Your third example, Comparing Statistical Normal Conditions with Film Processing Adjustment Example, looks like a very clear illustration of what N-2 and N would be. (Plus you've adjusted for flare which I like because it looks like a real world example.).
It's more of a guide for comparison. Yes it would be near impossible to match the values, and you wouldn't want to even if you could. I'll do a post on that later. Maybe in a new thread.
Originally Posted by Bill Burk
The curve in the normal 4 quadrant is what you want. Lighter than the original scene with a mid-tone gradient slightly higher than the original.
I have been interested recently in the fourth quadrant curve of the "preferred" curve - that the 45-degree angle perfect curve is actually not attractive and there is a curve that is psychologically preferred. You may have shown that in recent posts? As I recall it is up and to the right of the 45-degree line but similar to your "normal" curve here. Is that right?
Last edited by Stephen Benskin; 02-24-2012 at 10:09 PM. Click to view previous post history.
Last edited by Stephen Benskin; 02-24-2012 at 10:31 PM. Click to view previous post history.
This is kind of interesting. In normal and nine stop comparison example, I aligned the curves at the highlight. Here is how they look without the adjustment.
Sorry, the example below has the same alignment as the first example of the normal to 9 stop comparison, but instead of readjusting the tone reproduction curves to align them with the highlight, I've adjusted the placement of the 9 stop luminance range so that both examples have the highlight to equal 100%. This way the metered exposure guide (dark dotted line) aligns correctly.
Last edited by Stephen Benskin; 02-24-2012 at 11:55 PM. Click to view previous post history.
Of all the potential factors that have an influence on the photographic process, the elimination of one would greatly simplify the process and make it fairly straight forward. All you would have to do is match up the negative density range to the paper log exposure range and the final print will match the original scene’s luminance range. That factor is us. How our eye and brain works adds an additional set of rules, variables, and exceptions on top of the simple curves we attempt to interpret. This area of study is subjective tone reproduction. I’ve included an excerpt from The Theory of the Photographic Process.
“The theory of subjective tone reproduction is concerned with the problem of reproducing the brightnesses of the original scene. [Brightness, in the terminology proposed by the Optical Society of America and adopted in this book, is the magnitude of the subjective sensation produced by light and luminance is the magnitude of the stimulus (light)] If the brightness of each point in the illuminated photograph is equal to the brightness of the corresponding point in the original scene, the photograph and its associated illuminance and surround are considered to be a combination that provides exact, subjective tone reproduction.
The achievement of exact reproduction of the scene luminances in an illuminated photograph does not necessarily mean that exact reproduction of the scene brightnesses will be obtained. If the angle subtended by the photograph is the same as that of the scene, and if the field of view surrounding such a photograph contains luminances that place the eye in the same state of adaptation and inhibition that it was in when the original scene was viewed, both exact luminance reproduction and exact brightness reproduction will be realized simultaneously. But the surround luminances that exist in viewing a photograph (as, for example, in viewing a slide transparency projected in a darkened room) are frequently very different than those that existed in viewing the original scene and, hence, the eye is seldom in the same state in the two situations. Very often, therefore, exact luminance reproduction would not produce exact brightness reproduction.
The illuminance on the photograph generally must be greater than that on the original scene if exact luminance reproduction is to be obtained. The reason for this requirement is that the semispecular reflections from shiny objects in the scene, such as hair, eyes, certain areas of the skin, jewelry, certain types of cloth, glassware, ceramics, fur, shiny leaves, rippling water, and many metallic objects, usually have a luminance greater than that of a diffuse white object in the scene. If the diffuse white object were to be recorded at the maximum reflectance of the photographic paper (approximately 90%), the shiny areas of the scene could not be reproduced at the required higher luminances. For true reproduction, therefore, the diffuse white objects in the scene must be recorded at a reflectance less than 90% so that the shiny areas in other objects can be recorded at 90% and thus have a luminance higher than that of the photographic record of the diffuse white objects. If, for example, the diffuse white objects in a living-room scene lighted with 100 foot-candles are reproduced so that they will have a reflectance of 45% in a photographic print and the brighter, semispecular objects are reproduced at a reflectance of 90%, the illuminance on the photograph must be 200, rather than 100, foot-candles. Similarly, the illuminance on a photograph of a sunlit scene must be considerably more than 10,000 foot-candles if exact luminance reproduction is to be achieved.
