Increasing Dynamic Range of a Photograph

There are times when it is impossible to capture the entire dynamic range of a scene in a single image. Recently I ran in into this problem during a short trip I made through a beautiful farming valley. I found a lovely old shed and decided to stop and photograph it. After securing permission from the landowner I reached into my car to grab my gear. It was at that moment that I realized that I didn't have a tripod with me. Holding the camera in my hand, I dialed in the exposure for the scene. I quickly realized that the intensity of light was just outside the dynamic range of my camera. Normally if I had a tripod, I would shoot the scene several stops over and under without too much fuss. Later I could then combine the images in Photoshop using layer masks or the Merge to HDR feature. The histogram below shows the exposure of the image as I saw it.

As you can see, the exposure is slightly outside the dynamic range of my camera. The histogram is slightly blocked on both sides of the scale. Important shadow detail resides on the left side while the hightlights are located on the right side of the scale. Without a tripod, I was left to decide if I wanted to expose for the shadows (where all the little details were) and blow out the sky or expose for the brightness of the sky and allow the barn go dark. Is there way to get the best of both worlds in a single image? Sure there is! That's what I love about digital photography (and shooting RAW images)!

Fortunately for me, the light falling on the scene wasn't too far outside the dynamic range of my camera. The sun was high and to my left. I kept a close eye on my in-camera histogram as I photographed the shed. Since I shoot everything in RAW, I knew I could recover a stop or two in both directions later on in processing. With this in mind, I made sure my exposure curve was as close to the center of the histogram as possible.

In this quick tip, I am going to show you how to extend the dynamic range of a single image by processing the shot several times in Photoshop. Understanding how to extend the dynamic range of an image using layer masks has been the bread and butter of my landscape photography.

Watch Your Exposure in the Field

The process starts in the field. If you know you are facing a challenging lighting situation, consider exposing for bright side of the dynamic range. It is difficult (and sometimes impossible) to recover detail in underexposed shadow areas (especially if they have gone completely black). Increased digital noise is a common byproduct of extreme attempts at recovering shadow detail in Camera Raw or Lightroom. Shooting slightly bright should help you capture subtle details in the shadows and make it easier to process later on.

Working in Photoshop or Lightroom

Once you have imported the image, open it in Camera Raw. I usually start by recovering the highlight detail. Make adjustments to the Recovery and Exposure sliders until the right portion of the histogram backs away from the right side wall. In some cases, you may not be able to recover all of the highlights of the scene. Don't worry if you can't recover detail in areas of the image where there are extreme reflections (such as glints reflecting off metallic objects) or bright areas of the sky (such as the sun). Once you have adjusted the overall exposure, it may be necessary to increase the Fill and Brightness sliders to brighten up the image. Adjust the brightness to suit your taste. The histogram and the highlight preview option help to give you an idea of how much detail you have recovered. To see where you are clipping detail, hover over (or click on) the little triangle located in the top right corner of the histogram in Camera Raw. This also works in Lightroom. As you hover over the triangle, red will show through in areas of the image where the highlights are clipped. Don't worry if the image seems too dark after making your adjustments - just do what you can to recover the majority of the highlights. With this image, most of the important highlights were in the sky.

After recovering the highlights (and regaining detail in the bright areas of the image), click and hold ALT (PC) or Option (Mac) in Camera Raw. You should notice the Open Image button change to Open Copy. Select Open Copy to process a duplicate copy of the image. Camera Raw will close and the image will open up in Photoshop. Now go back to the original RAW image in Bridge and open it again. The image will open a second time in Camera Raw. Now we are ready to reprocess the image - this time for shadow detail.

Just as with the highlights you can see where you are clipping the shadow detail. Hover over the little triangle located in the top left corner of the histogram. As you hover over the triangle, blue will show through in areas of the image where the shadows are clipped. Increase the Exposure slider and decrease the Blacks slider until you have recovered the majority of the shadows. As with the highlights, adjust the Brightness and Fill settings to suit your taste. Once you have finished, open the second version of your image in Photoshop.

Bring the Two Images Together

At this point both versions of the image should be open in Photoshop. This is where the fun begins! Pick one of the images and drag it on top of the other using the Move tool (M). Click and hold the Shift key while moving the image to keep it centered. You can close the second image once it has been moved onto the base image.

For the sake of this section of the guide let's assume that you placed the darker image (processed for the highlights) on top of the lighter one (processed for the shadows). Make sure the top layer is selected and go to Layer -> Layer Mask -> Hide All to create a black layer mask. Another way to create a black layer mask is to click the layer mask icon (located at the bottom of the layers pallet) while holding down the ALT (PC) or Option (MAC) key. While working with layer masks remember that black hides and white reveals. Since you just created a black layer mask, the top image should no longer be visible (although it's still there).

Using Layer Masks

There are several ways to merge the two images. Typically I grab a fuzzy white paintbrush and start painting in the shadow detail. Be sure that the black layer mask that you just created is selected before you start painting. For the image of the shed, I painted in the sky. I was careful to ever-so-slightly overlap the horizon (which separated the sky from the foreground). After roughly painting in the sky, I increased the hardness of my paintbrush (with the brush tool selected, right click anywhere on the photograph and adjust the hardness slider). With a moderately hard brush, I painted in along the roof line of the shed. An alternative to using a paintbrush is to make a selection along the horizon and roof line and then fill it with white (to reveal the sky). Using this method still requires that you come back with a soft paintbrush to fine-tune the transition. You can turn down the opacity of the white paint brush to tone back how much is revealed (the opacity slider for the paint brush can be found at the top of the tool bar). With careful painting, it is fairly easy to create a natural transition between the two images. The key to making good transition is patience.

The Blend If Option

Another quick way to blend two images is to use the Blend If tool in the Layer Style dialogue box. With both versions of the image open in Photoshop, drag the lighter image adjusted for the shadows on top of the darker one. Next double click on the top layer to open the Layer Style box. You can also access the Layer Style dialogue box by going to Layer -> Layer Style -> Blending Options (make sure the top image is selected).

With the Layer Style box open, look for the Blend If tool (located near the bottom of the box). We are going to adjust the top slider. Grab the right triangle and gently drag it toward the center. As you move the slider, you should see the lower layer (the darker image processed for the highlights) begin to show through. Once you are fairly satisified with the results, press and hold the ALT key (PC) or the OPTION key (Mac) while pulling on the slider to fine-tune the transition between the two images. Before you select Ok, change the Blend Mode to Lighten.

Quick Note: If the darker layer is on top of the lighter one, simply move the left slider toward the center and change the Blend Mode to Darken (just the opposite).

Keep in mind that you will probably still have to use a layer mask and a soft paint brush to smooth out the transition. You can do that by creating a white layer mask and painting on the mask with a black brush.

You Did It!

You just extended the dynamic range of a single image! Now process the newly combined composite as you normally would. In this photograph I adjusted the curve (to improve the overall contrast), performed some selective dodging and burning, fine-tuned the saturation and applied a sharpening filter. Remember that this process is even easier to work through if you have more than one image. Using a tripod makes it a snap to take several photographs of the scene at varying exposures. You can combine two, three or more images together in Photoshop using layer masks.

Have Fun!

Sure it way easier to use the Merge to HDR feature in Photoshop or a third party program to extend the dynamic range of an image; however I think you can achieve a much more natural look using layer masks. Layer masks provide a huge level of control over every part of the image and let you decide what to hide and what to reveal. Be creative and have fun!

Source: http://www.picturecorrect.com/photographytips/208/increase_high_dynamic_range.htm