Adjusting Luminance


In traditional analog photography, image color and contrast were controlled through specialized processing and the use of filters. In the digital world, you can make the same adjustments with software. An adjustment can be a way of giving a special, stylized "look" to a final image, oras in the case of our Grande imagesadjustments can be a way to simply make the image true to the photographer's vision of the shot.

Making Shadows Darker

Let's make some adjustments to the tropical hero image first, starting with adjusting the shadow areas to give the image a little more punch.

1.

Press the H key.

The Adjustments HUD appears. This floating Adjustments HUD offers the same controls as the Adjustments Inspector you used in Lesson 4.

Note

The position and options that are open in your Adjustments HUD may be different from what appear in the screen shots on the following pages, depending on which options you used in previous lessons.

2.

Drag the Adjustments HUD to the upper right and make sure it does not cover the image.

Let's start by adjusting the overall luminance of the image in order to darken the shadows. We can achieve this by using the Levels controls in the Adjustments HUD.

3.

Click the disclosure triangle next to Levels to reveal the Levels controls if they are not already visible.

4.

Choose Show Color Value and Show Histogram from the Adjustments HUD Action pop-up menu if the color values and histogram are not visible.

Because the Levels controls are directly below the main histogram, it will be easy to see the effects of the adjustment you are about to make.

5.

Reduce the size of Adjustments HUD by dragging the lower right corner and then use the scroller so that all you can see in the HUD are the Levels controls group and the main histogram.

6.

Click the Quarter-Tone Controls button to activate the Levels quarter-tone controls. The Levels histogram updates with new controls for adjusting four discrete tonal ranges of the image, from black to white, allowing you to make finer adjustments.

7.

Choose Luminance from the Channel pop-up menu, then select the checkbox next to Levels.

The Levels histogram will now display the Luminance channel, which contains the average of the brightest RGB values in the image. The Levels histogram will now also match the main histogram as we make changes.

8.

Drag the leftmost control under the Levels histogram to the right until the B (black point) value is 0.05.

As you drag the black-point control, the Adjustments HUD histogram updates to show the results of the change. The controls under the Levels histogram correspond to the source values. Dragging the black point to the right darkens the shadow areas: The overall image is slightly darkened, but the lower values are affected more. The adjustment results in darker shadows that give the image more depth, but the adjustment also darkens the model's skin tone.

9.

Place the cursor over the model's left cheek and look at the RGB values above the main histogram.

The L (luminance) value should be approximately 146, which is low (dark) for this model. Her fair skin should have a luminance value of around 160 on her cheek. The numbers should confirm what you can already see in the image. Let's brighten the model's skin tones next.

Making Skin Tone Lighter

The model's skin should be glowing. For a photographer, glowing skin equates to specific luminance values. The luminance values for the skin tone of this model's cheek should be somewhere in the 155 to 160 range. So now we'll look at the skin tones to evaluate the levels, then adjust the midtones to match our target range of 155 to 160. But first, let's resize the Adjustments HUD.

1.

Drag the lower right corner of the Adjustments HUD to enlarge it and then click the disclosure triangle for the Exposure controls group. Click the Tint disclosure triangle within the Exposure controls group.

2.

Adjust the size of the HUD until both the Exposure and Levels controls groups are visible.

3.

In the Tint controls of the Exposure group, click the White eyedropper button below the rightmost color wheel.

The Loupe appears, allowing you focus on a particular area of the image as you adjust the tint.

The Tint buttons let you choose a neutral value from your image. You can click any of the three buttons since you will be using it only as a guide. You will be using the Tint adjustments later in this lesson; for now you will use the white tint as a guide to view values in the Adjustments HUD histogram.

4.

Position the cursor over the model's left cheek while using the Centered Loupe set to "Focus on Cursor."

A vertical yellow line in the Adjustments HUD histogram indicates the luminance values of the model's cheek. The line is to the right of the second histogram peak, indicating that the model's skin tone is just above midtone. This value of the current skin tone will guide us when we adjust the skin tone using Level controls.

5.

Press Command-` (accent grave) to turn off the Loupe.

6.

In the Levels controls group, Option-drag the center control under the Levels histogram to the right until the value next to the center G (gray) value is 0.56. Drag the top center control to the right until the center line is just to the right of the vertical, crossing over the peak you viewed earlier.

This pushes the destination pointer for the gray-point adjustment over the area where the histogram line appeared when we chose the white tint, thus affecting the skin tone area more heavily. The skin tone ends up with a darker value. As you drag the center control, all three midtone quarter-value lines move in unison; the black point and white point are unaffected.

7.

Position the cursor over the model's left cheek.

The luminance value in the model's cheek now falls in the 155160 range that the photographer prefersand as you can see, her skin tone is much brighter. Next, let's adjust the color to fit the photographer's vision.




Apple Pro Training Series(c) Aperture 1.5
Apple Pro Training Series: Aperture 1.5
ISBN: 0321496620
EAN: 2147483647
Year: 2007
Pages: 190

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