Let’s look at how this works in practice. The image in Figure 3 needs serious help (this is what happens when undeveloped film winds up going through x-ray machines about twenty times because the airline lost your luggage).
Figure 3: This image needs serious help!.
If we simply accept the default settings, we get a very high contrast and rather cold rendering, even if it’s a great improvement over the raw image. Highlights such as the tops of the buses are blown out to solid RGB 255 white, and the shadows are very murky, as shown in Figure 4.
Figure 4: We need to repair the blown-out highlights and murky shadows.
We can improve matters greatly by adjusting the clipping percentages. The image updates as you change the settings, and the info palette provides before-and-after values, so the whole process is quite interactive. When you’re starting out, and just getting a feel for the way the controls work, I suggest setting the shadow and highlight clipping percentages to 0 (no clipping) as a starting point, and increasing them gradually from there until you get the result you want. The change from 0 to 0.01% is bigger than you might expect.
An easy way to see what’s happening as you adjust the clipping percentages is to use the arrow keys instead of typing numbers into the fields. Highlight the field whose value you want to edit, then press the up or down arrows to increase or decrease the percentage in 0.01% increments: Add the Shift key to go in 0.1% increments instead. That way, you can place the cursor on a highlight or shadow in the image and watch what happens to the values in the info palette as you adjust the clipping percentages. Using this technique, it takes me about three seconds to decide that the shadow clipping percentage should be 0%, and the highlight clipping percentage should be 0.02%, producing the result shown in Figure 5.
Figure 5: Adjusting the clipping percentages to 0% for shadows and 0.02% for highlights gives much better results.
The aforementioned edits produce a decent dynamic range — the shadows are pleasantly open, and the hottest spots in the highlights are all still below level 250 — but the color balance is still rather cold. Adjusting the midtone target color lets you fix the color balance in the same round of edits. Click on the midtone gray swatch in the Auto Color Correction Options dialog box to open the color picker, which in turn lets you change the target color, as shown in Figure 6.
Figure 6: Now change the target color to fix the color balance.
As with the clipping percentages, changes to the target color are immediately reflected in the image, so the process is interactive. You can adjust the target color either by changing the numbers in the numerical fields (the arrow keys work here too — up and down arrows change the value by 1, adding the Shift key changes the values by 10), or by dragging the little circle around in the color swatch, or a combination of the two. (I often find that adjusting the HSB numbers is quicker and easier than adjusting the RGB ones.)
In this case, I obtained the result shown in figure 7 by first raising the Red value and lowering the Blue, then dragging the circle in the color swatch until I obtained the visual result I wanted.
Figure 7: Changing target color is interactive so I raised the red value and lowered the blue until I got the result I wanted.
This article was last modified on January 3, 2023
This article was first published on July 23, 2002
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