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Virtual gradations

In the analog darkroom, the gamma value and thus the contrast of a black-and-white photograph is ultimately controlled by the choice of paper onto which the negative is printed, namely by the associated choice of gradation.

In ColorPerfect, unlike in our old plug-ins and the analog darkroom, the Gamma image adjustment can also be used artistically for color images without any degradation of color reproduction.

Only for black and white negatives and not for color films, the mechanisms of film gamma or paper gamma can be used equivalently for artistic purposes, which makes it possible to offer you a set of film characterizations for ColorNeg mode as a reference for working with your black and white negatives.

In this context, we speak of Virtual Gradations. This work aid is available here and again at the very bottom of this page as a *.negpos file for download.

Relation to actual paper gradations in the analog darkroom

Our Virtual Gradations for the ColorNeg mode in ColorPerfect are modeled after actual paper gradations of fixed graded RC papers. They behave similarly to paper gradations in the darkroom, but not exactly the same. One aspect of this is that there is no black point in the analog world, since too much light emitted on photographic material cannot simply be retracted.

It is also less urgently needed there, since there are no additional hidden signal components from the electronics in addition to light in the darkroom. Nevertheless, the characteristic of the photo paper's light sensitivity takes over part of its function there.

Influence of gradations on the image

When working with differently graded paper, choosing too low a gradation will result in a flat print. This means that, depending on the exposure, such a print will contain either no pure white or no pure black, and so will not be ideally graded even in the midtones.

ColorNeg always fixes the former of these two aspects for reasonably well exposed negatives. Regardless of the Virtual Gradation being worked with, it is possible for the photographer to utilize the full tonal range from black to white. This is related to the implications of the digital black point discussed earlier.

An image adjustment equivalent to it, however, can also be modeled with the adjustments of "Black" and "White" that underlie our system of complete color integrity, which can also be described as brightness and haze.

The initial situation in the digital image therefore appears no less natural or familiar than its analog counterpart.

Gamma and/or Virtual Gradations affect contrast without affecting the extremes of black and white in the image.

Excursus on "Black" and "White" in ColorPerfect - Word origin and slider direction

The terms "Black" and "White" used above for image content are two words that can lead to extensive misunderstandings in relation to ColorPerfect. Indeed, there are image adjustments of the same name in the plug-in, but they do not work in the way the uninitiated user might expect. So a little digression can't hurt.

"Black" and "White" in ColorPerfect work, in one sense, as if an equal amount of black and white paint, respectively, were added to each color in the image on a painter's palette. In the other direction of adjustment, the magic of digital comes into play, because here black or white paint can also be removed from such a mixture.

This may sound unnatural at first. On closer inspection, however, far less so. Our imaginary painter would certainly have saved the main part of his color supply and mixed black and/or white only into a small part of a color on the palette at all. Thus he could still subsequently produce any shades between the full color and the tinted color. So much for the naming.

Now painting is not every photographer's cup of tea, so the metaphor may not seem catchy to everyone. So, if necessary, remember that "Black" in ColorPerfect means brightness in the sense of darkening, and "White" in ColorPerfect means the removal or, more rarely, the addition of haze or fog, which brings us right back to the world of natural scenes and light.

The slider direction is more in line with the second metaphor anyway, that of light. It is possible to lighten the image in each case in the same scroll direction (up), although this requires removing black on one side and adding white on the other.

The fact that fog and haze accumulate in the spatial depth of the image, so that different parts of the image may well need different adjustments by means of selections for a natural image result, is mentioned here only in passing.

Excursus on "Black" and "White" - Influence on highlights and depths

To get back to the extremes of black and white in the black and white image, we'll briefly go over what image adjustments are used to influence them in ColorPerfect.

The brightest tonal values in the image result from the prevailing image brightness, which is primarily influenced by the "Black" image adjustment and can be fine-tuned by compressing the highlights.

The darkest tonal values in the image result, on the one hand, from the predominant setting for "B Point", the black point or "BP Tails", which in turn controls the black point. On the other hand, they result from the settings for the "White" image adjustment.

After we have already spoken of the compression of the highlights, it is probably worth mentioning that the area of influence of the "White" image adjustment alone is covered by the compression of the depths, that is, by that for the tonal values of the shadow regions.

What is once without brightness by "BP Tails",the black point adjustment, should and must remain so as long as this very setting does not change.


Influence of gradation or film and paper gamma on tone reproduction

After describing what affects the extreme tonal ranges, we return to why this concerns us here: Our virtual gradations do not cause areas of the black and white photo to fade to pure black or burn out but control the contrast of the intermediate tones.

Generalizing, in the following we use the term positive gamma as a generic term for the paper gamma and its digital equivalent.

To obtain the most natural reproduction of the tonal values of a grayscale image, the condition film gamma * positive gamma = 1 must be met. This has nothing to do with the gamma encoding used in the digital world, but refers solely to the characteristics of the film.

