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Digital Imaging Basics, Workflow, and Calibration Every journey begins with the first step. Unfortunately, for many, the temptation to skip the first step is enhanced by the belief that they already know how to take pictures. we were kids, haven’t we? Modern cameras do everything automatically, don’t they? For consistent success, you need to predict the outcome of the image capture with 1 592120c01.indd 1 certainty—and for professional results, you can’t rely on the display on the back of the camera.
Chips and Pixels All cameras function like human eyes (Figure 1.1). In both, a lens focuses light through a small hole (iris) onto a receptive surface (retina/film/chip) that translates the varying intensities and colors of the light into meaningful information. The main distinguishing feature between different cameras and the eye has to do with the receptive surface.
blue for each pixel. We, therefore, think of these pixels as being in three “channels” (Red, Green, and Blue) simultaneously so that the complete image is recorded as three different black and white (B+W) images that form the full-color version. This concept will be important when we get to color correction. The number and density of receptor sites on the chip determine the resolution of detail.
The dynamic range of a captured scene is an important yardstick for quality (Figure 1.2). This is the brightness range from dark to light that affects how much detail can be rendered in the darkest and lightest portions of the scene. Dynamic range is often represented in f-stops. Digital cameras can often capture a range of 11 f-stops from black to white, whereas a paper print from a desktop inkjet printer might have, at best, a range of five f-stops.
JPEG is a file format that was developed to reduce file size by using mathematical algorithms that simplify the pixel structure in the bitmap image. This process is considered lossy because some image detail is “lost” during the process. Digital cameras apply a conservative level of compression or size reduction, and this is generally considered visually lossless. This does not mean that there is no loss—just that the loss is not apparent at first glance.
If you are concerned with the best possible quality, then you probably will prefer to record the camera’s RAW signal and process this data using your computer software in a RAW file workflow. Doing so complicates the process slightly by adding an additional post-processing step to your photography workflow.
I highly recommend that you choose a simple, gray desktop color and select a gray interface option for the overall color scheme for your computer. The idea is to eliminate as many color distractions as possible for the environment in which you will be making color decisions. If the background behind your images is bright blue, you will tend to see everything as warmer than it is because of the color contrast with the blue background.
3. Verify the integrity of the backup. (This automatically verifies the first copy.) 4. Once you are satisfied that the files are OK, you can reformat the card in the camera before shooting more images. Of course, you might not have enough time to copy, duplicate, and verify while you are shooting, so you might need to have multiple cards on hand. Always strive to have two copies of every image file at any one time.
organization I have on my hard drives. To accomplish this, you need to begin with some organizational structure. This is how I set up my hard drives (Figure 1.5). Figure 1.5 Dual external hard drives set up as Archive and Archive_Backup 592120c01.indd 9 9 ■ B a s i c D i g i ta l C a p t u r e Wo r k f l ow I keep all my images on an external hard drive—this is my image archive that I duplicate onto a second hard drive.
chapter 1: D i g i ta l I m ag i n g B a s i c s , Wo r k f l ow, a n d C a l i b r at i o n ■ 10 592120c01.indd 10 Figure 1.6 The Lightroom Library module shows the hard drive folder structure at the left in the “Folders” pane. Lightroom has become my software tool of choice for organizing and processing my growing image collection. Just about every imaging task—short of retouching— can be accomplished with it. Its functions include making slideshows, printing, and making web galleries.
To calibrate your camera, you must shoot a test. The test shot will need to include some kind of standard target (Figure 1.7). 11 The most widely used target is the X-Rite ColorChecker 24 Patch Classic. Originally known as a Munsell chart, this target has been in widespread use for at least 50 years in the motion picture and television industries. You should be able to purchase one at any camera store.
The testing procedure involves a series of steps, which are summarized here: 1. Establish lighting that mimics the conditions for 6500º K and 2850º K—open shade and tungsten lights indoors. 2. Shoot a range of exposures to determine your camera E.I. (exposure index, ISO, or ASA rating). 3. Import RAW files into Lightroom or ACR, and white balance to the light-gray patch. 4. View the series of exposures in Lightroom or ACR and apply “Zero slider” settings. 5.
Fluorescent Lighting Shooting a test under fluorescent lighting is almost not worth the effort, because each uncontrolled situation you encounter will be different. Also, fluorescent lighting is a really unbalanced spectrum with big gaps and spikes in the frequencies represented. These situations almost always require some selective color correction in Photoshop after processing, so the kind of calibration you achieve here will be of limited use.
chapter 1: D i g i ta l i m ag i n g B a s i c s , Wo r k f l oW, a n D c a l i B r at i o n ■ 14 Figure 1.9 Spot meter readings are taken from the camera position. The Mysterious “K” Factor The mid-gray patch is calibrated to 18 percent reflectivity; this is supposed to match the 50 percent luminosity that light meters are calibrated to—but, in fact, it is off by roughly 1/3 to ½ stop. Why this is so is unclear. Many reference “gray cards” are referred to as 18 percent gray.
