Tuesday, June 5, 2012

Color Adjustments

 http://help.adobe.com/en_US/photoshop/cs/using/WSfd1234e1c4b69f30ea53e41001031ab64-764fa.html

 Change the color balance using the Photo Filter command

The Photo Filter adjustment mimics the technique of placing a colored filter in front of the camera lens to adjust the color balance and color temperature of the light transmitted through the lens and exposing the film. Photo Filter also lets you choose a color preset to apply a hue adjustment to an image. If you want to apply a custom color adjustment, the Photo Filter adjustment lets you specify a color using the Adobe Color Picker.
  1. Do one of the following:
    • Click the Photo Filter icon  in the Adjustments panel.
    • Choose Layer > New Adjustment Layer > Photo Filter. Click OK in the New Layer dialog box.
    Note: You can also choose Image > Adjustments > Photo Filter. But keep in mind that this method makes direct adjustments to the image layer and discards image information.
  2. In the Adjustments panel, choose the filter color, either a custom filter or a preset. For a custom filter, select the Color option, click the color square, and use the Adobe Color Picker to specify a color for a custom color filter. For a preset filter, select the Filter option and choose one of the following presets from the Filter menu:
    Warming Filter (85 and LBA) and Cooling Filter (80 and LBB)
    Color conversion filters that tune the white balance in an image. If an image was photographed with a lower color temperature of light (yellowish), the Cooling Filter (80) makes the image colors bluer to compensate for the lower color temperature of the ambient light. Conversely, if the photo was taken with a higher color temperature of light (bluish), the Warming Filter (85) makes the image colors warmer to compensate for the higher color temperature of the ambient light.
    Warming Filter (81) and Cooling Filter (82)
    Use light-balancing filters for minor adjustments in the color quality of an image. The Warming Filter (81) makes the image warmer (more yellow), and the Cooling Filter (82) makes the image cooler (bluer).
    Individual Colors
    Apply a hue adjustment to the image depending on the color preset you choose. Your choice of color depends on how you’re using the Photo Filter adjustment. If your photo has a color cast, you can choose a complementary color to neutralize the color cast. You can also apply colors for special color effects or enhancements. For example, the Underwater color simulates the greenish blue color cast in underwater photos.Make sure that Preview is selected to view the results of using a color filter. If you don’t want the image darkened by adding the color filter, be sure that the Preserve Luminosity option is selected.
  3. To adjust the amount of color applied to the image, use the Density slider or enter a percentage in the Density box. A higher density results in a stronger color adjustment.

Apply the Color Balance adjustment

The Color Balance command changes the overall mixture of colors in an image for generalized color correction.
  1. Make sure that the composite channel is selected in the Channels panel. This command is available only when you’re viewing the composite channel.
  2. Do one of the following:
    • Click the Color Balance icon  in the Adjustments panel.
    • Choose Layer > New Adjustment Layer > Color Balance. Click OK in the New Layer dialog box.
    Note: You can also choose Image > Adjustments > Color Balance. But keep in mind that this method makes direct adjustments to the image layer and discards image information.
  3. In the Adjustments panel, select Shadows, Midtones, or Highlights to select the tonal range in which you want to focus the changes.
  4. (Optional) Select Preserve Luminosity to prevent changing the luminosity values in the image while changing the color. This option maintains the tonal balance in the image.
  5. Drag a slider toward a color that you want to increase in the image; drag a slider away from a color that you want to decrease in the image. The values above the color bars show the color changes for the red, green, and blue channels. (For Lab images, the values are for the A and B channels.) Values can range from ‑100 to +100.

Apply the Brightness/Contrast adjustment

The Brightness/Contrast adjustment lets you make simple adjustments to the tonal range of an image. Moving the brightness slider to the right increases tonal values and expands image highlights, to the left decreases values and expands shadows. The contrast slider expands or shrinks the overall range of tonal values in the image.
In normal mode, Brightness/Contrast applies proportionate (nonlinear) adjustments to image layer, as with Levels and Curves adjustments. When Use Legacy is selected, Brightness/Contrast simply shifts all pixel values higher or lower when adjusting brightness. Since this can cause clipping or loss of image detail in highlight or shadow areas, using Brightness/Contrast in Legacy mode is not recommended for photographic images (but can be useful for editing masks or scientific imagery).
Note: Use Legacy is automatically selected when editing Brightness/Contrast adjustment layers created with previous versions of Photoshop.
  1. Do one of the following:
    • Click the Brightness/Contrast icon  in the Adjustments panel.
    • Choose Layer > New Adjustment Layer > Brightness/Contrast. Click OK in the New Layer dialog box.
    Note: You can also choose Image > Adjustments > Brightness/Contrast. But keep in mind that this method makes direct adjustments to the image layer and discards image information.
  2. In the Adjustments panel, drag the sliders to adjust the brightness and contrast. Dragging to the left decreases the level, and dragging to the right increases it. The number at the right of each slider reflects the brightness or contrast value. Values can range from ‑150 to +150 for Brightness, ‑50 to +100 for Contrast.

