One of the most important tasks in creating a rich print is controlling the highlight and shadow detail. In my film days, I worried about Zone II and Zone VIII. When working with digital imagery we set white and black points with a similar goal. In the process I’m going to describe, I actually set two different points: one for a dark gray above black, and another for a light gray below white (yes, Zone II and Zone VIII again).
The process starts with printing an assessment target to determine the RGB values that produce these highlight and shadow values using your paper/printer combination. Figure 3 shows my current assessment target. It has boxes of RGB tonal values ranging from 0, 0, 0 to 34, 34, 34 for the shadows, and high- lights ranging from 255, 255, 255 to 221, 221, 221. Because I use a printer that can handle it, I created my test tar- get in 16-bit format.
Once you have created your test chart, bring it up in Photoshop. Select your paper for printing and input all of the characteristics and profile exactly for printing. In my case, I used the Canon imagePROGRAF Export plug- in for Photoshop because I use the iPF 6100 that allows me to import 16-bit files to the printer. This test is only accurate if you exactly duplicate the printing characteristics and input data you’ll use in your final print.
Make your print and allow it to dry for at least 15 minutes. Carefully assess a decent dark gray separation from black (equivalent to Zone II) and a light gray separation from white (equivalent to Zone VIII). For my Canon printer, using Canon’s Polished Rag paper, the dark gray was the 15, 15, 15 value and the light gray 250, 250, 250. Note that these numbers, unlike the absolute black and white points sometimes used, are your first noticeable tone points above and below the extremes. You are now ready to open the RGB image you want to correct, improve, and ultimately print on the paper you just tested.
As an example, in the image I shot of rushing water, I wanted to darken the lower left, lighten the top right, and add some lightness to the water flow. I created a new blank layer and set the Blend mode to Soft Light. Using a Wacom pressure-sensitive pen and a black foreground color, I painted over the lower- left corner of the print until it was sufficiently burned in.
Switching to white as my foreground color, I painted on the rock in the upper right until the shadows were sufficiently opened. With white still my active color, I lightly brushed on the highlight areas of the rushing water to create greater separation in the flow.
Satisfied with my dodging and burning, I created a new Curves adjustment layer. The following steps replicate what I did next. (Note: This description is specific to Curves in CS3 where Levels and Curves adjustments can be done together; those with earlier versions of Photoshop can modify these steps accordingly.)
You now need to pre-visualize a dark tone above black and a light tone below white from the image on your monitor using your previous test assessment. Open Photoshop’s Display Options and select Light. Under Show, select all four of the options. Since the image is in RGB, check Clipping.
Next comes a subjective analysis, similar to how we pre-visualized tones in conventional photography—only now with a visual aid. Look at the image and note two areas of the image where you want the two tones (Zones II and VIII equivalents) to fall. Move the black triangle on the bottom of the Curves preview toward the right until you start to see black (Figure 4). The first black is your pure black. Keep moving until you see your dark tone area also turn black.
Double-click on the black Eyedropper tool. Set the RGB numbers to match the dark gray square from your tonal test chart (in my case, 15, 15, 15). Click OK. Now click carefully on that section of the black area. Be certain that you don’t hit just any black, since both absolute black and your dark tone are presented as black. Be certain to click an area of the image you want to set as the dark gray above black. Note that most of the black areas of your clipping will be removed.
Now move the right white triangle to the left until white reaches the first pure white, plus the white where you want highlight tone. Double-click the white Eyedropper tool and set the RGB numbers to the toned highlight reading from your test chart (in my case 250, 250, 250). Click OK. Now carefully click on the area of the image where you want that light gray to be printed. Again, be careful not to select a pure white area. Most of the clipping indications will be removed.
Deselect Show Clipping. At this point, you should see the curve lines for the RGB number separate and cover the histogram area of your image (Figure 5). You can still work with the neutral line to shape your curves to adjust for lower, middle, and upper tone separation (Figure 6).
When you click OK, Photoshop asks if you want to save your RBG settings as a default. Keep in mind, these settings are only for the paper you selected. Other papers will give you other results. Matte papers, for instance, yield assessment tones much closer together than the two in my example. These two tones, while identified as matching RGB numbers, can also have a color tint when used on a color print.