During our quest to nail that optimal exposure by capturing the right amount of light we often forget to look at the histogram (not the LCD) to see if our photo is properly exposed. If the histogram is way to the left with a clipping bar to the top, we need to adjust the settings and shoot again - unless dark blacks and shadows are intentionally needed as part of yoru creative intention of your photo. So what are we saying here? Well we are saying that properly exposing your shot should be done in camera and not in Lightroom. In other words, you should not make it a habit of not carefully reviewing your shot and say "what the heck; I can always boost that exposure needle in Adobe Lightroom".
That being said, there are instances where like in events or photojournalism assignments, you need to capture the decisive moment with the least concern of setting the proper exposure. Other examples are when we forgot our settings from previous shoot, shot a batch and went home to realize all our shots are underexposed and it is impossible to re-shoot. Should you toss the photos or try to rescue them? What if you were hired to shoot or your family counted on you to capture those family events special moments? Luckily we have the tools available and for this tutorial I will be using Adobe Lightroom to show you how.
1. Always shoot in RAW
To better achieve post processing results you should be shooting in RAW format. Check this article to see why? If you need to really know why RAW is important you can read all about the RAW here. But in summary, let me briefly explain. RAW is not a compressed file format like JPEG. RAW format comes out of the camera untouched but preserves all the details in the photo file and acts as the digital negative. You can go more that 3 steps above and beyond your exposure needle in port processing if you were shooting RAW without losing any dynamic range elements. You can also change white balance on all photos imported with just a click of a mouse. JPEGs are not as flexible as RAW format and the more you save a JPEG file the more you lose details due to its compression algorithm.
2. Global adjustments - if the whole photo is underexposed
If the whole picture is underexposed by a stop or two, the first thing to do is to take that Exposure slider to the right. Keep an eye on the histogram above it to see where you are in the dynamic range. For further understanding of histograms, you can always refer to this post on "understanding histograms".
If you are using Lightroom, you can press and hold the Option (Mac) / Alt (PC) key while sliding the Exposure, Blacks, Shadows, Whites, and Highlights sliders to the right or left to see if you have washed out areas or not in your photo. Try it once and you cannot live without this hidden Lightroom gem anymore.
3. Local adjustments - if some areas of the photo are underexposed
Save what you can and hide the rest before you give up hope and assume that your shoot is a failure. There are a few local adjustment functions in Lightroom that will help you achieve this like the Adjustment Brush, the Radial Filter, and the Graduated Filter. Let's say you have metered from the sky on a sunset scene, and your foreground is too dark to retrieve using the global adjustment sliders without blowing up the sky, consider creating a simple silhouette of the foreground by dragging this Graduated Filter from bottom to up and reducing its exposure slider to a level where the background becomes near pure black.
Definitely not the best option for this photo, but it is an option worth considering. It might not be what you had intended the shot to be, but that might save the shot and convert it to some other creative composition.
4. Mind the noise
Digital Noise is a typical introduction where Shadows and Blacks were brightened specially in long shutter exposures or at higher ISO settings. Don't freak out because Lightroom has the right slider for that. By going into the Detail panel on the right and boosting Color Noise then Luminance you might be able to bring back the photo to an acceptable level. Just re-add the Contrast level because you might have lost it during the process. Remember, this is about reducing noise and not eliminating it. If you push those sliders to much to the right you will end up with a ghostly effect.
5. Last resort - Black and White
If you have a really bad case of underexposure, and you were not able to reduce noise to an acceptable level in step 4 above, not a problem. In this case, the only solution left to do is to convert your photo to black and white. By converting the photo to black and white you are theoretically able to hide the color noise leaving only the luminance noise in the photograph. While it’s still not ideal, it can still be an option to consider if you don't have any other option left. While at it, increase the Contrast as black and white photos adore contrast.