Adjust black and white points with the Auto option

The Auto option for Levels and Curves and the Auto Tone command automatically adjust the black point and white point in an image. This clips a portion of the shadows and highlights in each channel and maps the lightest and darkest pixels in each color channel to pure white (level 255) and pure black (level 0). The intermediate pixel values are redistributed proportionately. As a result, using the Auto option or Auto Tone increases the contrast in an image because the pixel values are expanded. Because the Auto option and Auto Tone adjust each color channel individually, it may remove color or introduce color casts.
The Auto option and Auto Tone give good results in certain images with an average distribution of pixel values that need a simple increase in contrast.
By default, the Auto option and the Auto Tone command clip the white and black pixels by 0.1%—that is, it ignores the first 0.1% of either extreme when identifying the lightest and darkest pixels in the image. The default settings for the Auto option can be changed in the Auto Color Correction Options dialog box.
  1. Do one of the following:
    • Click the Levels or Curves icon in the Adjustments panel.
    • Choose Layer > New Adjustment Layer and choose either Levels or Curves. Click OK in the New Layer dialog box.
    Note: You can choose Image > Auto Tone to apply the adjustment directly to the image layer. Keep in mind that this method discards image information and is automatic. You cannot adjust any of the options in the following steps.
  2. In the Adjustments panel, Alt-click (Windows) or Option-click (Mac OS) the Auto button.
  3. Under Algorithms in the Auto Color Correction Options dialog box, select Enhance Per Channel Contrast.
  4. Adjust the amount of shadow and highlight values that are clipped, and adjust the target color for the midtones.
  5. Click OK to apply the Auto option settings.

Apply the Auto Contrast adjustment

The Auto Contrast command adjusts image contrast automatically. Because Auto Contrast does not adjust channels individually, it does not introduce or remove color casts. It clips the shadow and highlight values in an image and then maps the remaining lightest and darkest pixels in the image to pure white (level 255) and pure black (level 0). This makes the highlights appear lighter and shadows appear darker.
By default, when identifying the lightest and darkest pixels in an image, Auto Contrast clips the white and black pixels by 0.5%—that is, it ignores the first 0.5% of either extreme. You can change this default using the Auto Color Correction Options found in the Levels and the Curves dialog boxes.
Auto Contrast can improve the appearance of many photographic or continuous-tone images. It does not improve flat‑color images.
  1. Do one of the following:
    • Click the Levels or Curves icon in the Adjustments panel.
    • Choose Layer > New Adjustment Layer and choose either Levels or Curves. Click OK in the New Layer dialog box.
    Note: You can also choose Image > Auto Contrast to apply the adjustment directly to the image layer. Keep in mind that this method discards image information and its application is automatic. You cannot adjust any of the options in the following steps.
  2. In the Adjustments panel, Alt-click (Windows) or Option-click (Mac OS) the Auto button.
  3. Under Algorithms in the Auto Color Correction Options dialog box, select the Enhance Monochromatic Contrast option.
  4. Specify the shadows and highlights that are clipped, and adjust the target color for the midtones.
  5. Click OK to apply Auto Contrast.

Remove a color cast using Auto Color

Auto Color adjusts the contrast and color of an image by searching the image to identify shadows, midtones, and highlights. By default, Auto Color neutralizes the midtones using a target color of RGB 128 gray and clips the shadows and highlight pixels by 0.5%. You can change these defaults in the Auto Color Correction Options dialog box.
  1. Do one of the following:
    • Click the Levels or Curves icon in the Adjustments panel.
    • Choose Layer > New Adjustment Layer and choose either Levels or Curves. Click OK in the New Layer dialog box.
    Note: You can also choose Image > Auto Color to apply the adjustment directly to the image layer. Keep in mind that this method discards image information and is automatic. You cannot adjust any of the options in the following steps.
  2. In the Adjustments panel, Alt-click (Windows) or Option-click (Mac OS) the Auto button.
  3. Under Algorithms in the Auto Color Correction Options dialog box, select the Find Dark & Light colors option.
  4. Select the Snap Neutral Midtones option.
  5. Specify the shadows and highlights that are clipped, and adjust the target color for the midtones.
  6. Click OK to apply Auto Color.

