A histogram is a representation of the number of pixels at each luminance value in an image. A histogram that has nonzero values for each luminance value indicates an image that takes advantage of the full tonal scale. A histogram that doesn’t use the full tonal range corresponds to a dull image that lacks contrast. A histogram with a spike at the left side indicates shadow clipping; a histogram with a spike on the right side indicates highlight clipping.
Select Shadows or Highlights to see in the preview image which pixels are being clipped. For more information, see Preview highlight and shadow clipping in Camera Raw.
One common task for adjusting an image is to spread out the pixel values more evenly from left to right on the histogram, instead of having them bunched up at one end or the other.
A histogram is made up of three layers of color that represent the red, green, and blue color channels. White appears when all three channels overlap. Yellow, magenta, and cyan appear when two of the RGB channels overlap (yellow equals the red + green channels, magenta equals the red + blue channels, and cyan equals the green + blue channels).
The histogram changes automatically as you adjust the settings in the Camera Raw dialog box.
The RGB values of the pixel under the pointer (in the preview image) appear below the histogram.
Note:
You can also use the Color Sampler tool 
to place up to nine color samplers in the preview image. The RGB values appear above the preview image. To remove a color sampler, Alt-click (Windows) or Option-click (Mac OS) it. To clear the color samplers, click Clear Samplers.
The Camera Raw dialog box displays the RGB values of the pixel under the pointer.
Clipping occurs when the color values of a pixel are higher than the highest value or lower than the lowest value that can be represented in the image. Over bright values are clipped to output white, and over dark values are clipped to output black. The result is a loss of image detail.
- To see which pixels are being clipped with the rest of the preview image, select Shadows or Highlights options at the top of the histogram. Or press U to see shadow clipping, O to see highlight clipping.
- To see only the pixels that are being clipped, press Alt (Windows) or Option (Mac OS) while dragging the Exposure, Recovery, or Blacks sliders.
For the Exposure and Recovery sliders, the image turns black, and clipped areas appear white. For the Blacks slider, the image turns white and clipped areas appear black. Colored areas indicate clipping in one color channel (red, green, blue) or two color channels (cyan, magenta, yellow).
Note:
In some cases, clipping occurs because the color space that you are working in has a gamut that is too small. If your colors are being clipped, consider working in a color space with a large gamut, such as ProPhoto RGB.
To adjust the white balance, identify which objects in the image you want to be neutral-colored (white or gray), and then adjust the colors to make those objects neutral. A white or gray object in a scene takes on the color cast by the ambient light or flash used to shoot the picture. When you use the White Balance tool 
to specify an object that you want white or gray, Camera Raw can determine the color of the light in which the scene was shot and then adjust for scene lighting automatically.
Color temperature (in Kelvins) is used as a measure of scene lighting. Natural and incandescent light sources give off light in a predictable distribution according to their temperature.
A digital camera records the white balance at the time of exposure as a metadata entry. The Camera Raw plug-in reads this value and makes it the initial setting when you open the file in the Camera Raw dialog box. This setting usually yields the correct color temperature, or nearly so. You can adjust the white balance if it is not right.
Note:
Not all color casts are a result of incorrect white balance. Use the DNG Profile Editor to correct a color cast that remains after the white balance is adjusted. See Adjust color rendering for your camera in Camera Raw.
The Basic tab in the Camera Raw dialog box has three controls for correcting a color cast in an image:
White Balance
Camera Raw applies the white balance setting and changes the Temperature and Tint properties in the Basic tab accordingly. Use these controls to fine-tune the color balance.
Camera raw and DNG files also have the following white balance settings: Daylight, Cloudy, Shade, Tungsten, Fluorescent, and Flash.
Note:
If Camera Raw doesn’t recognize the white balance setting of a camera, choosing As Shot is the same as choosing Auto.
Temperature
Sets the white balance to a custom color temperature. Decrease Temperature to correct a photo taken with a lower color temperature of light; the Camera Raw plug-in makes the image colors bluer to compensate for the lower color temperature (yellowish) of the ambient light. Conversely, increase Temperature to correct a photo taken with a higher color temperature of light; the image colors become warmer (yellowish) to compensate for the higher color temperature (bluish) of the ambient light.
Note:
The range and units for the Temperature and Tint controls are different when you are adjusting a TIFF or JPEG image. For example, Camera Raw provides a true-temperature adjustment slider for raw files from 2,000 Kelvin to 50,000 Kelvin. For JPEG or TIFF files, Camera Raw attempts to approximate a different color temperature or white balance. Because the original value was already used to alter the pixel data in the file, Camera Raw does not provide the true Kelvin temperature scale. In these instances, an approximate scale of -100 to 100 is used in place of the temperature scale.
Correcting the white balance
A. Moving the Temperature slider to the right corrects a photo taken with a higher color temperature of light B. Moving the Temperature slider to the left corrects a photo taken with a lower color temperature of light C. Photo after color temperature adjustment
Tint
Sets the white balance to compensate for a green or magenta tint. Decrease Tint to add green to the image; increase Tint to add magenta.