One of the important problems in photographic tone reproduction is that of reproducing the appearance of average outdoor scenes lighted with sunlight plus skylight. The illuminance on these scenes usually lies between 5000 and 10,000 foot-candles, depending on the angle between the sun and the principal plane of the main subjects in the scene. The photographs of these scenes, however, are usually viewed in homes, offices, classrooms, or art galleries where the illuminance is usually in the neighborhood of 50-100 foot-candles or less. The luminance of a white area in the photograph is then roughly one-hundredth the luminance of the corresponding white area in the sunlit scene; it is, in fact, roughly equal to the luminance of a nearly black object in the scene and yet it appears to be a satisfactory reproduction of a white object! It is only because of the remarkable ability of the eye to compensate for the low level of lighting, by increasing its sensitivity, that photographs can be viewed satisfactorily at the levels of illuminance commonly used in buildings. Exact luminance reproduction of sunlit scenes is not ordinarily attained in viewing photographs and, because of the properties of the eye, it is seldom required for satisfactory subjective tone reproduction.”
“The gradient in the middle tone region was always greater than 1.00 (usually 1.10 – 1.20) for the preferred point of all the scenes studied. Whenever the middle tone gradient was less than 1.10, the prints were unanimously rejected as being “too flat.” Whenever the density level of the prints was great enough so that the curves closely approached the 45-degree reference line, the prints were unanimously rejected because they appeared too dark.”
Last edited by Stephen Benskin; 02-25-2012 at 09:06 PM. Click to view previous post history.
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This should be relatively easy to represent in the fourth quadrant graph... And it would be interesting to see the film and paper curves that contribute to the preferred result.
Originally Posted by Stephen Benskin
Last edited by Stephen Benskin; 02-26-2012 at 10:42 AM. Click to view previous post history.
Where a curve is measured can result in different gradient values. Gradient is a function of the degree processing has on the densities of the film. The problem is where to measure the curve to determine the gradient value. The most obvious answer would be the area of usage, but even that can have it’s difficulties when considering factoring in flare or not. Another is to use the average exposure range and assume the curve is relatively consistent enough to apply to other exposure ranges. This can work well for short toed curves with their long linear curves, but not so with long toed curves, where the point of measurement can be more critical.
At this point I don’t want to make any judgments as to the best gradient method. I just wish to illustrate how the value is effected by the type of curve and where it is measured.
The first example has three curves. Using the Contrast Index method, Curves A and C are the same contrast. Curve B is slightly higher. Depending on where the curve is measured, A can have a higher gradient than B.
The following examples come from a graph uploaded by Chuck. I’m using it only because it is an excellent example of a short toed curve and a long toed curve that come together at one of the points measured. At the Zone VIII log-H indication (2.10 log-H range), they both have a density of 1.30 (1.20 density range over 0.10 Fb+f). If measured from this point, the two curves will have the same gradient. But what about other points.
The first example shows Alan Ross’ Zone IX method (2.4 log-H range), Ilford’s Average Gradient Method (1.50 log-H range), and a check at a range of 1.80 log-H.
The next two use the Contrast Index template. The template is moved back and forth along the curve until the gradient in the small arc matches the gradient in the larger arc.
The last two examples comes from the template in Beyond the Zone System. This template has a series of tiered arcs to accommodate longer scene luminance ranges. Instead of a smaller arc in the toe, it uses a fixed density point of 0.17 over Fb+f.
Last edited by Stephen Benskin; 02-26-2012 at 11:34 PM. Click to view previous post history.
Thanks for the illustrations with the different indices points' we've been talking about shown in overlays on the graphs! Thanks Chuck for providing the excellent example.
If you illustrated this with just a D-76 graph, the wrong conclusion might be reached. With only D-76 you would think there is no difference which method you use. But HC-110 shows clearly that when the curve is not a straight line, you can get different results almost 0.10 different.
Now I have no illusions about my own process. I have 0.10 variation in my process when I am "out of control" but even in that situation my negatives are "fine".
I think they illustrate why people can have difficulty exchanging processing values.
Last edited by Stephen Benskin; 02-26-2012 at 10:27 PM. Click to view previous post history.