If you’re a photographer confronted by extreme-contrast lighting, you’re typically forced to choose whether the shadows or highlights are more important and then throw the other end of the tonal range under the bus. That’s because your camera’s dynamic range can’t capture the wealth of luminance levels the real world contains. Enter Photoshop’s HDR Pro, which lets you conquer high-contrast scenes by combining the brightness values from a set of bracketed exposures. The result is rich detail in both the shadows and highlights with smooth tonal transitions in between. It takes more effort than a snapshot, but the rewards are enormous.

In the previous article, we looked at how Photoshop’s HDR Toning and HDR Pro commands both work inside the magical (and largely imaginary) 32-bit floating-point editing space to manipulate tones. I also explained how the HDR Toning command is the luminance equivalent of upsampling, since it simply exaggerates the tones in a single image. In this article, we’ll look closely at how the HDR Pro command works something like a multipass scan—or, if you prefer, an oversample in the world of music recording—to make the most of the 32-bit space.

Today’s tip comes from Chapter 33, “High Dynamic Range (HDR Pro),” part of Deke’s exhaustive video course Photoshop CS5 One-on-One: Mastery for lynda.com.

HDR Pro works differently from HDR Toning because you give it scads more information to work with. When you feed it two or more bracketed exposures of the same scene, the HDR Pro utility integrates the luminance levels from of all shots to create a rich continuum of tones that takes advantage of the best parts of each exposure.

Shooting for HDR

Producing a great HDR image is really a compositing technique that involves more preparatory camera technique than most other Photoshop work, but the result can be something that is unmatched by any other method.

HDR processing does not handle movement well. It’s best for still scenes such as landscapes or architectural shots. Three things are required to get great results from HDR Pro:

• A steady camera. If you can, lock your camera down on a stable tripod so that the frames align perfectly. Hand-holding the camera can introduce blur and if the registration is off, the software aligns the frames and crops the image down to the area that all frames have in common.
• Perspective and depth of field cannot shift. Do not change the zoom setting between shots, and use the same aperture setting for all shots.
• Make three or more exposures with 1-2 stop increments, changing only the shutter speed.

One of the easiest ways to shoot your bracketed exposures:

1. Set your camera to Aperture Priority and select an ƒ-number that gives you sufficient depth of field. (The higher the ƒ-number, the greater the depth of field.)
2. Focus.
3. Shoot your first exposure with the default settings from your camera’s light meter
4. Use Exposure compensation to increase or decrease exposure in stops, as needed (e.g. + 1 stop to record more shadow detail).
5. Make an additional exposure, and repeat steps 4 and 5 until you have the desired number of exposures.

Another way to create bracketed exposures:

1. Set your camera to Manual mode.
2. Select an aperture setting (ƒ-number).
3. Focus.
4. Adjust the shutter speed until the exposure meter indicates a good exposure, and shoot one frame.
5. For your brackets, double the shutter speed or cut it in half for each 1-stop increment in exposure. Increasing the shutter speed darkens, and decreasing it lightens, the exposure.

HDR Pro uses the label EV (for Exposure Value) to refer to stops, where EV 0 is the default exposure given by your camera’s light meter. You’ll generally want to shoot several over-exposed brackets and several under-exposed brackets. If your EV 0 exposure is 1/200s at ƒ/16, the shutter speeds for your bracketed exposures might be the following:

• EV -2: 1/800s
• EV -1: 1/400s
• EV : 1/200s
• EV +1: 1/100s
• EV +2: 1/50s

More brackets means more detail and luminance levels for Photoshop to work from, but it can also mean sluggish performance. In fact, performance can become very sluggish with too many images. Depending on how contrasty the scene is, you can get great results with 3-5 exposures.

Load ‘em up

You’re ready to bring your bracketed exposures into the HDR Pro environment in Photoshop. HDR Pro is presented in a utility dialog like HDR Toning, Camera Raw, and the Liquify command. You can select your exposures and bring them in via Adobe Bridge, Mini Bridge, or Lightroom. Select the images and then choose the appropriate menu item:

• In Bridge: Select Tools > Photoshop > Merge to HDR Pro from the menu bar.
• In Mini Bridge: Select Photoshop > Merge to HDR Pro from the Tools icon in the upper right corner of the Content pod.
• In Lightroom: Right-click/Control-click and select Edit in > Merge to HDR Pro in Photoshop from the contextual menu – or – Select Photo > Edit in > Merge to HDR Pro in Photoshop from the menu bar.

You can expect to wait a while as Photoshop loads each file into a layer, checks registration and cropping, and performs calculations; but eventually, you’ll see the Merge to HDR Pro dialog.

HDR Pro has the same methods and presets that you saw in HDR Toning, but many of the presets will work better than they did in HDR Toning. The Equalize Histogram, Exposure and Gamma, and Highlight Compression methods operate in much the same way as they did in our coverage of HDR Toning. The Local Adaptation method is the most powerful and versatile method available, so we’ll focus on Local Adaptation for the remainder of this article.

One thing that may be confusing when you first open HDR Pro is the Mode menu that appears to the left of the methods menu. You should leave it set to the default setting, which is 16 Bit, not 32 bit. HDR Pro is working in 32-bit, regardless of what the Mode menu says.

Using the Local Adaptation method

In HDR Pro, the Local Adaptation method has two additional features that are not available in HDR Toning. They are Remove Ghosts and the Tonal Response Curve. We’ll look at those features shortly.