To adjust the white balance quickly, select the White Balance tool and then click an area in the image that you want to be a neutral gray. The Temperature and Tint properties adjust to make the selected color exactly neutral (if possible). If you’re clicking whites, choose a highlight area that contains significant white detail rather than a specular highlight. You can double-click theWhite Balance tool to reset White Balance to As Shot.
You adjust the image tonal scale using the tone controls in the Basic tab.
When you click Auto at the top of the tone controls section of the Basic tab, Camera Raw analyzes the image and makes automatic adjustments to the tone controls.
You can also apply automatic settings separately for individual tone controls. To apply an automatic adjustment to an individual tone control, such as Exposure or Contrast, press Shift and double-click the slider. To return an individual tone control to its original value, double-click its slider.
When you adjust tone automatically, Camera Raw ignores any adjustments previously made in other tabs (such as fine-tuning of tone in the Tone Curves tab). For this reason, apply automatic tone adjustments first—if at all—to get an initial approximation of the best settings for your image. If you are careful during shooting and have deliberately shot with different exposures, you probably don’t want to undo that work by applying automatic tone adjustments. On the other hand, you can always try clicking Auto and then undo the adjustments if you don’t like them.
Previews in Adobe® Bridge use the default image settings. If you want the default image settings to include automatic tone adjustments, select Apply Auto Tone Adjustments in the Default Image settings section of the Camera Raw preferences.
Note:
If you are comparing images based on their previews in Adobe Bridge, leave the Apply Auto Tone Adjustments preference deselected, which is the default. Otherwise, you’ll be comparing images that have already been adjusted.
As you make adjustments, keep an eye on the end points of the histogram, or use the shadow and highlight clipping previews.
While moving the tone controls sliders, hold down Alt (Windows) or Option (Mac OS) to preview where highlights or shadows are clipped. Move the slider until clipping begins, and then reverse the adjustment slightly. (For more information, see Preview highlight and shadow clipping in Camera Raw.)
- To manually adjust a tone control, drag the slider, type a number in the box, or select the value in the box and press the Up or Down arrow key.
- To reset a value to its default, double-click the slider control.
Note:
The tone controls that appear in the Basic panel depend on whether you are working in Process Version PV2012, PV2010, or PV2003, as noted.
Exposure (All)
Adjusts the overall image brightness. Adjust the slider until the photo looks good and the image is the desired brightness. Exposure values are in increments equivalent to aperture values (f‑stops) on a camera. An adjustment of +1.00 is similar to opening the aperture 1 stop. Similarly, an adjustment of ‑1.00 is like closing the aperture 1 stop.
Contrast (All)
Increases or decreases image contrast, mainly affecting midtones. When you increase contrast, the middle-to-dark image areas become darker, and the middle-to-light image areas become lighter. The image tones are inversely affected as you decrease contrast.
Highlights (PV2012)
Adjusts bright image areas. Drag to the left to darken highlights and recover “blown out” highlight details. Drag to the right to brighten highlights while minimizing clipping.
Shadows (PV2012)
Adjusts dark image areas. Drag to the left to darken shadows while minimizing clipping. Drag to the right to brighten shadows and recover shadow details.
Whites (PV2012)
Adjusts white clipping. Drag to the left to reduce clipping in highlights. Drag to the right to increase highlight clipping. (Increased clipping may be desirable for specular highlights, such as metallic surfaces.)
Blacks (PV2012)
Adjusts black clipping. Drag to the left to increase black clipping (map more shadows to pure black). Drag to the right to reduce shadow clipping.
Blacks (PV2010 and PV2003)
Specifies which image values map to black. Moving the slider to the right increases the areas that become black, sometimes creating the impression of increased image contrast. The greatest effect is in the shadows, with much less change in the midtones and highlights.
Recovery (PV2010 and PV2003)
Attempts to recover details from highlights. Camera Raw can reconstruct some details from areas in which one or two color channels are clipped to white.
Fill Light (PV2010 and PV2003)
Attempts to recover details from shadows, without brightening blacks. Camera Raw can reconstruct some details from areas in which one or two color channels are clipped to black. Using Fill Light is like using the shadows portion of the Photoshop® Shadow/Highlight filter or the After Effects® Shadow/Highlight effect.
Brightness (PV2010 and PV2003)
Adjusts the brightness or darkness of the image, much as the Exposure property does. However, instead of clipping the image in the highlights or shadows, Brightness compresses the highlights and expands the shadows when you move the slider to the right. Often, the best way to use this control is to set the overall tonal scale by first setting Exposure, Recovery, and Blacks; then set Brightness. Large Brightness adjustments can affect shadow or highlight clipping, so you may want to readjust the Exposure, Recovery, or Blacks property after adjusting Brightness.
