Levels in Photoshop -- Part IV

Article and Photography by Ron Bigelow

www.ronbigelow.com

Photoshop CS or Photoshop CS2 Used in this Tutorial

Setting Custom White Balance.

With a little preplanning, Levels can be used to perform a custom white balance. All that is required is that the photographer shoot a neutral gray object (e.g., a gray card) in the same lighting conditions as the regular shots. If shooting JPEG, the camera needs to be set to one of the preset white balance options (e.g., daylight or cloudy) for both shots (do not use auto white balance). If the image is converted from a raw file, the white balance settings in the raw converter need to be the same for both the regular and gray card images (to make it easier on yourself, I suggest that a preset white balance setting be used even with raw when you plan to use Levels to set the white balance).

Figure 1: Image that Needs a Custom White Balance

Figure 1 shows an image that was shot in late evening light. This is a tough image for the camera to determine the proper white balance. The image has a heavy preponderance of one color, and the light was a mixture of overhead, direct, and reflected light (each with its own color temperature). To insure proper white balance, a gray card was shot right after the flower was photographed (see Figure 2).

Figure 2: Gray Card
To perform a custom white balance, both images are opened in Photoshop. The images are arranged in a way that both can be seen (see Figure 3).
Figure 3: Both Images Opened in the Image Editing Program
Figure 4: Levels with Gray Eyedropper
The flower image is selected. Levels is launched and the Gray Eyedropper is double clicked (see Figure 4).
Figure 5: Color Picker Dialog Box for Selecting the Gray Color

The Color Picker dialog box appears as shown in Figure 5. This Color Picker is used to set the gray values. These values will then be assigned to whatever point is clicked with the Gray Eyedropper. The values are set by entering the values directly into the R, G, and B boxes. Since a neutral point is going to be identified, all of the values should be equal. It is necessary to match these values to the gray object that was photographed. For most neutral gray objects, values of 128, 128, and 128 will be appropriate. Clicking OK closes the Color Picker.

The last step is to click the Gray Eyedropper on the gray card image as shown in Figure 6). The flower image is now custom white balanced.

Figure 6: Performing a Custom White Balance
Figure 7 and 8 show the original and custom white balanced images.
Figure 7: Original Image
Figure 8: Image after Custom White Balance

Preparing for Printing

Figure 9: Levels with Output Levels and Output Sliders

The last couple of items on the Levels dialog box are the Output Levels and the Output Sliders. These are shown in Figure 9. The Output Levels show the values for two items. The left value shows the darkest tonal value that the image contains (i.e., if a value of 5 is shown in this box, the darkest tone in the image will be mapped to a value of 5). The right value shows the lightest tonal value that the image contains (i.e., if a value of 245 is shown in this box, the lightest tone in the image will be mapped to a value of 245). Directly below Output Levels are two sliders. The left slider is the Black Output Slider and is used to set the darkest tone in the image. The right slider is the White Output Slider and is used to set the lightest tone in the image. Moving the Black and White Output Sliders inward decreases the contrast of the image. As these two sliders are moved, the values in the corresponding Output Levels boxes will change.

It can be easy to get the Input and Output Sliders confused. To help clarify the issue, Table 1 compares the action of the Black Input Slider vs. the Black Output Slider and the White Input Slider vs. the White Output Slider. As shown in the table, if the Black Input Slider is set to ten, a tonal value of ten will be changed to zero. In other words, the tonal value of ten will be changed to black. In fact, everything between zero and ten will be black. This makes the darker tones even darker. Unfortunately, those tones that become black are clipped. On the other hand, if the Black Output Slider is set to ten, a tonal value of zero will be changed to ten. In other words, what used to be black will now be dark gray. This makes the dark tones lighter, but it does not clip any data.

As shown in the lower half of Table 1, if the White Input Slider is set to 245, a tonal value of 245 will be changed to 255. Thus, the tonal value of 245 will be changed to white. In fact, everything between 245 and 255 will be white. This makes the lighter tones even lighter. Unfortunately, those tones that become white are clipped. When the White Output Slider is set to 245, a tonal value of 255 will be changed to 245. In other words, what used to be white will now be light gray. This makes the light tones darker, but it does not clip any data.