Emanuel Goldberg described this fact in his 1922 book "Der Aufbau des photographischen Bildes" (The Structure of the Photographic Image), so the above condition is also known as the Goldberg condition or Goldberg rule. Neither of these terms is in common use today, but we will still use them in the following to give the circumstance a simple name.

Thus, the virtual gradation at which the most lifelike grayscale reproduction is achieved depends on adherence to the Goldberg rule.

As in the darkroom, the other gradations can be used freely according to artistic criteria. A total of 13 Virtual Gradations between 00 and 5 are available in half gradation steps. Compare the effect of each Virtual Gradation using the versions shown of the same normally exposed and developed negative: Virtual Gradation 00, 00½, 0, , 1, , 2, , 3, , 4, , 5.

For the example, the most natural grayscale rendering is achieved by using Virtual Gradation 2. It represents the point at which the Goldberg rule applies to normally developed negatives. Since the ideal positive gamma depends directly on the gamma value of the negative, different Virtual Gradations achieve the most natural rendering for differently developed negatives according to the following list:

Virtual Gradation 2 for normally processed negatives (Gamma 0.62)

Virtual Gradation 1 for Push 1 processed negatives (Gamma 0.70)

Virtual Gradation 0 for Push 2 processed negatives (Gamma 0.85)

Virtual Gradation 00½ for Push 3 processed negatives (Gamma 1.00)

Virtual Gradation for Hold 1 processed negatives (Gamma 0.55)

Virtual Gradation for Hold 2 processed negatives (Gamma 0.45)

Because all Virtual Gradations are derived from actual photo paper gradations, the gradations listed do not correspond to the exact point at which the Goldberg rule applies to the gammas listed, but rather values in close proximity to the points you would determine by calculating the corresponding inverse gamma values. In practice, you will also not exactly adhere to the listed gamma values during development.

Why a gamma value of 1 does not lead to the best grayscale image

Some users asked if it would not be best to always use a gamma value of 1 in ColorNeg for converting black and white negatives. This setting corresponds to the "B&W Start" value hard-coded into the user-specific film menu, with the second part of the name indicating that this is only intended as a starting point.

The assumption that this results in an unchanged grayscale image is incorrect in that film does not operate linearly but usually has a film gamma significantly less than 1.

Under artistic criteria, there is nothing to be said against using the Gamma 1 scrollbar setting in conjunction with "B&W Start" in ColorNeg mode, provided this produces the desired results. We merely point out that such a gamma value corresponds to the setting that leads to the most natural tonal gradation for Push 3 developed negatives. This is roughly equivalent to the result that would be obtained by using Virtual Gradation 00½.

If you apply this Virtual Gradation to the above example for testing, it becomes clear that this is not the optimal value for converting normally developed and exposed negatives.

New image adjustments in ColorPerfect to complement our Virtual Gradations

The concept of Virtual Gradations was conceived over 10 years ago, when we had just completed our first software for PCs and Macs that was accessible to a wider audience: our original ColorNeg plug-in.

Virtual gradations have enjoyed some popularity with black-and-white photographers ever since, but the original article on them was difficult to read in the context of ColorPerfect, so it has been revised to reflect the new plug-in.

ColorPerfect brought other new features that you should definitely try in conjunction with the virtual gradations.

For one, as the most flexible tool, the image adjustments under "Zones", whose help texts in the plug-in are worth reading, but whose detailed description on this subpage is beyond the scope.

On the other hand, as one of our favorite tools, the "Graded White" function. In fact, there is hardly a color or black-and-white image anymore in which we would not apply "Graded White" to a small or large extent in the direction of removing white.

This image adjustment is somewhat hidden. The name of the "White" function is a button that changes to "Graded White". "Graded White" behaves like combining a luminance mask with the "White" function. That is, the brighter an image part is the higher the degree of white removed from its color or added in the opposite direction of use (the rarer case).

In conjunction with Virtual Gradations, it is a good idea to use a slightly lower gradation, so that by removing "Graded White" the contrast can be fine-tuned.

It should be noted that the function makes the numerical output of pixels becoming zero in the area of compression of the shadow portions of the image less meaningful. Namely, it also counts those pixels whose graded part becomes zero by removing white, even if it is the much smaller part, so that this does not apply to the whole pixel.

With moderate reduction of "Graded White", compression of shadow regions can often be omitted. However, if it calms you down you can use a value of, say, 4 there to eliminate the numerical effect. You will certainly find your preferred way of working.

Anyway, we invite you to explore these innovations and to ask us about them.

Loading and saving characterization files with ColorPerfect 2.15 and higher

With ColorPerfect 2.15 and later, characterization files can be stored in any location as plain text files with a freely selectable (short) file name. The only requirement is that you use the specific file extensions instead of *.txt.

Use the file extension .negpos for ColorNeg mode, .colorint for ColorPos mode, and .pfraw for PerfectRAW. After you have selected the entry "User" from the manufacturer menu instead of e.g. Kodak, you can comfortably work with the files by means of file open or save dialogs.

You can download the Virtual Gradations here as a *.negpos file.