A spot meter can read directly from the mid-gray patch (third from the right on the bottom of the ColorChecker); open up 1⁄3 stop to get the base exposure. If you don’t have a spot meter, use an incident meter and take a reading from the subject position, pointing the white dome at the main light source (Figure 1.10). The ideal way to take exposure readings, at least for the test, is to use a hand-held light meter. A hand-held meter is better than relying on the camera meter for a number of reasons.
are not accurate except as a rough approximation of the camera JPEG. We are looking for better than JPEG performance; otherwise, it’s not worth shooting RAW. In practice, I find that relying on the LCD almost always causes you to underexpose the shot. Of course, with a lot of experience, you can learn how overbright the image on the LCD needs to be to arrive at the correct exposure. I personally prefer a more controlled approach. Figure 1.
Importing Shots and Evaluating Exposure Now, you have to evaluate the shots to determine the best exposure. I will first look at how this is accomplished in Lightroom. Import the image files into Lightroom (Figure 1.13). Use the General – Zeroed develop preset to get everything set up with no adjustments. Make sure you are using the “Camera Neutral” calibration preset to get as unbiased a rendering as possible (Figure 1.14).
chapter 1: D i g i ta l I m ag i n g B a s i c s , Wo r k f l ow, a n d C a l i b r at i o n ■ 18 592120c01.indd 18 Figure 1.15 Evaluate the exposures for the best overall exposure and zoom into the most likely candidates. Look for the exposure that gives you a reading close to 51 percent and, very importantly, without having the white patch go over 90 percent. Move the cursor into the image and look at the numbers that show up right under the histogram display, as shown in Figure 1.16.
19 ■ B a s i c D i g i ta l C a p t u r e Wo r k f l ow Figure 1.16 This exposure has a good mid-gray patch reading, but the white patch is clipped. Figure 1.17 The mid-gray patch is still close, but the white patch goes past 90 percent. 592120c01.
Figure 1.18 The mid-gray patch is somewhat low, but the white patch is now in a safe range at 85 percent. chapter 1: D i g i ta l I m ag i n g B a s i c s , Wo r k f l ow, a n d C a l i b r at i o n ■ 20 Figure 1.19 Highlight detail can be recovered with the Recovery slider. 592120c01.
The shooting procedure for ACR is the same. Once you have shot the exposure sequence, open the RAW captures in ACR, either from Photoshop or Bridge. Make sure you have all your slider settings at “zero” and your tone curve set to “linear,” and then do a white balance and synchronize all the captures before you start looking for the best exposure. ACR does not display the same Linear ProPhoto feedback numbers that Lightroom uses. (The engines are identical, but the RGB numbers are not.
Building a Camera Calibration RAW processing software is designed to interpolate color information from varying brightness of pixel sites that have a colored filter of red, green, or blue. In essence, there is no color in the RAW data—color is inferred by measuring the brightness of pixel clusters. The colored filters covering the tiny pixel sites are not perfect and, manufacturing processes being what they are, there is some variation from camera to camera even from the same manufacturer.
23 ■ B a s i c D i g i ta l C a p t u r e Wo r k f l ow Figure 1.22 The DNG Profile Editor opens with the Color Tables tab active. Figure 1.23 Open a test shot and click on the Chart tab. Follow the instructions and position the four colored circles (dots) over their respective patches on the target. You can zoom in on the chart image to make it easier to position the dots in the middle of the patches (Figure 1.24). 592120c01.
Figure 1.24 You may need to zoom in to position the colored dots accurately. Select 6500 K only from the drop-down to identify the color temperature of the table you will create. Click the Create Color Table button, and you will be brought back to the Color Tables tab with all the patch colors mapped onto the Color Wheel. The table is created (Figure 1.25). If the test was shot correctly and you chose the appropriate exposure, there will be no problems.
Next, you will create the table for 2850º K. Open the tungsten test shot. This is more likely to be at 3000º K to 3400º K, depending on the lights you actually used, but it will be close enough for this purpose. Once the tungsten test shot is open, click the Chart tab, select 2850 K only as the table to build, and position the dots (Figure 1.26). Again, click the Create Color Table button and you’ll be back at the Color Tables tab, this time with the 2850 table created (Figure 1.27).
At this point, all you need to do is select: File > Export your camera name profile and give the file a meaningful name (Figure 1.28). The DNG Profile Editor finds the correct location for the profiles so that they can be used in ACR or Lightroom. Figure 1.28 Save the complete camera profile from the File menu. chapter 1: D i g i ta l I m ag i n g B a s i c s , Wo r k f l ow, a n d C a l i b r at i o n ■ 26 592120c01.
creation of DNG camera profiles within Lightroom. There are very good instructions with the software, but it almost doesn’t need any because it is very easy to use. Launch the ColorChecker Passport application and you will see a wizard interface with instructions that walk you through the process (Figure 1.30). 27 ■ B a s i c D i g i ta l C a p t u r e Wo r k f l ow Figure 1.29 The X-Rite ColorChecker Passport target Figure 1.30 The ColorChecker Passport software provides on-screen instructions.