Learn More: Watch the video tutorial What's New in Camera Raw by Matt Kloskowski. See also, Why You Should Set Photoshop to Open Your JPGs in Adobe Camera RAW - video tutorial by Terry White (8:07).
Use the controls in the Tone Curve tab to fine-tune images after you’ve made tone adjustments in the Basic tab. The tone curves represent changes made to the tonal scale of an image. The horizontal axis represents the original tone values of the image (input values), with black on the left and progressively lighter values toward the right. The vertical axis represents the changed tone values (output values), with black on the bottom and progressing to white at the top.
If a point on the curve moves up, the output is a lighter tone; if it moves down, the output is a darker tone. A straight, 45‑degree line indicates no changes to the tone response curve: the original input values exactly match the output values.
Use the tone curve in the nested Parametric tab to adjust the values in specific tonal ranges in the image. The areas of the curve affected by the region properties (Highlights, Lights, Darks, or Shadows) depend on where you set the split controls at the bottom of the graph. The middle region properties (Darks and Lights) mostly affect the middle region of the curve. The Highlight and Shadows properties mostly affect the ends of the tonal range.
- Drag the Highlights, Lights, Darks, or Shadows slider in the nested Parametric tab. You can expand or contract the curve regions that the sliders affect by dragging the region divider controls along the horizontal axis of the graph.
- Drag a point on the curve in the nested Point tab. As you drag the point, the Input and Output tonal values are displayed beneath the tone curve.
- Choose an option from the Curve menu in the nested Point tab. The setting you choose is reflected in the Point tab, but not in the settings in the Parametric tab. Medium Contrast is the default setting.
- Select the Parametric Curve Targeted Adjustment tool
in the toolbar and drag in the image. The Parametric Curve Targeted Adjustment tool adjusts the Highlights, Lights, Darks, or Shadows curve region based on the values in the image where you click.
Note:
The Targeted Adjustment tool does not affect point curves.
You can change the color saturation of all colors by adjusting the Clarity, Vibrance, and Saturation controls on the Basic tab. (To adjust saturation for a specific range of colors, use the controls on the HSL / Grayscale tab.)
Clarity
Adds depth to an image by increasing local contrast, with greatest effect on the midtones. This setting is like a large-radius unsharp mask. When using this setting, it is best to zoom in to 100% or greater. To maximize the effect, increase the setting until you see halos near the edge details of the image and then reduce the setting slightly.
Vibrance
Adjusts the saturation so that clipping is minimized as colors approach full saturation. This setting changes the saturation of all lower-saturated colors with less effect on the higher-saturated colors. Vibrance also prevents skin tones from becoming oversaturated.
Saturation
Adjusts the saturation of all image colors equally from -100 (monochrome) to +100 (double the saturation).
You can use the controls in the HSL / Grayscale tab to adjust individual color ranges. For example, if a red object looks too vivid and distracting, you can decrease the Reds values in the nested Saturation tab.
The following nested tabs contain controls for adjusting a color component for a specific color range:
Hue
Changes the color. For example, you can change a blue sky (and all other blue objects) from cyan to purple.
Saturation
Changes how vivid or pure the color. For example, you can change a blue sky from gray to highly saturated blue.
Grayscale Mix
Use controls in this tab to specify the contribution of each color range to the grayscale version of the image.
The Targeted Adjustment tool allows you to make tonal and color corrections by dragging directly on a photo. Using the Targeted Adjustment tool, you can drag down on a blue sky to desaturate it, for example, or drag up on a red jacket to intensify its hue.
- To make tone curve adjustments using the Targeted Adjustmenttool, click
it in the toolbar and choose Parametric Curve. Then, drag in the
image.
The Parametric Curve Targeted Adjustment tool adjusts the Highlights, Lights, Darks, or Shadows curve region based on the values in the image where you click.
The keyboard shortcut T toggles the last Targeted Adjustment tool you used.
Use the controls in the Split Toning tab to color a grayscale image. You can add one color throughout the tonal range, such as a sepia appearance, or create a split tone result, in which a different color is applied to the shadows and the highlights. The extreme shadows and highlights remain black and white.
You can also apply special treatments, such as a cross-processed look, to a color image.
In Camera Raw 7.1 or later, you can work with 16-, 24-, and 32-bit floating point images--often referred to as HDR (high dynamic range images). Camera Raw opens TIFF and DNG format HDR images. Make sure that the images are in process version 2012. (See Process Versions.)
You can use the Basic tab controls to edit HDR images. The Basic tab Exposure control has an expanded range when working with HDR images (+10 to -10).
When you are done editing, click Done or Open Image to open the image in Photoshop. The image opens as a 16-bit or 8-bit image, depending on how you have the Workflow Options set.
To open an HDR image in Camera Raw:
Creating and editing HDR images in Photoshop and Lightroom 4.1
Julieanne Kost demonstrates how to create a 32-bit file from multiple exposures in Photoshop and then refine the image's color and tonality in Lightroom 4.1.
For more information about HDR images, see High dynamic range images in Photoshop Help.
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