Originally a Photoshop file format plug-in, Adobe Camera Raw (ACR) has evolved into an essential tool for processing digital camera Raw image files. Raw processing is versatile and necessary for image quality control, workflow ease, and efficiency. It provides a powerful method for working with all aspects of digital capture. In fact, new versions of ACR can be used to reprocess legacy Raw files. A Raw file is the digital equivalent of a film latent image that hasn’t been developed. As the software improves, the processing can improve. There is no analogue to this amazing technology in traditional (film-based/wet darkroom) photography. Check the Adobe website for ACR updates regularly.
Digital camera sensors use massive rows and columns of photodiodes (called an “open field array”) to capture linear grayscale data. A red, green, or blue filter caps each photodiode (conventional digital sensors have twice as many green photodiodes as red and blue to mimic the increased sensitivity to green light of human vision). At the moment of exposure photonic energy is recorded by the sensor’s photodiodes and the measured grayscale data is tagged as Red, Green, or Blue respectively. It is processed in-camera to produce the pixels that form an image file. In fact, there is a considerable amount of processing performed by in-camera software (you have some control over processing through the camera menus). Two important examples are:
- All digital captures are initially Raw but may be converted to other file formats (the usual choices are Tiff or Jpeg) either by default (some point-and-shoot digital cameras only save Jpeg image files) or because the camera menus are configured to do so. Be sure to configure your camera for Raw capture.
- The pixel data is mapped to a color space (ProPhoto, Adobe RGB or Adobe RGB (1998), and sRGB, are common choices). Imagine a digital color space as a set of crayons. ProPhoto is the big box and sRGB is the small box. The two Adobe RGB color spaces are smaller than ProPhoto but much larger that sRGB and they match well to the color space of most inkjet printers. Color spaces include a gamma setting. Gamma is designed to render the linear data to a non-linear representation more like human vision. If provided, use ProPhoto; if not, Adobe RGB/Adobe RGB (1998).
The image on the back of a digital camera is a Jpeg file; it is not an accurate representation of the Raw capture or color data that exists in the Raw image file. Useful for checking composition and focus, this Jpeg is a poor indicator of color balance or exposure. The histogram, if available, is better for judging exposure; color balance can be controlled by profiling the camera and/or by adjusting it in ACR.
PROCESSING IMAGE FILES IN ACR
ACR and Photoshop use very different technologies to process image files. ACR uses parametric control (as does Lightroom); the data created in-camera (stored in the pixels of the image file) is not altered in ACR. Instead, all the editing performed on the image file is recorded as a set of instructions (metadata) that travels with the file (for example, when it is opened in Photoshop). This makes it possible to reprocess Raw image files, at any time, and rework legacy Raw files with newer versions of ACR (or any other Raw processing application).
Photoshop rasterizes pixel data. When a Raw image file is opened in Photoshop the ARC parametric instructions are read and the edits encoded before the file opens. These instructions, and any additional edits performed in Photoshop, are made permanent when the file is saved.
It’s a good idea to use the full screen mode when working in ACR. Full screen presents a larger dialog box and image view area. It also hides the desktop and any other applications that may be open. The Film Strip, along the left edge, displays images selected from Adobe Bridge. The first step when using ACR is to select the image(s) in the Film Strip for processing. Single files are selected by clicking on them; the image will load in the preview area. All the images In the Film Strip can be processed as a group by clicking on the Select All button (only the top image in the Film Strip will preview). You can select a single image, process it, and apply the editing to others in the Film Strip by using the Synchronize button.
The magnification of the selected image can be changed with the magnification control (bottom left of the image title). Magnification can also be changed by pressing the Command and minus/plus key. A Tool Bar is above the image area and the Workflow Options link is below.Positioned top right are a live histogram of the displayed image (it updates as edits are made), a live RGB image information pallet (move the cursor over the image and the RGB numbers will display), and image metadata (the aperture, shutter speed, ISO, and lens focal length used when the image file was created).
Below are tabs for the ACR image adjustment panels. Basic is the default panel and includes options for editing image color and tonal values. Edits made in the image adjustment panels are global; they are applied to the entire image file, and to all the images selected in the Film Strip. The Tool Bar provides a small set of local editing options.
Before processing an image there are two ACR configurations that should be performed. First, click on the Workflow Options link below the image area. An important panel, it is used to determine:
- Depth– select 16 Bits/Channel to conserve the pixel data in the Raw file.
- Size– the native resolution of the image file should be the default setting (it does not show a “+” or “-“ symbol).
- Resolution– 240 ppi is the default. The pixel per inch of the image file is easily modified here or in Photoshop prior to printing.
