Levels -- Part II

Article and Photography by Ron Bigelow

www.ronbigelow.com

Photoshop CS or Photoshop CS2 Used in this Tutorial

Shadow Values, Highlight Values, and Midtone Contrast: Eyedroppers

Figure 1: Eyedroppers on Levels Dialog Box

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 2: Image with Three Color Samplers

One of the advantages of the Eyedropper approach is that the shadow and highlight values can be made neutral. The drawback is that forcing these values to be neutral can sometimes cause color shifts in the rest of the image. It is therefore necessary to track the color values at three tonal locations: the shadows, the highlights, and the midtones. This is easily done with the Color Sampler and the Info palette. Once Levels is opened, the three color samplers are put in place. The first two color samplers are set down in the shadows and highlights as was done in the Info Palette Approach. The third color sampler is set down in an area of midtones. This area should be as neutral as possible. Figure 2 shows the image with the three color samplers. Figure 3 shows the info palette with the color values of the three color samplers.

Figure 3: Info Palette with Color Values at the Three Color Samplers

Figure 4: Black Eyedropper on Levels Dialog Box

To set the shadow values, the Black Eyedropper is double clicked (see Figure 4).

Figure 5: Color Picker Dialog Box for Selecting Target Shadow Color

The Color Picker dialog box appears as shown in Figure 5. This Color Picker is used to set the shadow values. These values will then be assigned to whatever point is clicked with the Black Eyedropper. The values are set by entering the values directly into the R, G, and B boxes. The values should be set between about 2 and 8. The lower the value, the darker the shadows will be. As long as the same value is entered into each of the three boxes (e.g., 5 in this case), the shadow values will be neutral. Clicking OK closes the Color Picker.

Figure 6: Black Eyedropper Clicked at Sampler #1

To set the shadow values, the Black Eyedropper is simply moved around the dark areas of the image (the curser turns into the Black Eyedropper as it is moved over the image). As the Black Eyedropper is moved around, the Info palette indicates the tonal values (for the three color channels) of the location directly below the Black Eyedropper. For the setting of the shadow values, it is desired to find a position that has very low tonal values but still holds detail. It is also a good idea for the position to be fairly neutral (i.e., the three tonal values are approximately equal). However, such a point was already located and identified with color sampler #1. Therefore, the Black Eyedropper is simply clicked at the location of color sampler #1 (see Figure 6). This will set the shadow values.

Figure 7: Levels Dialog Box after Shadow Values Were Set

Figure 7 shows the Levels dialog box after the shadow values have been set. Comparing this dialog box to the one in Figure 1, it can be seen that the left side of the histogram is, now, just barely touching the left side of the chart. In other words, we have gotten rid of the "empty" tonal values. Now, the blacks start just at the left edge of the histogram. This has increased the contrast of the image.

Figure 8: Info Palette after Black Eyedropper Clicked at Sampler #1

The Info Palette (see Figure 8) shows the result of this work. Sampler #1 has values of 4, 4, 4 (a nice neutral shadow). One might be tempted to ask why the values are not 5, 5, 5. After all, that is what was set in the Color Picker for the shadow values. The answer resides in the small difference in position between Sampler #1 and where the Black Eyedropper was set. The curser is simply not accurate enough to align them perfectly.

Figure 9: White Eyedropper on Levels Dialog Box

To set the highlight values, the White Eyedropper is double clicked (see Figure 9).

Figure 10: Color Picker Dialog Box for Selecting Target Highlight Color

The Color Picker dialog box appears as shown in Figure 10. This Color Picker is used to set the highlight values. These values will then be assigned to whatever point is clicked with the White Eyedropper. The values are set by entering the values directly into the R, G, and B boxes. The values should be set between about 245 and 254. The higher the value, the lighter the highlights will be. As long as the same value is entered into each of the three boxes (e.g., 250 in this case), the highlight values will be neutral. Clicking OK closes the Color Picker.

Figure 11: White Eyedropper Clicked at Sampler #2

To set the highlight values, the White Eyedropper is simply moved around the light areas of the image (the curser turns into the White Eyedropper as it is moved over the image). As the White Eyedropper is moved around, the Info palette indicates the tonal values of the location directly below the White Eyedropper. For the setting of the highlight values, it is desired to find a position that has very high tonal values but still holds detail. It is also a good idea for the position to be fairly neutral. However, such a point was already located and identified with color sampler #2. Therefore, the White Eyedropper is simply clicked at the location of color sampler #2 (see Figure 11). This will set the highlight values.

Figure 12: Levels Dialog Box after Highlight Values Were Set

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.

Figure 13: Info Palette after White Eyedropper Clicked at Sampler #2

The Info palette also provides anther very important piece of information. Sampler #3 shows what has happened at the midtones. A look back at Figure #3 shows that color sampler #3 had values of 160, 157, 160 before any image editing. While this point is not perfectly neutral, it is pretty close. Figure 13 shows that after editing, color sampler #3 has values of 180, 180, 179. While the values have sifted (as would be expected), they are still pretty close to neutral. This shows that setting the shadow and highlight values with the Eyedroppers did not cause any significant color shifts in this image.