1. Start your local adaptation adjustments by neutralizing the settings, as shown here. (If you saved a preset from the HDR Toning article, it will work here.)

2. Zoom in to 100% and adjust the Radius and Strength values as needed.
3. Zoom out to adjust Gamma and Exposure.
4. Zoom in to adjust the Detail setting.
5. You can try adjusting the Shadows and Highlights sliders, but be aware that they often produce disappointing effects.
6. Activate the Color tab to adjust Vibrance and Saturation as needed.

Dealing with ghosting

If something in your scene moves as you shoot your bracketed frames, oddly-shaped colored artifacts known as ghosts will appear in your HDR preview. By movement, I mean anything that doesn’t appear in the same position in every frame, even pools of light that can shift or change shape with the movement of the sun or disappear because of clouds passing over. Here’s how to deal with them:

1. Turn on the Remove Ghosts checkbox
2. Photoshop will search the frames to select a reference frame. A green border will appear around the selected reference frame in the filmstrip.
3. If you don’t like the result, click a different thumbnail in the fillmstrip to select it.
4. Try as many different thumbnails as you like, until you find the one that produces the best result

By the way, if you’re wondering how a particular exposure is contributing to the overall result, uncheck the box beneath the thumbnail to temporarily remove it from the HDR mix.

Why the HDR Response Curve is different

It’s rare that you’ll be able to get a reasonable result applying a Response Curve to the neutral settings that you started out with. Like the Curves control in Camera Raw, the Curve tab in HDR pro applies its adjustment on top of the tone and detail settings that you should select before you try to adjust the Response Curve.

The Response Curve in HDR Pro doesn’t behave like the Curves dialog you’re used to. That’s largely because it has to represent an enormous, exponentially larger volume of tonal information. First, remember that the HDR space also contains tones that are darker than pure black (0) and lighter than pure white (255). So, using the 0-255 scale for input and output values doesn’t work; the Response Curve uses percentages instead. You also have to change the way you adjust the curve to deal with those sub-black and super-white values.

We’ll look at how you adjust the curve shortly, but first it’s worth taking a moment to explain what’s happening a bit further. As you go from 8-bit to 16-bit to 32-bit editing, it’s easy to think that the number of luminance levels doubles each time, but that’s not what happens. Instead, the number of luminance levels gets squared each time. Working with 32-bit data is really quite abstract (as if 8-bit editing isn’t), and ther’s an additional wrinkle, because your computer’s graphics card and display are 8-bit devices. That means you can only see 256 tonal levels on your screen.

• Imagine standing in a showroom with 256 chairs in it. You can see every chair within the room, and move luminance values between any of them. That’s essentially what 8-bit editing is like.
• When you edit in 32-bit you’re still working with the 256 chairs in the showroom that you’re standing in, but it’s at the center of a gargantuan cluster of 256-chair rooms, containing a total of more than four billion chairs.
• 32-bit editing allows you to teleport out of the showroom to move luminance data around in other rooms. You can also teleport back to the showroom with luminance data from any other room and place it on one of the showroom chairs.

What’s the practical application of this, and how does it affect editing in HDR?

• When you work in 8-bit mode, you’re dealing with hundreds of luminance levels. An 8-bit number can hold any value up to 2 to the eighth power, which is 256. We see 8-bit values all over Photoshop: You could say that any adjustment that has a range of values between and 255 is based on an 8-bit number; almost.
• When you work in 16-bit mode, you’re dealing with thousands of luminance levels. But, Photoshop translates 16-bit values to an 8-bit numerical scale for most controls. The controls still read -255, but a 16-bit number can actually have any of 2¹⁶ possible values. Speaking in terms of tones, that’s 256 x 256, or 65,536 luminance levels.
• When you move from 16-bit to 32-bit mode, the number of levels gets squared again, resulting in 65,536 x 65,536 (2³² or 4,294,967,296) luminance levels! You’re now dealing with billions of luminance levels.

Using the Response Curve

So, how do you use the Response Curve in light of this? The strategy is to add points to the curve so that the shape of the curve surrounds an area inside the densest part of the histogram.

The resulting shape will look as if you have surrounded a set of tones with a lasso. You’re slicing out a tiny piece of that luminance-rich 32-bit universe and mapping those tones into a 16-bit (or even 8-bit) tonal range.

Save and return to Photoshop

Once you have a set of adjustments that work well for one image, there’s a good chance they will serve as at least a solid starting point for adjusting other HDR images. You can save your settings for future use. There are two fly-out menu icons at the upper right corner of the dialog. Select Save Preset from the top menu (immediately to the right of the Presets menu).

Now, you can exit the dialog and return to Photoshop:

• Click OK to transfer the HDR image to Photoshop.
• HDR Pro will now “bake” the final result and produce a flat file.

When HDR Pro is done, the layers it first loaded will be merged and flattened into a Background layer. If you want to redo the image with different settings, you’ll need to start over from the original source images in Bridge, Mini Bridge, or Lightroom.

From here, you can apply any of the techniques we’ve looked at in earlier tech articles:

• Unlock the Background and convert it to a Smart Object
• Sharpen with a Smart Filter
• Convert the image to a toned polychrome

Even though people often think the look of HDR images is somewhat surrealistic, HDR Pro can be used to produce rich images that actually look quite “straight,” but with far more detail in both shadows and highlights than you can produce with any other method. With a little practice, you’ll be amazed at what you can produce.