The Adobe Photoshop Lightroom 3 Book: Correcting Exposure
Correcting an overexposed image
Lightroom has the ability to reveal highlight detail that might otherwise be hidden. You can often recover seemingly lost highlight information by combining a negative Exposure adjustment with the use of the Recovery slider. It may be possible to use this technique on a JPEG image to darken the highlights, but the technique shown here really works best with raw images. This is because Lightroom is able to use all of the luminosity information that's contained in a raw file that is simply waiting to be discovered. In the accompanying example, I was able to recover one and a half stops of overexposure, but in some cases, it may be possible to recover as much as two stops.
- This overexposed photograph was initially processed using just the default Basic panel settings in the Develop module. The histogram shows severe clipping in the highlights, and you can see how there is not much detail in the sky or rocks. A histogram like this can appear disconcerting until you realize that there is more information contained in the image than there appears at first sight. Although Lightroom can work its magic on most images, it will have a limited effect on pixel-based images such as JPEGs or TIFFs. For best results, you can really use this technique only when processing raw images.
- The main treatment for an overexposed photo can be achieved by applying a negative Exposure adjustment. If you drag the Exposure slider to the left, you can effectively recover at least a stop or more of information, and maybe even as much as two stops. The downside is that you will usually end up making the overall image darker. But if, instead, you combine a negative Exposure adjustment with a positive Recovery adjustment, you'll get to see the highlight information that would otherwise be clipped, without having to over-darken the image. In the step shown here, I also adjusted the Fill Light, Blacks, Brightness, Contrast, Clarity, and Vibrance sliders, but the main lightness adjustment was achieved by using a negative Exposure adjustment plus Recovery. As I mentioned on page 275, it is often better to optimize the camera exposure to capture as much of the shadow detail as possible, without overexposing to the point where you are unable to process important highlight information. I will often ignore the camera or light meter readings and deliberately overexpose at the time of capture in order to record the maximum amount of levels information and use the combination of a negative Exposure and a positive Recovery adjustment when processing the image in Lightroom.
Correcting an underexposed image
Underexposed images represent a bigger problem because there will be fewer levels available to manipulate, particularly in the shadows. The Basic panel controls in Lightroom can be used to brighten an image and lift out the shadow detail. But it is important that you work through the Basic image adjustments in the correct order, as described in the following steps. When adjusting the tones in an underexposed photograph, you will notice that the Blacks slider is very sensitive and a small shift of the Blacks can make a really big difference in the brightness of the shadows. In the example shown here, I could have opened the shadows more by setting the Blacks slider to 1 or 2. But by setting the Blacks to 3, I was able to preserve more overall contrast.
- As with the highlight recovery method shown earlier, underexposure corrections should mainly be done by adjusting the Exposure slider first in order to set the highlight clipping. This should be followed by an adjustment to the Blacks slider, and then further adjustments to the remaining sliders.
- In this example, I dragged the Exposure slider to the right, which lightened the image considerably, while preserving all the information in the highlights. I then adjusted the Blacks slider so that the shadows were just clipped and used the Fill Light adjustment to radically lighten the dark shadow areas. I also used the Brightness and Contrast sliders to lighten the midtones and add more contrast depth. Finally, I added more Clarity and Vibrance. What you don't want to do here is adjust the Brightness slider before you adjust the Exposure slider. Although similar results can be achieved using this method, you will end up stretching the shadow tones far more than is good for the image, so for best results you should always apply the Exposure correction before you adjust the Brightness. The end result here is a photo that is usable, considering how dark it was before. However, lightening such a dark original has also amplified the noise, which is especially noticeable in the shadow areas.
Match Total Exposures
You can use this command to match the exposure brightness across a series of images that have been selected via the Filmstrip. Match Total Exposures calculates a match value by analyzing and combining the shutter speed, the lens aperture, the ISO speed at which the photos were captured, plus any camera-set exposure compensation. It then factors in all these camera-set values, combines them with the desired exposure value (as set in the most selected image), and calculates new Lightroom exposure values for all the other selected images. I find that this technique can often be used to help average out the exposure brightness in a series of photos where the light values were going up and down during a shoot, which is probably why the chief Lightroom architect, Mark Hamburg, also liked to describe this as a "de-bracketing" command.
So, to sum up, if you highlight an individual image in the series and select Match Total Exposures, the other images in that selection will automatically be balanced to match the exposure of the target image.
- In this example, I made a selection of photographs in the Library module Grid view, where you can see that some of the photos in the sequence were more underexposed than others.
- I selected the photo with the most correct-looking exposure and made this the most selected, target image. I then went to the Develop module and chose Match Total Exposures from the Settings menu ( [Mac] or [PC]).
- In this Library Grid view, you can see how the exposure appearance of the other photos was now more evenly balanced compared to the Library Grid view in Step 1.