In short, when the Input Sliders are moved inward, the contrast is increased by stretching the tonal values. When the Output Sliders are moved inward, the contrast is decreased by compressing the tonal values. The main purpose of the Output Sliders is to allow the normal, tonal range of an image (i.e., 0 -- 255) to be compressed into a smaller range (10 -- 245 in the example in Table 1).

Table 1: Input Sliders Vs Output Sliders
Black Sliders
Slider
Slider Value
Action
Comments
Black Input Slider
10
Maps a value of ten to a value of zero. Maps the slider value to a value of zero, making it black. Data will be clipped.
Black Output Slider
10
Maps a value of zero to a value of ten. Maps the value of zero to the slider value. This essentially remaps the black point making it lighter. Data is not clipped.
 
White Sliders
Slider
Slider Value
Action
Comments
White Input Slider
245
Maps a value of 245 to a value of 255. Maps the slider value to a value of 255, making it white. Data will be clipped.
White Output Slider
245
Maps a value of 255 to a value of 245 Maps the value of 255 to the slider value. This essentially remaps the white point making it darker. Data is not clipped.
Figure 10: Levels with Output Slider Adjustments
Table 10 shows the Levels dialog box after the Output Sliders have been adjusted. Figures 11 and 12 show the image before and after the Output Slider adjustments. Without a doubt, the image with the Output Slider adjustments has less contrast.
Figure 11: Original Image
Figure 12: Image after Output Slider Adjustments

So, the big question is, "Why would anyone go to all the trouble of adjusting the Output Sliders only to end up with an image that has less contrast?" The answer is: when they are targeting an image for a specific printer or printing press.

Not all printers and printing presses can print smoothly from pure black to pure white. For instance, as a printer prints progressively darker tones, it lays down more and/or larger dots of ink. However, if the resolution of the printer is not high enough, a point may be reached where the printer does not have enough fine control to differentiate between the darkest tones. When this happens, all of the tones beyond that point will turn to black in the print. As an example, a specific printer may not be able to differentiate between tones with a value lower than ten. If an image were printed without Output Slider adjustment, the tones from zero to ten would all be black. The detail in the image between these tonal values would be lost during the printing process -- these tones would be clipped. However, if the Black Output Slider is moved to a value of ten, the printer will be able to handle all of the darker tones (the darker tones will have been mapped to values that the printer can handle), and no tones will be clipped during the printing process.

On the highlight side, as a printer prints progressively lighter tones, it lays down less and/or smaller dots of ink. However, if the resolution of the printer is not high enough, a point may be reached where the printer does not have enough fine control to differentiate between the lightest tones (the printer can not make the dots any smaller or fewer). When this happens, all of the tones beyond that point will turn to the white of the paper. As an example, a specific printer may not be able to differentiate between tones with a value higher than 245. If an image were printed without Output Slider adjustment, the tones from 245 to 255 would all be white. The detail in the image between these tonal values would be lost during the printing process -- these tones would be clipped. However, if the White Output Slider is moved to a value of 245, the printer will be able to handle all of the lighter tones (the lighter tones will have been mapped to values that the printer can handle), and no tones will be clipped during the printing process.

Now, there are three caveats that need to be kept in mind when considering this approach for targeting. First, once the Output Sliders have been adjusted for a particular printer, that image should not be used to print to anther printer with different printer characteristics. The Output Slider settings are particular to a specific printer and will likely cause problems if used on another printer. Second, if an image has specular highlights, using the White Output Slider to target an image for a printer becomes trickier and requires more skill from the photographer. Third, using the Output Sliders to make adjustments for a printer is not necessarily the best method available. Using an ICC profile for a printer and choosing Black Point Compensation during the conversion from the image color space to the printer color space should take care of this issue without requiring the use of the Output Sliders.

Articles

Levels -- Part III