Drag two different test shots (preferably under shade and tungsten light) into the image window. The software will automatically locate the patches for each shot. Then simply click the Create Profile button, name the resulting file, and you’re done. (Figure 1.31) Figure 1.31 Once you drag the test images in, you can create and save a camera profile. chapter 1: D i g i ta l I m ag i n g B a s i c s , Wo r k f l ow, a n d C a l i b r at i o n ■ 28 Figure 1.
29 The Lightroom plug-in is particularly easy to use, because you never have to leave Lightroom. The plug-in is invoked from the Export dialog; select X-Rite Presets from the Export To drop-down menu (Figure 1.32). The dialog changes specifically to accommodate saving DNG Profiles (Figure 1.33). The resulting file is automatically saved to the correct location. Both Calibration systems work well to provide customized camera profiles for your specific camera.
3. After applying the camera profile, go to the Basic pane, set your white balance to As Shot using the WB list box, and then select Set Default Settings from the Develop menu (Figure 1.35). You’ll receive a warning and a confirmation of the camera model and serial number. 4. Click the Update to Current Settings button. Now every time you import a RAW file from this camera, it will appear with these settings and camera profile. Figure 1.34 Apply a camera profile in Lightroom.
In Adobe Camera Raw Similarly in ACR, to apply the profile, follow these steps: 1. Open the images in ACR. 2. Select them, click on the Camera Calibration tab, and select the profile you saved earlier from the Camera Profile pop-up (Figure 1.36). 31 3. To save a new Camera Raw Default, apply the profile and then go to the Basic pane. 4. Set the white balance to As Shot, and set any additional adjustments you prefer. 5. Select Save New Camera Raw Default from the settings drop-down (Figure 1.37).
Editing Camera Profiles for Better Skin Color One common issue with digital capture is that any red component in the skin color can be overemphasized, and people often complain that the skin color turns out too red! If you find this to be the case with your files—even after you’ve built a calibration—you can tweak the red out in the DNG Profile Editor. First, you must arrange to shoot a test with a subject that exhibits the red skin defect in your digital captures.
Figure 1.39 Edit color using the Hue and Saturation sliders. Exposing to the Right You might have heard that it’s a good idea to “expose to the right of the histogram.” Experts often recommend doing so when you evaluate the exposure based on the histogram display on the LCD on the back of the camera (see the accompanying graphic).
Working with Your Calibration Although a full exploration of Adobe Camera Raw or Lightroom is beyond the scope of this book, I can offer the following general breakdown for RAW file processing using Adobe products. Ideally, you should shoot a gray card in the same lighting as the bulk of your subject matter. Have the subject hold the ColorChecker or a gray card. (For the test shown in Figure 1.40, I stood in for the subject and had an assistant shoot for the gray card.
35 Similarly, in ACR click the Synchronize button (located in the upper-left corner) and click OK in the resulting dialog, as shown in Figure 1.46. If you’ve done a good calibration and you’ve exposed properly, you seldom have to do more than slight brightness and contrast adjustments to “cook” the image to taste! ■ B a s i c D i g i ta l C a p t u r e Wo r k f l ow Figure 1.41 Sync the files in Lightroom. Figure 1.42 Synchronize the files in ACR. 592120c01.
If you do not have the opportunity to shoot a gray card, you can select a default from the White Balance drop-down in the Adjust tab (ACR) or the Basic pane (Lightroom) or you can accept the As Shot settings; however, a gray card takes all the guesswork out of the color and can save a lot of post production, especially if you are working with a large volume of images.
• Open the ideal exposures from the shade and tungsten lighting shots in the color calibration software (X-Rite or Adobe), build a camera profile, and then save it. • Set this calibration profile as a camera default in either Lightroom or ACR. Putting Color Management in Context Color management is a relatively new discipline that is still evolving.
chapter 1: D i g i ta l I m ag i n g B a s i c s , Wo r k f l ow, a n d C a l i b r at i o n ■ 38 592120c01.indd 38 numerical representation is currently CIE L*a*b* (CIELAB, essentially the same as Lab in Photoshop). Profiles are generated by capturing the color rendering of specific devices and mapping the results to the numbers required to generate colors on that device.
For our purposes, color management simply involves calibrating the monitor, choosing an appropriate workspace, and utilizing printer profiles at output. You do not absolutely need anything more exotic than Adobe RGB as your workspace. If you shoot RAW, as you should, then there really is no absolute need for a custom camera profile because the RAW data can be processed into a standard workspace in ACR. The calibration steps we’ve just gone through determine how your color is rendered into the workspace.
