In practice, the 256 level scale is geared to accurately placing images on a printing press. In reality, each level occupies less than one percentage of dot on press. Presses have ink limits that do not exceed 100% for any of it's colors, which translates to 100 possible tonal differences. The most fabulous press in the world would be challenged to print 70 visually discernable tones, and I'd guess an average sheet fed press might print 50-60 discernable tones. Why should I be concerned with less than one-half dot% accuracy when I cannot have 2% dot accuracy on press? Even the most accurate output device in the printing industry, the imagesetter, is callibrated to a 1% error value. There is no ability to specify and receive any specific gray level on press; in fact there is no way to even measure gray levels on press.

In normal practice, the digital capture is made and the endpoints are adjusted (using software, or lighting, or both). The density range (the number of tones between highlight and shadow) is fine tuned with a Levels command and the transition of tone is re-mapped with a Curves function, usually applied in Photoshop. For most digital captures the proper exposure and transition of tone are implemented with a target made by Kodak called the Q-14. This target has 20 different shades of gray on it starting at white and incrementally gaining in density with the lowest reflectance becoming black. The lowest reflectance reads 19 which indicates a density range of 1.9D. Each reflectance is numbered and indicates the density range between it and the brightest patch on the gray scale. Usually aimpoints are indicated to the photographer; he must make sure that specific reflectances read nominal values specified by the separator or printing press. The photographer must then adjust a characteristic curve in a software program to make the reflectances read the specified value. Choosing the the appropriate density and transition of tone from within the Curves dialog box traditionally relies on the monitor representation as a guarantor of predicting the outcome of the adjustment. Photoshop's (and many other image editing packages) Show Info dialog box reports a "before" and "after" of any sampled point in the image. Most usual is the display of RGB (0-256), or CMYK; whose subtractive color space and gray component make difficult the understanding of what density the sampled reflectance really is. If this described picture making process does not remind you of photography, we're in agreement. In actuality, this procedure is the application of a scanner interface and I think it has very limited relation to traditional photographic proceedure.

As photographers, we know that making changes to the number of tones (and their transitions) after the capture has some drawbacks. Graded papers are largely misused (they're often used for density range correction rather than the gamma correction they're really designed for), flashing prints often veils highlights, and over-extended developments commonly result in fogging the opposite end of the scale. How we might wish for the negative that makes the "straight print"! Digital is no different, but how do we know when we've done it right? We know we cannot trust the monitor, so we use the info report. The traditional 256 level information report makes our task all the more difficult because it's not an intuititive progression.

I spent 9 months with MegaVison teaching digital photography in 256-0 and 0-100 scales before it dawned on me that I could use the T2's 0-100 Show Info report scale to infer Zone System values of 0-10; a one's place is the difference between the two number progressions. MegaVision has since added to their software, a 0-10 Show Info that reads direct zone values. This has greatly improved my ability to communicate photographic concepts to new users. Although most shooters haven't thought about the Zone System since their photo school days, they find the approach vastly superior to the 256 scale.

One inherent advantange the Zone System has when considering the evaluation of reflectances, is relative placement on multiple targets. Consider that zone II is the same distance from maximum black and minimum white on all targets, regardless of media or density range (neg, chrome, color, b&w, inkjet, dye sub, monitor, or printing press). The other Zone System values are no different, they have the same relationship to absolute black and absolute white on all targets. It's traditional to use terminology relating to the target when discussing value. Printers use ink densities, scanners use gray levels, photographers use f-stops or zones. The zone system allows the use of a terminology photographers can use for all of these targets because zones relate easily to other targets, unlike ink densities on monitors or gray levels on press.