Advanced color correction with Camera Raw

Header_BeforeandAfterPhotoshop

In a previous article “YOUR FIRST TOUR WITH ADOBE CAMERA RAW“, were the first steps to use Camera Raw, it is a plug-in Adobe Photoshop. In this article we will learn in detail this tool in which regards to advanced color correction.

The following topics are going to be mentioned through this tutorial:

  • Camera raw controls
  • Histogram and RGB levels
  • Preview highlight and shadow clipping
  • Fine-tune tone curves

CAMERA RAW CONTROLS

You must have a previous knowledge of Adobe Camera Raw parameters, in order to know when to use them, since they change in comparison to other tools inside Phtoshop.

  • Zoom tool. Sets the preview zoom to the next preset zoom value when you click within the preview image. Alt-click (Option-click in Mac OS) to zoom out. Drag the Zoom tool in the preview image to zoom in on a selected area. To  return to 100%, double-click the Zoom tool.
  • Hand tool. Moves the image in the preview window if the preview image is set at a zoom level higher than 100%. Hold  down the spacebar to access the Hand tool while using another tool. Double-click the Hand tool to fit the preview image  in the window.
  • White Balance tool. Sets the area you click to a neutral gray tone to remove color casts and adjust the color of the entire image. The Temperature and Tint values change to reflect the color adjustment.
  • Crop tool. Removes part of an image. Drag the tool within the preview image to select the portion you want to keep, and then press Enter.
  • Straighten tool. You can use the Straighten tool to realign an image vertically or horizontally. This tool also resizes or crops the canvas to accommodate straightening the image.
  • Red Eye removal. Removes red eye in flash photos of people and green or white eye in pets.
  • Open Preferences. dialog Opens the Camera Raw Preferences dialog.
  • Rotate buttons. Rotates the photo either counterclockwise or clockwise.

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HISTOGRAM AND RGB LEVELS

The histogram is a representation of the number of pixels at each luminance value in an image. Non-zero 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; while a histogram with a spike at the left side indicates shadow clipping, on the right side indicates highlight clipping.

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.

01AdvancedColorCorrectionCameraRaw

The RGB values of the pixel under the pointer (in the preview image) appear below the histogram.

You can also use the COLOR SAMPLER TOOL (S)  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.

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PREVIEW HIGHLIGHT AND SHADOW CLIPPING

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.

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  • 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 Exposureand Recoverysliders, 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).

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FINE-TUNE TONE CURVES

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.

To adjust tone curves, do any of the following:

  • Drag the Highlights, Lights, Darks, or Shadowsslider 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.

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  • 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.

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  • 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.

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REFERENCES

  1. ADOBE (2013), ADOBE PHOTOSHOP Help and tutorials, link [https://helpx.adobe.com/pdf/photoshop-elements_reference.pdf] visited as of 2015-06-21.
  2. ADOBE (2014), Adobe® Photoshop® CC Help, link [https://helpx.adobe.com/pdf/photoshop_reference.pdf] visited as of 2015-06-21.

 

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