it safe.)

Once I have the negative in the enlarger or in the scanner/computer system, I will try to place the Zone III value at some gray that is just enough lighter than the maximum black (maximum print density) of the paper medium and Zone VII at some light gray that is just enough darker than the brightest white (minimum print density which is the white of the paper base) so that detail can be seen in both these areas.

Now if I am printing on smooth silver paper the Zone III value will be a little lighter than the darkest black of the silver paper, which has a density of 2.2, and the Zone VII value will be a little darker than the white of the paper base, a density of about 0.06. So my Zone III to VII range is spread close to the limits of a density range of 2.2 minus 0.06 or 2.14. This would be a reflectance range of 90.6 percentage points.

If I am making an inkjet print I do the same thing. The only difference is that my Zone III value will be just lighter than a density of 1.7 and my Zone VII value will be just darker than a density of 0.04. So here my Zone III to Zone VII range is spread over a density range of 1.66. This would be a reflectance range of 85.1 percentage points.

Now if we have done a good job of printing and our materials are good, both images will appear to our eye to have continuous tones without any visible breaks or sudden steps in smooth gradients and certainly no posterization. Both prints will have mapped the tones in the scene we photographed to the print with a degree of accuracy to convince our eyes that nothing has been lost.

So why do some people say there are more tones in the inkjet print? I think that this is an issue of the function of the human eye.

As you know the human eye can see detail across a range shadow and bright light that far exceeds what we can capture on film. When we go outside we can see detail in deep shadows and details in bright areas that are difficult to impossible to get onto one negative at the same time. This seems to me to be largely due to the fact that the iris of our eye continually gets larger or smaller as we scan across the scene like a very sophisticated auto-exposure mechanism to allow us to see over a huge range of brightness levels. In addition to the iris of our eye, the sensitivity of the retina also adjusts to light levels but much more slowly.

Now when we view a photograph I assume that at a normal viewing distance the print fills a significant portion of the center of our field of view, the light source is constant and that our retinas have stabilized at a level appropriate to the lighting. Under these static conditions I believe that the size of our iris is steady along with our retinal sensitivity. Under these conditions I believe that we can only perceive a limited range of light to dark or that our ability to discern tones declines as the tones reach the end of this range..

My theory is that under these print viewing conditions the range of light to dark our eyes can perceive is more closely matched to the reflectance range of the inkjet or silver matte print than to the air dried or glossy silver print. I further theorize that this is more evident in the dark tones than in the light. I think we may clearly perceive the lightest tones of both prints but that in the shadow areas we cannot see the detail in the shadow area of the silver print unless we do something to cause the iris of our eye to expand or the retinas to become more sensitivity. This can be done by getting closer to the darker areas of the print or by placing them more directly in the center of our field of view.

I demonstrated this to some degree with my own eyes by placing an inkjet and an air dried silver print side by side under the same light. I then varied the viewing distance and compared my ability to see detail in the deep shadow portions of the prints. My rough approximation is that I could see all of the shadow detail in the inkjet print at about double the distance at which I could see all the shadow detail in the silver print.

Both prints appear to my eye to contain the same amount of shadow detail but it is easier to see in the inkjet print since the shadow detail is within the static range of brightness that eyes can encompass at a normal viewing distance.

I hope that all of that makes some sense and it would be great if there was an ophthalmologist in the audience to comment on the behavior of the eye and the perhaps the eye/brain interface which also may play a part.

Thanks,
Martin Wesley




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