Dig in to Adobe Camera Raw

The ability to import unprocessed images in their Raw format is what makes Adobe Photoshop CSthe digital photographer's tool of choice. Dig in to its robust features.

Our preferred method for converting RAW captures is the Camera Raw interface in Photoshop (Figure 1). This was offered as an optional plug-in for Photoshop 7.0.1 and is now included as part of Photoshop CS. Camera Raw gives you extensive control over the image conversion and also provides an efficient workflow. To convert RAW files, you simply open them in Photoshop as you would any other image file, and the Camera Raw dialog automatically pops up so you can fine-tune the image adjustments. Note that Camera Raw supports RAW captures for most, but not all, cameras.

Figure 1: Photoshop's Camera Raw interface is our preferred method of converting RAW captures.

Navigation

The navigation controls in Camera Raw provide the same functionality as the Zoom and Hand tools in Photoshop, making it easy to focus on particular areas of the image as you fine-tune the adjustments to be applied in the RAW conversion process. You can double-click the Zoom tool to view the image at 100 percent, and double-click the Hand tool to size the image to fit the window. You can also select a specific zoom setting from the drop-down list at the bottom left of the Camera Raw dialog. It’s important to view the image at 100 percent scale so you can see all the fine detail; this will allow you to make a better decision about the relative merits of the image, in addition to providing an overall look at the complete image.

Histogram

The histogram provides critical information as you adjust the settings in the Camera Raw dialog (Figure 2). Just as the histogram is invaluable when capturing images to ensure proper exposure, the histogram in the Camera Raw dialog is critical for ensuring that you aren’t clipping highlights or shadows. We strongly encourage you to review the histogram as you make adjustments to your images with Camera Raw.

Figure 2: The histogram display in Camera Raw allows you to make more informed adjustments to your images.

In addition to watching the histogram as you adjust your image, you can also use a clipping display for the Exposure and Shadows sliders in the Camera Raw dialog. This allows you to get a much better idea of where you are sacrificing detail in the image based on the adjustments you are making. To get the clipping display, hold the Alt key (Option on Macintosh) while moving the Exposure and Shadow sliders.

White balance

Digital cameras provide a white balance setting to compensate for the color cast created by various types of lighting. For example, incandescent lighting produces a yellow color cast, so the camera will compensate by shifting the color toward blue.

If you used the wrong white balance preset in the camera, you can select another option from the drop-down list. This will change the appearance of the image so that it looks as if you had used that new white balance setting during capture. The default is to leave the settings as they were photographed. Because of the control provided during the conversion, we capture all images with the camera’s automatic white balance setting and then fine-tune them as needed during conversion.

If a white balance preset doesn’t provide the perfect adjustment for the image, you can fine-tune the Temperature and Tint sliders. The Temperature slider controls the overall white balance setting for the image. Moving the slider to the right will give you an image with warmer colors (yellows and reds), as though it had been captured at a higher temperature setting. Moving the slider to the left will produce an image with cooler colors (blues and greens), as though it had been captured at a lower temperature setting. You can also fine-tune the overall color in the image with the Tint slider, which shifts the image between green and magenta.

Tonal and color adjustments

The Camera Raw dialog offers a number of excellent tonal adjustments that let you control the brightness, contrast, and saturation of the final image.

The Exposure adjustment allows you to produce a linear shift in brightness, where all pixels in the image are brightened or darkened to a similar degree. The unit of measure is Exposure Value, which is what photographers would think of as the number of stops of exposure compensation. Because this is a linear adjustment that affects the brightness of all pixels in the image, it’s possible to clip highlights or shadows in your image. It is important to watch the Histogram display as you adjust this setting. You would typically use the Exposure control to adjust images that are significantly over- or underexposed.

The Shadows slider functions the same way the black-point slider in the Levels dialog does. It allows you to define a black point for your image, so that you can maximize contrast in the final image. You can get a preview of where detail is being clipped by holding the Alt (Windows) or Option (Macintosh) key while moving the slider. As you move the slider, you can see which color channels are losing detail based on where the color appears. When black appears, it’s an indication that those areas of the image have been clipped to pure black.

The Brightness slider allows you to adjust the overall brightness of the image, similar to the control provided by the Exposure slider. The only difference is that the Brightness slider will not clip highlights or shadows, but will instead compress the tonal information at the ends of the tonal range as you make adjustments. It’s therefore a safer adjustment tool, although it doesn’t provide the range offered by the Exposure slider. Think of it as behaving like the middle tone slider in the Levels dialog.