There is also an option for opening the file in Photoshop as a Smart Object. Second, select the Camera Calibration tab to access the Camera Profile panel and click on the Name popup menu. With the exception of the Adobe Standard profile, all others are Camera Matching profiles specific to the camera used to produce the image file selected from the Film Strip (ACR 3.1 and ARC 4.4 are legacy Camera Matching profiles).
Select different profiles and observe the impact on the image; changes can be negligible or relatively dramatic. Use the profile that provides the best starting point for image editing (there are no “right” or “wrong” choices). The default profile, ARC 4.4, can be changed to any profile listed by clicking on the flyout popup menu (to the right of Camera Calibration) and selecting Save New Camera Raw Defaults. If you author custom profiles for camera(s) load them into your computer system for access in this panel:
Mac OS- Library/Application Support/Adobe/CameraRaw/CameraProfiles
Windows Vista- C:UsersAllUsersAppDataLocalAdobeCameraRawCameraProfiles
Windows XP- C:Documents and SettingsAll UsersApplicationDataAdobeCameraRawCameraProfiles
You may want to click on Auto adjustment to view how ACR would process the file; click on Default to restore the image file to its original state.
- White Balance- There are two primary controls for adjusting color balance in the Basic image adjustment panel, White Balance and Temperature/Tint (these work particularly well in concert with the White Balance Tool located in the Tool Bar). There are additional color balance options in the H/S/L Grayscale and Split Tone image adjustment panels. To alter the color balance of a Raw image file in ACR try (in no special order):
- The Auto function.
- Use one of the presets available in the White Balance popup menu.
- Use the White Balance Tool (eye dropper) to autocorrect on a textured white or neutral gray area in the image.
- Use the hue, saturation, and luminance controls in the H/S/L Grayscale tab panel.
- Use the Auto function, one of the White Balance presets, or the White Balance Tool; then tweak color using the Temperature/Tint sliders and/or the options available in the HSL/Grayscale tab panel.
- Use the Auto function, a White Balance preset, the White Balance Tool, and H/S/L; then tweak color using the Split Tone tab panel (more about this below).
- Exposure– Digital exposure follows the same formula, E = T x I (Exposure is the product of Time multiplied by Intensity), as all other photographic systems. Time is controlled by the shutter speed, Intensity by the aperture. Every scene has an optimal exposure (E) based on the subject, the photographer’s intention, and the ISO of the film or sensor. In traditional photography Exposure (followed by development) is usually based on producing a minimum film density to achieve the desired tonality in the print (the core concept behind the Zone System).
- This is not the optimal approach for digital capture. The primarily goal when capturing light with a digital sensor is to increase exposure, as much as possible (to maximize the amount of data recorded), before losing detail in higher tonal values. The idea is to generate as much data through the sensor as possible but avoid clipping (“blowing out”) the RGB channels. Too little exposure in a digital capture, including Raw, will compromise dark tonal values and add noise to the shadow tonalities. Noise has a tendency, varying by camera, to increase as the ISO increases.
- You must manage the ever-present compromise between data captured in high values and noise in shadows. Low contrast scenes/subjects are relatively easy to manage; high contrast scenes/subjects require careful exposure and processing for optimal results. This is one reason why reading a histogram (on the camera’s preview screen and in ACR) is important.
- Use Exposure to adjust the overall density of the image. When processing an image file with higher than normal contrast you may find that slightly adjusting highlight density downward can improve clipping of the high values; the editing options in the Curves image adjustment panel provide more precision than the Exposure slider. Watch how the histogram changes using Exposure or Curves.
- Recovery– ACR Recovery can preserve high tonality data if it exists in just one of the RGB channels (even if data is missing in another channels). This is a powerful method for reducing clipping and managing high contrast image files. If all three channels (red, green and blue) are clipped in the original exposure, however, Recovery cannot generate detail where it does not exist. Increasing it will only lower the contrast of the image file. The best image quality comes from having some detail in all the channels and this is determined by the original exposure. Hint: Click the Shadows or Highlights option (upper left and right corner of the histogram) or hold down the Option key when using either Exposure or Recovery to preview the effect of the edit on the image file’s brightest values. Clipped Shadows will display in blue; Highlights in red.
- Fill Light– Increasing Fill Light opens (makes less dense) the darkest tonal values in an image file. It is a preferred method for opening up shadow values before processing in Photoshop. Be sure to view this edit at 100% image magnification (or more) to determine if increasing Fill Light reveals noise.