Figures 14 and 15 show the original image and the image after the shadow and highlight values were set.

Figure 14: Original Image

Figure 15: Image after the Shadow and Highlight Values were Set

Figure 16: Levels with the Final Settings

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: Info Palette with the Final 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.

Figure 18: Original Image

Figure 19: Image after all Adjustments were Made

One of the advantages of the Eyedropper approach is that it gives neutral shadows and highlights (if the Color Picker is set up properly). The downside is that forcing the shadows and highlights to be neutral can cause color shifts. Figure 20 and 21 illustrate this problem. Figure 20 shows the image as adjusted above. Figure 21 shows the image with the White Eyedropper clicked in a less carefully selected position. When comparing the two images, it is clear that a color shift has occurred in the second image. This is confirmed by viewing the Info palette in Figure 22. Sampler #3 is no longer neutral as was the case previously.

Figure 20: Image with Final Adjustments as Made Above

Figure 21: Image with Color Shift Due to Poor Use of White Eyedropper

Figure 22: Info Palette with a Color Shift Problem

Shadow Values, Highlight Values, and Midtone Contrast: Individual Color Channels

Figure 23: Image with Different Shaped Color Histograms

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.

Figure 24: Each Color Channel has a Different Shaped Histogram

As with the previous techniques, the first two tasks that need to be performed are to set the shadow values and the highlight values. However, with this technique, we would like to be able to watch what is happening with all three color channels at the same time. Unfortunately, Levels will only allow one histogram to be viewed at a time. This situation can easily be remedied by the use of the histogram tool. Histogram is launched by choosing Window/Histogram. The Histogram palette will look something like the one shown in Figure 25 (the histogram may look slightly different depending on how it is configured). The options for the Histogram are set by clicking on the pop-up in the upper right hand corner of the palette and choosing All Channels View. If the channels are not in color, clicking on the pop-up again and choosing Show Channels in Color will render each histogram in its appropriate color. Figure 26 shows the Histogram with all three color channels.

Figure 25: Histogram

Figure 26: Histogram with Color Channels

To start the editing, Levels is launched.

Figure 27: Levels Channel Pop-Up Accesses Color Channels

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.

Figure 28: Red Channel in Levels

The shadow and highlight values can now be set similarly to the way they were set in the eyeball technique. The only difference is that the edits only affect one color channel at a time. To set the red shadow value, the Black Input Slider is moved to the right while holding down the Alt key. As soon as the slider is clicked, the image will turn red. As the slider is moved to the right, parts of the image will start to change colors. The parts of the image that have changed color are being clipped. When the image begins to show detail getting clipped, the slider should be moved back a bit until only pure red (with no detail) is left visible. Figure 29 shows the Levels Dialogue Box with the Black Input Slider at the selected point. Figure 30 shows the how the image is displayed with the Alt key held down.

Figure 29: Levels' Red Channel with the Black Input Slider Moved to the Right

Figure 30: Image with the Black Input Slider Moved to the Right, in the Red Channel, While Holding Down the Alt Key

To set the red highlight value, the White Input Slider is moved to the left while holding down the Alt Key. Initially, the image will turn black. When the image begins to show detail getting clipped, the slider should be moved back a bit until only the pure whites (with no detail) are left visible. For this image, the red highlights are already slightly clipped, so the White Input Slider will be left at 255. Figure 31 shows the Levels Dialogue Box with the White Input Slider at the selected point. Figure 32 shows the how the image is displayed with the Alt key held down.

Figure 31: Levels' Red Channel with the White Input Slider Left in the Rightmost Position

Figure 32: Image with the White Input Slider Left in the Rightmost Position, in the Red Channel, While Holding Down the Alt Key

The green and blue channels are edited in the same manner. Figures 33 -- 40 show the green and blue channels in Levels after editing.

Figure 33: Levels' Green Channel with the Black Input Slider Moved to the Right

Figure 34: Image with the Black Input Slider Moved to the Right, in the Green Channel, While Holding Down the Alt Key

Figure 35: Levels' Green Channel with the White Input Slider Moved to the Left

Figure 36: Image with the White Input Slider Moved to the Left, in the Green Channel, While Holding Down the Alt Key

Figure 37: Levels' Blue Channel with the Black Input Slider Moved to the Right

Figure 38: Image with the Black Input Slider Moved to the Right, in the Blue Channel, While Holding Down the Alt Key

Figure 39: Levels' Blue Channel with the White Input Slider Moved to the Left

Figure 40: Image with the White Input Slider Moved to the Left, in the Blue Channel, While Holding Down the Alt Key

Figure 41 shows the Histogram after all the shadow and highlight values have been set.

Figure 41: Histogram with Color Channels after Editing

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.

Figure 42: Gamma Input Slider in RGB Channel for Setting the Midtone Contrast

Figures 43 and 44 show the original image and the image after all the adjustments were finalized.

Figure 43: Original Image

Figure 44: Image after All Adjustments were Finalized

There is one caveat with this technique; it is very easy to end up with color casts when setting the shadow and highlight values by using the individual color channels. I recommend this approach only for individuals that are very experienced in image editing.