The Contrast slider adjusts the contrast in the middle tones of your image. Highlights and shadows will not be clipped by this control except with extreme adjustments.

The Saturation slider allows you to fine-tune the saturation of colors in the image. As with the Hue/Saturation dialog in Photoshop, you shouldn’t increase saturation too much or you’ll produce artificial-looking colors and lose detail in highly saturated areas of the image. In fact, we prefer not to adjust saturation at all in the RAW conversion, leaving those adjustments for Photoshop.

Detail settings

In addition to the tonal and color adjustments, you can adjust detail settings for your images. The Sharpness setting allows you to apply some sharpening to compensate for the loss of sharpness that occurs in the digital capture process. We find that the default value of 25 is excessive for most images. Our preference is to set this to zero and apply our own sharpening using the Unsharp Mask filter.

Luminance Smoothing and Color Noise Reduction both target noise in your image. Luminance Smoothing reduces noise where the variation is monochromatic, and Color Noise Reduction cleans up noise where there are color variations. If you have noise in your images due to a high ISO setting, a long exposure, or other factors, these controls can help minimize that noise. The Color Noise Reduction setting can also be used to minimize moiré patterns, such as those you might capture in finely woven fabric patterns.

Output settings

At the bottom of the Camera Raw dialog are settings that affect the output of the final image file. The Space option allows you to select the color space for the image. We recommend using the Adobe RGB (1998) color space here, as it’s the most appropriate color space for images that will be printed to an inkjet printer.

The Depth drop-down allows you to choose either 8 Bits/Channel or 16 Bits/Channel. We strongly recommend working with 16 Bits/Channel, as it provides the maximum amount of information in the final file. If you immediately convert the image to 8-bit, you are eliminating much of the benefit of capturing in RAW mode to begin with. If you convert the image to a 16-bit file, you will be able to maintain much smoother gradations of tone and color.

The Size option lets you change the size of the image in the conversion process. This may sound like a job for Photoshop’s Image Size dialog, but resizing the image in the RAW conversion will produce better image quality than if you sized the image in Photoshop later. This is because the RAW conversion involves interpolation of the image’s color data—the imaging sensor captures only luminosity values, so color information must be interpolated. If you also interpolate the image to a different size in this process, you maximize quality. The difference is subtle, but we do recommend adjusting the size in Camera Raw if you plan to resize the image later. In most cases, that means increasing the size of the image in the conversion.

The Resolution setting will not affect the actual output size of the image—only the default output resolution setting for the file. This can simplify your workflow if you need to prepare images for print. For example, you can set this to the resolution you use for printing your images, and the file will be set to that output resolution.

Lens settings

When you select the Advanced option in the Camera Raw dialog, the Lens tab is added to the available controls that include options for correcting chromatic aberration and vignetting.

We discussed chromatic aberration, describing it as color fringing around high-contrast objects. There’s another type of chromatic aberration where the size of the image for each color channel is slightly different. This doesn’t produce color problems in the center of the frame, but it does create color fringing away from the center of the image. This second type of chromatic aberration is the only type Camera Raw allows you to control.

The controls for adjusting this chromatic aberration are split into an R/C slider that controls fringing between red and cyan, and a B/Y slider that controls fringing between blue and yellow. These controls will not affect the center of the image, but will affect the area outside the center, with the maximum effect in the corners.

The vignette controls allow you to compensate for images that have outer edges—particularly the corners—that are darker than the rest of the image. The Vignetting Amount setting determines how much lightening or darkening is applied to the edge of the image, and the Vignetting Midpoint slider determines how large an area will get adjusted.

Calibrate settings

The Calibrate tab is also only visible when the Advanced option is selected. This section provides a variety of controls designed to compensate for inaccurate camera profiles. Camera Raw includes profiles for supported cameras, which describe the color behavior of the cameras. If you feel the profile is inaccurate because it consistently shifts the color in your images toward particular hues, you can fine-tune these controls to compensate. They include controls for the Shadow Tint, which controls the color temperature in shadow areas, as well as hue and saturation adjustments for each of the color channels. These controls are only recommended for advanced users who are very familiar with camera profiles.

Convert

Once you have set all of the options for the RAW conversion, you can click the OK button. The image will be processed and converted based on the settings you applied, and the image will be opened in Photoshop, ready for you to save and optimize. The original RAW capture, however, is left untouched.

Excerpted from “Real World Digital Photography, 2nd Edition;” copyright © 2004 by Katrin Eismann, Sean Duggan, and Tim Grey. Published by Peachpit Press. Used with the permission of Pearson Education and Peachpit Press. To buy this book, visit www.peachpit.com.