Set Auto adjustment options

The Auto Color Correction options control the automatic tone and color corrections available in both Levels and Curves. It also controls the settings for the Auto Tone, Auto Contrast, and Auto Color commands. The Auto Color Correction options let you specify shadow and highlight clipping percentages, and assign color values to shadows, midtones, and highlights.
You can apply the settings during a single use of the Levels or Curves adjustment, or you can save the settings as default values when applying Auto Tone, Auto Contrast, Auto Color, and the Auto option for Levels and Curves.
Auto Color Correction Options dialog box
A.
Auto Contrast option
B.
Auto Levels option
C.
Auto Color option
D.
Set target colors, black point, and white point
  1. Click the Levels or Curves icon in the Adjustments panel.
  2. Alt-click (Windows) or Option-click (Mac OS) the Auto button in the Adjustments panel.
  3. Specify the algorithm you want Photoshop to use to adjust the overall tonal range of an image:
    Enhance Monochromatic Contrast
    Clips all channels identically. This preserves the overall color relationship while making highlights appear lighter and shadows appear darker. The Auto Contrast command uses this algorithm.
    Enhance Per Channel Contrast
    Maximizes the tonal range in each channel to produce a more dramatic correction. Because each channel is adjusted individually, Enhance Per Channel Contrast may remove or introduce color casts. The Auto Tone command uses this algorithm.
    Find Dark & Light Colors
    Finds the average lightest and darkest pixels in an image and uses them to maximize contrast while minimizing clipping. The Auto Color command uses this algorithm.
  4. Select Snap Neutral Midtones if you want Photoshop to find an average nearly-neutral color in an image and then adjust the gamma (midtone) values to make the color neutral. The Auto Color command uses this algorithm.
  5. To specify how much to clip black and white pixels, enter percentages in the Clip text boxes. A value between 0.0% and 1% is recommended. By default, Photoshop clips the black and white pixels by 0.1%—that is, it ignores the first 0.1% of either extreme when identifying the lightest and darkest pixels in the image. Because of the better output quality of modern scanners and digital cameras, these default clipping percentages might be too high.
  6. To assign (target) color values to the darkest, neutral, and lightest areas of an image, click a color swatch.
  7. Do one of the following:
    • To use the settings in the current Levels or Curves adjustment, click OK. If you then click the Auto button, Photoshop reapplies the same settings to the image.
    • To save the settings as the default, select Save as Defaults, and then click OK. The next time you access Levels or Curves in the Adjustments panel, you can apply the same setting by clicking the Auto button. The Auto Tone, Auto Contrast, and Auto Color commands also use the default clipping percentages.
    Note: When you save the Auto Color Correction options as defaults for Auto Color, Auto Tone, and Auto Contrast, it does not matter what algorithm you select in step 2. The three auto-correction commands use only those values that you set for the target colors and clipping. The only exception is that the Auto Color command also uses the Snap Neutral Midtones option.

Apply the Variations command

The Variations command lets you adjust the color balance, contrast, and saturation of an image by showing you thumbnails of alternatives. This command is most useful for average-key images that don’t require precise color adjustments.
Note: The Variations command is unavailable for indexed-color images, 16-bit images, and 64-bit versions of Mac OS.
  1. Choose Image > Adjustments > Variations. The two thumbnails at the top of the dialog box show the original selection (Original) and the selection with its currently selected adjustments (Current Pick). When you first open the dialog box, these two images are the same. As you make adjustments, the Current Pick image changes to reflect your choices.
  2. Select the Show Clipping option if you want to display a preview of areas in the image that are clipped—converted to pure white or pure black—by the adjustment. Clipping can result in undesirable color shifts, as distinct colors in the original image are mapped to the same color. Clipping does not occur when you adjust midtones.
  3. Select what to adjust in the image:
    Shadows, Midtones, or Highlights
    Adjusts the dark, middle, or light areas.
    Saturation
    Changes the degree of hue in the image. If you exceed the maximum saturation for a color, it may be clipped.
  4. Drag the Fine/Coarse slider to determine the amount of each adjustment. Moving the slider one tick mark doubles the adjustment amount.
  5. Adjust the color and brightness:
    • To add a color to the image, click the appropriate color thumbnail.
    • To subtract a color, click the thumbnail for its opposite color. For example, to subtract cyan, click the More Red thumbnail. See Understanding color.
    • To adjust brightness, click a thumbnail on the right side of the dialog box.
    The effects of clicking the thumbnails are cumulative. For example, clicking the More Red thumbnail twice applies the adjustment twice. Each time you click a thumbnail, the other thumbnails change. The three Current Pick thumbnails always reflect the current choices.
    You can also save the settings you make in the Variations dialog box for reuse on other images. For more information on saving and loading settings, see Save adjustment settings and Reapply adjustment settings.

Using the Equalize command

The Equalize command redistributes the brightness values of the pixels in an image so that they more evenly represent the entire range of brightness levels. Equalize remaps pixel values in the composite image so that the brightest value represents white, the darkest value represents black, and intermediate values are evenly distributed throughout the grayscale.
You can use the Equalize command when a scanned image appears darker than the original and you want to balance the values to produce a lighter image. Using Equalize together with the Histogram panel lets you see before-and-after brightness comparisons.
  1. (Optional) Select an area of the image to equalize.
  2. Choose Image > Adjustments > Equalize.
  3. If you selected an area of the image, select what to equalize in the dialog box, and click OK:
    Equalize Selected Area Only
    Evenly distributes only the pixels in the selection.
    Equalize Entire Image Based On Selected Area
    Evenly distributes all image layers based on those in the selection.
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