Batch Processing
To save time, RAW converters permit the batch processing of selected captures and will run in the background while you edit a different image. This means that you can apply the settings for a particular subject and lighting condition to any number of captures. To batch process in ACR, select the RAW captures you want to batch process using Command-Click (Mac)/Control-Click (PC) in Photoshop Bridge. Press Command-R (Mac)/Control-R (PC) to open ACR, click on one of the images listed on the left-hand side of the window, and fine-tune the selected capture using curves, color balance, or any of the other adjustments. When you are satisfied with the settings, press the Select All button in the upper left-hand corner of the window, then press the Synchronize button immediately below. The Synchronize panel will prompt you for a list of the adjustments you wish to apply to the other captures; the default is to apply all of the settings other than Crop, Spot Removal, and Local Adjustments. Because you selected captures of similar subjects under similar lighting conditions, you can go with the defaults unless you have a specific reason not to apply a particular setting to a capture. Press Save Images located at the bottom left. ACR will present the Save Options panel; complete the panel and click on Save. ACR will apply your settings, convert the captures, name, and save the converted files to the designated file folder.
High Dynamic Range Images—The Extended Zone System for Digital Photography
Suppose the brightness range of a scene exceeds the dynamic range of the sensor. The histogram will touch each edge as shown in Figure 11-16. This is where high dynamic range imaging comes into play.
Figure 11-16. Another histogram where the brightness of the scene exceeds the dynamic range of the camera
While the brightness range of the subject cannot be recorded in a single exposure, the entire range can be recorded, with full detail, in a series of captures that are later integrated into a single image. This is what is known an high dynamic range imaging (HDRI). The procedure is to first make a series of captures at various shutter speeds that, when combined, record the entire brightness range of the scene. You later combine two or more of these captures into a single photograph that has full shadow, midtone, and highlight detail.
Here’s a good way to find a starting point for optimum results. Use a tripod, either a remote/cable release or the camera’s self-timer, and mirror lock-up, if available, to eliminate vibration and to record all of the captures in registration. Focus any way you like (on a stationary subject) and then set the camera to manual focus to assure the camera does not change focus with successive captures. Set your camera to manual exposure mode (you don’t want to change depth of field), select an aperture based on your desired depth of field, and make a test capture. Review the histogram of the test exposure and adjust the shutter speed (but don’t change the aperture or refocus as changes will affect the depth of field or image magnification) so that the highlight (right) side of the histogram falls approximately one-quarter of the way from the right edge of the display. Now make your first exposure of the series.
Increase the exposure by a full stop and expose again. (Note: Generally, full stop bracketed increments are fine, though you may prefer greater or lesser steps.) Review the histogram—it will have moved to the right. Again, increase the exposure by a stop and expose again. Review the histogram again—it will have moved farther to the right. Repeat while incrementally increasing the exposure and reviewing the histogram until the shadow (left) side of the histogram enters into the display and falls approximately one-quarter of the way from the left edge of the histogram. That’s it! You’ve now recorded the entire brightness range of the scene.
Even if you don’t have a tripod, it is worth trying continuous drive and auto bracketing (where the camera automatically captures a series of shots with differing exposures). Hold the camera steady, lock your elbows in, hold your breath, and squeeze off your multiple exposures. Shorter focal length lenses and higher ISO settings will help. Pixels are free, so give it a try.
Now that you have recorded the full dynamic range, you’ll combine the captures to make a final image encompassing the entire brightness range of the scene. You may not need all of the images, as there is will be significant overlap. Perhaps just two will suffice. Maybe three. Possibly more, though unlikely, and in most cases, unnecessary. There are a number of ways to combine several captures into a single image, and combining additional or different exposures will produce a different result, so if you are not satisfied with a particular combination, try different combinations.
Below, I describe four different approaches to merging multiple exposures. For approaches #1 and #2, you should work directly from your RAW files. For approaches #3 and #4, you will need to start with TIFF or PSD files. If you plan to use any of the approaches other than the first two and have not done so, convert your RAW images into TIFF or PSD format using the converter’s default settings. Save the files using names that include appropriate descriptions such as “Forest_Shadows” for the file with good shadow detail, “Forest_Midtones” for the file with the good midtones, and “Forest_Highlights” for the file with the good highlight detail. The techniques discussed below require that all of the images be of the same pixel dimensions, so work with uncropped images.
Now that the files are ready, we will look at four methods in which several captures can be combined. The choices include:
Using the Merge to High Dynamic Range Function in Photoshop
Using Two Captures and a Luminosity Selection in Photoshop
Using Layers in Photoshop
Third Party Software
1. Using the Merge to High Dynamic Range Function In Photoshop
I will first discuss Photoshop CS4 and then discuss HDR Pro found in CS5 at the end of this section. In Photoshop CS4, a high dynamic range (HDR) image is rendered in a two step process. In the first step, two or more exposures are combined into a single 32 bits/channel document using the Merge to HDR function. In the second step, the resulting 32 bits/channel file is downsampled to a 16 bits/channel and saved. The 16 bits/channel file can then be further edited in Photoshop. CS5 introduces a new feature, HDR Pro, that offers additional controls and integrates the combining of information into a 32 bits/channel file and the downsampling to 16 bits/channel into single procedure.
In CS4, you first combine any number of RAW captures into a single 32-bit/channel HDR image, which is so enormous that it provides a nearly open-ended numerical scale having the capacity to represent the dynamic range of any scene. In the second step, you direct Photoshop to convert the 32-bit/channel file into an editable 16-bit/channel file using one of four methods offered by Photoshop.
To accomplish the first step, merge the files; in the File Menu, select Automate and choose Merge to HDR, which will open the Merge to HDR dialogue box. In the Merge to HDR dialogue box, use Browse, select the RAW captures you wish to combine, and, if the captures were handheld, check the Attempt to Automatically Align Source Images box, and then click OK. Photoshop will load the files, perform some processing, and open another Merge to HDR dialogue box. Be sure the bit depth in the dialogue box is set to 32 Bit/Channel. The display will show an approximation of the file; don’t be discouraged if the HDR approximation looks too bright and the colors appear distorted; downsampling will refine the tonalities and you will have ample data with which to make adjustments later on. Click OK and Photoshop will combine all of the data from the selected files into an HDR, 32-bit/channel file.