- Blacks– 5 is the default Black setting. Small changes to Blacks can be dramatic. Hint: Hold down the Option key to preview image areas that are black. As black is added, with the Option key pressed, the image areas will increase in size.
- Brightness– Brightness acts as a middle tone adjustment, working to lightening or darken the image overall. It is best used after Exposure is adjusted.
- Contrast– Contrast is a simplified, and not as precise, version of Curves. Use sparingly, particularly if you’ve already increased the Blacks setting for an image.
- Clarity– A middle tone enhancement tool, Clarity is a powerful ARC option that can simplify processing in Photoshop. It increases the local contrast (sometimes referred to as “micro contrast”) in middle tone values without destroying date in the black and white tonalities of an image. Increasingly middle tone contrast tends to improve the illusion of sharpness.
- Vibrance– Vibrance is a non-linear saturation tool that is subtle compared to the Saturation option. It is useful for improving color saturation in skin tones, for example. Compared to Saturation it is far less destructive to image file data.
- Saturation– This control is not subtle. Used liberally it can result in a loss of detail, particularly in the high tonal values. Watch the Histogram for clipping.
- Sharpening– Sharpening is a three-stage process for inkjet printing: Capture sharpening (designed to recover optical sharpness in the image file), Creative sharpening (done to preference), and Outputsharpening (designed to balance dot gain; the slight ink spread that occurs when a droplet of ink is applied to the printing surface). The Sharpening options in the Detail panel are designed for Capture sharpening. A default Amount setting of 25 is automatically applied to all image files processed in ACR. Amount is a percentage, not an absolute (it will vary by camera):
- Amount– Increasing Amount progressively enhances contrast between dark and light edges. Done aggressively it will produce a noticeable halo.
- Radius– softens the Amount halo by blending it into nearby image areas.
- Detail– with Amount and Radius thoughtfully balanced (judged at 100% magnification or greater), Detail functions as a “textural” control. Increasing Detail will emphasis texture. It is relatively powerful and should be used judiciously.
- Masking– has an unusual ability to soften texture, but does a good job of respecting defined edges.
- •Hint: The default Amount of 25 can be turned off in the Camera Raw Preferences panel. Select Preview images only from the Apply sharpening to popup menu.
- Noise Reduction– Noise is random, non-imaging forming data generated as a by-product of the imaging system. It is the digital photography equivalent of noise in an audio system, phone connection, or television signal. Noise is minimized when image files are created at a digital camera’s base ISO setting (some noise is always present). More noise accumulates as higher ISO settings are used.
- How well digital cameras control noise varies considerably. Some cameras produce much less noise, at a given ISO, than others. Some provide on-board noise reduction through the camera menus (be aware that camera noise reduction typically slows down file processing speed).
- ACR Noise Reduction is used primarily to reduce shadow area noise in image files made at higher than normal ISO settings. In general, ACR NR can reduce noise equivalent to one ISO stop (it can make an ISO 800 image file look more like ISO 400). Because ACR NR is Parametric, it is best to performance as much noise reduction in ACR as possible, before processing in Photoshop.
- Judge the effect of ACR NR at maximum image magnification (400%). Increasing Luminance Noise Reduction will eventually decrease image detail. Landscapes often have an abundance of high frequency detail; portraits, on the other hand, usually have low frequency detail. Adjust Luminance and Color noise reduction appropriately. Remember, adjusts made in this panel affect the entire image.
- Chromatic Aberration– is most noticeable as color fringing on edges (particular dark against light areas in an image). Check for fringe colors at maximum magnification (400%). Use the Defringe drop-down menu to restrict the action of the Fix sliders to highlights, or to allow the effect over the entire image.
- Lens Vignetting– is the tendency for some lenses (particularly zoom lens) to produce less exposure along the outer edges and corners of an image. Amount darkens or lightening these areas. Midpoint expands or contracts the effect.
- Post Crop Vignetting– because vignetting can be used for creative effect, Post Crop can apply a vignette to images after they are cropped in ACR.
- Heal– The Heal brush is designed to mimic one area and apply a correction to another by matching texture and detail.
- Clone– The Clone brush duplicates the sampled area to the selected area. It is literal by comparison.
The Point Curve will be familiar to Photoshop users. The default setting is Medium Contrast; there are four edit points applied to the curve that can be clicked and moved (the Input and Output code values appear below). The Parametric Curve provides a set of editing controls: Highlights, Lights, Darks, and Shadows. Manipulating these sliders is equivalent to moving edit points on the Point Tone Curve. The three triangle controls at the bottom of the Parametric Curve are used to refine the edits made with the sliders.
