Bruce Barnbaum - The Art of Photography - An Approach to Personal Expression

RAW converter programs go by any number of names, many of which do not include the word RAW. Among camera manufacturers, Nikon publishes NX2; Canon publishes Digital Photo Professional; Sony publishes Image Data Converter; and Olympus publishes Olympus Master 2 . In addition, there are standalone conversion programs including Adobe Camera Raw (ACR); Bibble 5 Pro, published by Bibble Labs; Capture One Pro, published by Phase One A/S; DxO Optics Pro, published by DxO Labs; LightZone, published by Light Crafts; and RAW Therapee, published by RT Team as shareware, to name but a few. Because the structure of the RAW file differs from one camera manufacturer to the next, indeed, sometimes from one camera model to the next, and because some manufacturers encrypt their RAW files, make sure the RAW converter you choose is compatible with your camera.

Predictably, each RAW converter program has its characteristics and each program has its preferred sequence of actions referred to as a workflow. Also, as digital technology evolves, software engineers include an ever-increasing number of features in their converter software. Most software publishers offer a trial version, so you can try a few before buying. As with photographic films, enlarging papers, and developers, every RAW converter has its ardent supporters as well as its detractors. Again, as with traditional photography, you’ll be best served by mastering the features of a limited body of software. For the discussion that follows, I’ll use the ACR converter common to both Lightroom and Photoshop. The user interfaces and controls of other converters will be different but the fundamental principals will apply.

In summary, all RAW captures require subsequent processing outside the camera in a RAW converter. Each RAW converter has its unique user interface, controls, features, and workflow, and each will render the RAW file differently, in much the same way that different film developers will produce negatives with different characteristic curves.

While the controls for each RAW converter vary, most allow you to zoom to the pixel level, preview the results of prospective changes as you readjust the settings, and permit you to make iterative adjustments. That is, you can go back and change earlier settings based on the results of subsequent settings, and you can make any number of revisions before clicking on the Open Image button. For the preservation of the RAW capture, be sure the processed file will be saved separately from the original—you want the original RAW file to remain unaffected and the converted file to be saved in TIFF or PSD format.

Figure 11-10. Image converted using Daylight white balance setting

We will look at a brief summary of each of the following operations that are available in a RAW converter:

Demosaicing

White Balance and Camera Profiles

Adjusting the Black Point, White Point, and Contrast

Correcting Aberrations

Sharpening the Capture

Converting the Image to Black-and-White

Output Formats and Bit Depth

Batch Processing

Demosaicing

Demosaicing the color array is the process of filling in the incomplete color information resulting from the brightness data gathered through the CFA (color filter array). That is, the demosaicing process supplies, for each pixel, the two channels of color information not recorded through the specific photosite’s color filter. The RAW converter does so by interpolating from information recorded at neighboring photosites. Because demosaicing requires the estimation of missing color information, and each converter uses a different algorithm, the color rendering of a RAW file will vary from one converter to the next. In other words, the computer fills in the red and green components for each site with a blue filter (and the corresponding channels for the other photosites) based on data from nearby photosites. The demosaicing process results in three grayscale images, one for each of the red, green, and blue color channels, which are integrated by the software into a full color photograph.

White Balance and Camera Profiles

Where the white balance of color film is set by the film’s emulsion and the use of color correction filters (Chapter 6 and Chapter 7), the RAW file is not color balanced. Instead, the camera’s white balance setting is saved as a part of the metadata that accompanies the RAW capture and becomes the default white balance setting in the RAW converter. Importantly, as with the other setting in Adobe Camera Raw, no color correction will be made until the end of the conversion process, so you are free to change white balance settings, select intermediate color temperatures, preview the results, and change again, all without incurring any losses. This gives you immense control at any time, allowing you to change things as your seeing and thinking evolve.

In ACR, the color balance settings are controlled by the Color Temperature and Tint sliders found on the Basic tab. Figure 11-10 shows a RAW capture rendered in ACR using the As Shot color temperature. That is, ACR defaults to the camera’s color temperature setting recorded in the metadata accompanying the capture, in this case the daylight setting of 5500°. If you measured the color temperature when you made the capture (a process discussed below), the measured value will become the default setting in ACR.

The ACR’s White Balance drop down menu offers a number of preset color temperatures including Daylight, Cloudy, Shade, and Tungsten, and you can select any value you wish by moving the Temperature and Tint sliders or by directly entering numeric values. Try the presets, move the sliders, and use the settings that render the image as you wish. As with the other settings in ACR, trying different white balance settings does alter the RAW data and is applied to the processed TIFF or Photoshop format file only when you open or save the image. When you save the converted image the file will be saved as a new file. The RAW file retains all of the information from the capture should you want to go back to your original and try other converter settings.

For images that require precise color fidelity (suppose you’re photographing a 17th century painting for preservation purposes), you can first photograph a neutral gray or white target in the prevailing light. If you are using a DSLR or one of the more advanced point-and-shoot cameras, the camera will include the measured color temperature in the metadata, and the field determined color temperature will become the default white balance setting in the RAW converter.

Color temperature and balance are but two elements of the larger subject of color management—the science and art of causing each color in the scene to be rendered identically throughout the digital process. It is the goal of a color management system to cause the colors in front of the camera to be accurately rendered on your computer display, on the Internet, and on the final print. In reality, the goal cannot be achieved fully because each physical device has a limited universe of colors that it can capture, display, or print. Furthermore, reflective images (prints) have different properties than do light-transmitted images (such as computer displays and transparencies). The universe of color that any device can record or reproduce is known as its “gamut” and, in the real world, the gamut of the camera is larger than the gamut of the computer display, and the gamut of the display is different from and often larger than the gamut of an inkjet printer. Figure 11-12 shows a graphic depiction of the gamuts of the visible spectrum,, the Adobe RGB color space, the smaller sRGB color space, and the gamut for a typical inkjet printer.