Another common way to use Levels for managing contrast is through the use of the Eyedroppers. The Eyedroppers are in the lower right hand corner of the Levels dialog box (see Figure 1). The left Eyedropper is the Black Eyedropper and is used to set the black point or shadow values. The right Eyedropper is the White Eyedropper and is used to set the white point or highlight values. The middle Eyedropper is the Gray Eyedropper and is used to set neutral gray in the image. In the Eyedropper approach, the Black and White Eyedroppers will be used to set the shadow and highlight values respectively.
Figure 12 shows the Levels dialog box after the highlight values have been set. Comparing this dialog box to the one in Figure 1, it can be seen that the right side of the histogram has moved closer to the right side of the chart. More of the empty tonal values have been eliminated.
Some might question why we don't move the right side of the histogram even closer to the side of the chart. The answer lies in color sampler #2, as shown in the Info palette (see Figure 13). The Info palette shows that the highlight at color sampler #2 has values of 252, 252, 251. When color sampler #2 was placed, it was determined that this point should have the lightest tone that still has detail. These three color values are already very close to 255. If the histogram was moved any closer to the right side of the chart, these values would go to 255. This would result in this point going to pure white (i.e., there would no longer be any detail). Additionally, it would result in clipping of some of the highlights.
This point illustrates the importance of using color samplers. By just looking at the histogram, the tendency would be to try to click the White Eyedropper somewhere else that would bring the right side of the histogram closer to the edge of the chart and get rid of some more of the empty tones. The problem is that those tones are not really empty. However, that becomes obvious only when the Info palette is studied. Using the Info palette and the color samplers prevented clipping of the highlights in this image.
While the image definitely looks better, a little extra contrast wouldn't hurt. Thus, the last step is to use Levels to adjust the midtone contrast by using the Gamma Input Slider. As before, moving the Gamma Input Slider to the right increases contrast. Moving the Gamma Input Slider to the left decreases contrast.
A Gamma Input Slider setting of 0.88 creates the desired contrast. Figure 16 shows Levels with the final set of shadow, highlight, and Gamma Input Slider settings.
Figure 17 shows the Info palette after all of the adjustments have been made. It can be seen that the Gamma Input Slider adjustment slightly changed the values for the shadow values. This could be adjusted with the appropriate slider. However, for this image, the changes are slight, so no further adjustments will be made. Clicking the OK button closes Levels.
Figures 18 and 19 show the original image and the image after all the adjustments were finalized.
The previous techniques all used the RGB channel. Thus, all three colors were adjusted at the same time. This works well for most images. However, sometimes it is desirable to adjust each color channel separately. This is most often the case when the color histograms have significantly different shapes. In this situation, the individual color channel technique is an option. Figure 23 shows an unedited image that falls into this category. Figure 24 shows a histogram of this image. It can clearly be seen that the color channels have different shaped histograms that start and stop at different points.
To start the editing, Levels is launched.
Next, the Channel pop-up is accessed (see Figure 27), which reveals the three color channels. For this example, the red channel is selected. The red channel is now displayed (see Figure 28). All edits performed will affect only the red channel.
The last step is to set the midtone contrast. This is done by adjusting the Gamma Input Slider in the RGB channel as shown in Figure 42. It is important that this is done in the RGB channel. Making changes to the Gamma Input Sliders in the individual color channels will cause color shifts in the image. This particular image does not require any contrast adjustments, so the Gamma Input Slider is not adjusted. Clicking the OK button closes Levels.