Hint #1: When using the Point sub-panel hold down the Command key, move the cursor across the image, and a moving point on the Curve will indicate there tonal values fall.
Hint #2: To retain detail in high tonal values try adjusting the Hightlights slider in the Parametric Curve. This option, used with Recovery in the Basic image adjustment panel, can sometimes perform small miracles.
HSL/Grayscale– This image adjustment panel is both convenient and powerful. Click on the Convert to Grayscale button to process an RGB image file to black and white using eight Hue, Saturation, and Luminance values (Reds, Oranges, Yellows, Greens, Aquas, Blues, Purples, and Magentas).
The default Convert to Grayscale setting tries to maintain the image contrast of the original color image. It provides grayscale conversion combining the control of a Photoshop Black/White Adjustment layer and a Hue/Saturation layer.
Use ACR HSL to balance, tweak, or manipulate colors in an image file. It provides excellent control for color editing, and is a good reason to program Work Flow Options to open image files as Smart Objects in Photoshop (allowing you to move a Raw image file from Photoshop back to ACR).
Split Toning– The Split Toning panel is most often used to modify images converted and processed to grayscale in the HSL/Grayscale panel. Many photographers do not realize that Split Toning can also be used to tweak color balance for RGB images (images not converted to grayscale). For RGB images first increase Saturation, then adjust Hue to finesse highlights and shadow color (effective for cleaning up color tints for snow, water, or a skin tone).
Lens Correction- This ACR panel is designed to correct (or, at least, improve) predictable issues related to the optical system of digital cameras:
Camera Calibration– As mentioned earlier, camera profiles are applied through this image adjustment panel and should be selected prior to processing image files. The sub-panels: Shadows, Red Primary, Green Primary, and Blue Primary can be used to modify the effect of a selected camera profile.
Presets– Any ACR processing configuration can be saved and applied to future image files through the flyout panel (in the title bar right of Presents). Open the panel and select Save Settings. Likewise, if you want ACR to start up preconfigured to your settings select Save New Camera Raw Defaults.
Presets can be a tremendous time saver by semi-automating repetitive image file editing.
ACR Tool Bar (left to right):
- Zoom Tool (press Z)- Used to increase image magnification. Its an easy way to magnify a specific image area.
- Hand Tool (press H)- If the image magnification exceeds the viewing area use the Hand Tool to click and drag the image.
- White Balance Tool (press I)- A powerful tool for adjusting white balance. Use by clicking on a detailed white or gray value in the image area. Hint: You can access the White Balance Tool while the Zoom, Hand, Color Sampler, Spot Removal, Red Eye Removal or Adjustment Brush is active by holding down the Shift key.
- Color Sampler Tool (press S)- As mentioned above, the RGB data located under the histogram is live; move the cursor over an image and the values will automatically update. Use the Color Sampler Tool to place up to nine “sticky” measurement points. These data will be displayed under the Tool Bar above the image. Cancel single measurement point by Option-clicking; clear all by clicking the Clear Samplers button.
- Crop Tool (press C)- The Crop Tool provides options for cropping an image through its popup menu (click on the small arrow in the bottom right corner of the icon). Select the Clear Crop option to cancel.
- Straighten Tool (press A)- The Straighten Tool works with the Crop Tool. Click and drag to establish the desired vertical or horizontal line. The Crop Tool will become immediately active. Press Return to apply the edit or click on the Crop Tool to further refine or cancel it.
- Spot Removal (press B)– There are two ACR methods for local repair and retouching on image files available through the Type popup menu, Heal and Clone. They perform similarly to the retouching options in Photoshop but function differently (and more like those found in Lightroom):
- Red Eye Removal (press E)- This tool has two settings, Pupil Size and Darken. Click and drag the cursor over a red eye (ACR will attempt to automatically size the active selection based on content) and adjust if necessary by dragging the edges of the selection or use the Pupil Size slider. Use the Darken slider to desaturate the selected area.
- Adjustment Brush (press K)- This panel provides an extensive tool set for local, rather than global, image editing. Size, Feather, Flow, and Density of the brush are controlled in the bottom sub-panel (the Size will be indicated by a solid circle; the Feather by the outer circle). The top panel programs the brush effect. These effects can be adjusted before or after the brush is used to make the edit.
- Graduated Filter (press G)- The Graduated Filter, using options identical to the Adjustment Brush, allows editing across larger contiguous image areas. Hint: For a quick and effective introduction to the Adjustment Brush and Graduated Filter tools visit www.adobe.com/go/lrvid4008_ps.
For more information download free Help PDF’s on Adobe Creative Suite 3, 4, and 5 (including extensive descriptions of Camera Raw) at: