The Art of HDR Photography Part 1By Uwe Steinmueller

Dynamic Range and HDR

Fort Point Arcades. High Dynamic Range (HDR) photography is all about dealing with the dynamic range of the scenes we capture, and the limited abilities of our cameras/printers to properly capture scenes such as shown above.

Let's start with a basic definition of Dynamic Range:

Dynamic range is defined by the ratio of darkest and brightest element that matter for your photographic view (measured in brightness levels).

This is not an absolute range, as it very much depends on your personal goals. There are great photos that show very dark shadows without any details; in doing so they represent only the lower dynamic range part of the scene.

There are actually different types of dynamic ranges to consider:

Scene Camera Output (screen, print) Human vision

During the photographic process the dynamic range gets transformed twice:

Scene > Capture Device (here we think of cameras) Capture > Output (monitor or print)

It's important to remember that any detail that gets lost during Capture can never be recovered (something we'll cover in more detail later), but in the end it only matters that the final output image pleases your vision.

Different Types of Dynamic Range

Dynamic Range of the Scene

What are the brightest details and darkest details that you want to portray? This is your artistic decision. Probably the best way to explain is to look at some example scenes.

Lost Cabin: In this scene we wanted to show inside and outside details.

Fort Point Arcades. Again we want to show detail in the bright and dark areas. In general we consider highlight areas to be more critical than shadows. Major blown out highlight usually look bad in prints (show as plain paper white).

A dynamic range (contrast ratio) of 1:30000 can easily be reached in these situations - even more if you photograph a dark room with windows to a bright outside scene.

Ultimately, HDR photography is all about creating pleasing images in these circumstances.

Dynamic Range captured by the Camera

If our cameras could capture high dynamic range scenes in a single shot we wouldn't need the techniques described in these articles. Unfortunately the dynamic range of cameras is much lower than many of the scenes they're used to photograph.

How is the DR of a camera defined?

Dynamic Range of the camera is measured from brightest details to shadows that have good detail well above the noise floor.

The key thing here is that we measure from highlight details (not a pure white) to shadow details that are not degraded by too much noise.

Today's normal DSLRs can capture 7-10 f-stops (1:128 to 1:1000). We don't try to be too optimistic here. Don't get caught up by numbers. Some photographs can look still great with a lot of noise in them and others may lose their beauty. It is your decision. Of course the print size matters too.

Slide film 6-7 f-stops Negative film about 10-12 f-stops Highlight recovery in some RAW converters can gain up to +1 extra f-stop

DSLRs have got much better over the last few years, but don't expect miracles. There are some specialized cameras that can capture a higher dynamic range, but these are mostly cameras designed specifically for very special applications. The Fuji S5 (discontinued), for example, had a unique sensor with dual photo sites that allowed it to capture about 2 f-stops more DR.

Output Dynamic Range

Of all the stages in the digital photography process, the output normally shows the lowest dynamic range.

Today's Monitors: 1:300-1:1000 HDR monitors 1:30000 (watch your eyes, may get stressed) Printers on glossy media: about 1:200 Printers on matte fine art papers: below 1:100

You may well be asking yourself why would it make sense to capture the higher dynamic range of a scene if the output DR is so limited? The answer is dynamic range compression (you'll also see us refer to this later as tone mapping).

Important aspects of Human VisionBecause we present our work to other people it is also important to understand some basic aspects about how we perceive images and the world.

Human vision works in quite a different way to our cameras. We all know that our eyes adapt to scenes; when it gets darker our pupils open, and when it gets brighter they close. This process often takes quite a while (it's not instant). It is said that our eyes can see a Dynamic Range of 10 f-stops (1:1024) without adapting the pupils and overall about 24 f-stops.

Contrast

All detail we can see is not based on absolute tonal values but based on contrast at some image edges. The eye is extremely sensitive to very small contrast changes. This makes the concept of contrast so important.

Global Contrast

Global contrast measures the brightness difference between the darkest and brightest element in the entire image. Tools like Curves and Levels only change global contrast as they treat all pixels with the same brightness identically.

The global contrast has three main regions:

Mid-tones Highlights Shadows

The sum of the contrast of these three regions defines the global contrast. This means if you spend more contrast on the mid-tones (very common) you can spend less global contrast on highlights/shadows at any given global contrast (e.g. glossy paper print).

The mid-tones normally show the main subject. If the mid-tones show low contrast the image lacks "snap". Adding more contrast to the mid-tones ("snap") often results in compressed shadows and highlights. Adding some local contrast (see below) can help to improve the overall image presentation.

Local Contrast

The following chart helps to understand the concept of local contrast. The circles in each row have exactly the identical brightness levels.

Yet the top right circle looks a lot brighter than the one on the left. Why is that? Our eyes see the difference between it and its local surroundings. The right circle looks brighter with the dark gray background compared to the same tone on a brighter background on the left. Just the opposite is true for the two circles on the bottom. For our eyes the absolute brightness is of less interest than the relative relation to other close areas.

Tools like Lightroom's Fill Light and Sharpening, and Photoshop's Shadow/Highlight act locally and do not treat all pixels with the same brightness value identically.

The classic Dodge & Burn tools manipulate the local contrast of images. Dodge & Burn is still one of the best methods to refine images, because our own eyes are naturally pretty good at judging how the image is going to appear to other people's eyes. In some way today's tone mapping tools reduce the need for manual dodge & burn without replacing it.

HDR: Managing Dynamic RangeWhy then even bother to photograph scenes with higher DR than your camera's or printer's DR? The answer is that we can capture the scene's high DR and later map it to a lower DR output. The key point here is that we don't lose any detail information during this process.

There are other solutions to the problem:

Some photographers simply wait for overcast conditions, and don't photograph at all when the DR of the scene is too high.

Use fill flash (which of course does not help with landscapes)

While on a longer travel trip you have to get the best out of any weather and we need to find better solutions. Also often the existing light may not depend so much on the weather. This is best illustrated with some example images.

Page Antelope Canyon. This scene in Antelope Canyon is very dark, yet there is still an amazingly wide dynamic range of light (we used 5 shots here at 2EV apart).

Alcatraz. In Alcatraz the light from the right was still quite bright compared to the dark room (there was no artificial light available).

The first step is to capture the full DR of the scene with our cameras without losing any details.

Mapping DR: Lower DR Scenes

Lets first have a look at photographing a lower DR scene.

Lower DR Scene

In this case we can capture the DR of the scene directly with our cameras in one shot. The minor clipping in the shadows is not usually a problem.

Next we map this captured tonal range to our output (which usually offers even lower DR than the camera itself).

Mapping to Output

Mapping to Output

The mapping from camera to output is mainly done via tone curves (often compressing the highlights and shadows). Here are the main tools that get involved:

Raw converter processing: maps from linear camera tonality via tone curves Curves and levels in Photoshop Dodge & Burn in Lightroom or Photoshop

Note: In the days of the wet darkroom we printed negatives with enlargers and used papers at different grades (or multigrade papers). The grades differed in the contrast they produced. This is the classic method of tone mapping. Tone mapping may sound like something new, but it is far from it. Only in the early days of photography did photographers map directly from scene to output. Since then the sequence followed has always been:

Scene --> Capture --> Output

Mapping DR: Higher DR Scenes

Now let's look at the situation when we photograph a higher dynamic range scene.

Clipping in Highlights and Shadows

Here is an example how the result could look:

As we can see the camera can only capture part of the scene's dynamic range. As mentioned earlier, it's rare that clipping the highlights is a valid option. This means we need to change the exposure to protect all the highlights from getting clipped (ignoring the specular highlights, such as reflections). Then we'd have the following situation:

Exposed for the highlights

Now we have stronger clipping in the shadows. In some cases this may be perfectly fine, though not if we want to show more shadow details.

Below is an example of how the result of exposing for the highlights might look:

Capturing Higher Dynamic Range with Bracketed Exposures

So how can we capture all the DR we want with the same camera? The solution is to capture multiple overlapping exposures at different EV (Exposure) levels.

Exposure Bracketing

Exposure BracketingIn HDR photography we capture multiple different, but overlapping, exposures to cover the DR of the scene. In general the exposures differ by 1-2 EV. This means the total number of needed exposures is defined by:

The DR of the scene we want to capture

DR the camera can capture in a single shot

Each additional exposure can add 1-2 EV (depending on your selected bracketing) of DR to the camera's DR.

Now we have to find out what we can do with these multiple exposures. There are quite a few methods:

Manual blending (today in Photoshop, was/is done with enlargers) Automatic Exposure Blending (Fusion) Creating HDR images (in HDR enabled Software)

Manual Blending

Manual blending of different exposures (using what are essentially montage techniques) is nearly as old as photography. Even if Photoshop makes it much easier these days it can be a tedious process. We hardly ever use manual blending.

Automatic Exposure Blending (also called Fusion)

Here the software (I most often use Fusion in Photomatix) performs the blending process by blending the different exposures directly into the final output image.

Exposure Blending

Exposure Blending

Fusion (Exposure Blending) usually produces very nice images that look more "natural".

Bryce Canyon blended with Fusion

Creating HDR imagesHDR processing is actually a two step process:

Create a HDR image Tone-map the HDR image to a normal 16 bit image

When creating HDR images we actually follow the same goal but use a different way. With HDR Imaging (HDRI) we first merge the images to an HDR image and do not map directly to the final output.

Creating a HDR image

Something entirely new to photography (they cannot exist without computers), HDR images are 32-bit floating point images that can store a practically infinite dynamic range of tonal values. The HDR merge process tries to find all the tonal values in the bracketed exposures and create a new electronic image that represents all the tonal values captured by all the exposures.

Note: Always if something new comes along some claim this is an old hat and they did this before they were born :-). To make it clear, HDR processing as described here is new and can only be done using computers, and over the past few years the results have become more and more usable.

But we photographers are only interested in the final print, and techniques to reach this goal existed long before we had computers. In the movie industry they actually work with the HDR images during the CGI process (e.g. 'lets add a second floor to a building'). For photographers, HDR is just a step on our way to the final print. And, again to make it clear, new technology does not automatically produce better images. HDR is simply a new tool that we can exploit and use to create images that were harder to achieve in the past.

Why create images with high dynamic range at all, if the output DR is so limited?

Answer: Tone mapping - Map the tonal values from HDR to Output DR

That is why tone mapping is the most important - and also challenging - part of HDR processing for us photographers. The same HDR image can the tone-mapped in many different ways.

The HDR images also can be stored in different formats:

EXR (.exr suffix, high color gamut and precision, DR about 30 f-stops) Radiance (.hdr suffix, less color gamut, huge DR) BEF (private format by Unified Color to get better color quality) 32 bit TIFF (very large files due to low compression and not much used in practice)

To create these HDR images you need special HDR software. We use:

Photoshop CS5 HDRsoft's Photomatix Unified Color's HDR Expose or Express Nik Software HDR Efex Pro 1.0

Unfortunately all these different software packages produce different HDR files. They can differ by (we'll cover these aspects in more detail later):

Color (Hue and Saturation) Tonality Alignment Noise handling Chromatic Aberration (CA) handling Ghosting reduction

The Basics of Tone Mapping

As with our Low DR Scene case, we need to compress down to the output DR:

Mapping down to Output DR

How is this different to the Low DR Scene situation? This time the tonal compression is much stronger, and the classic tone-curve approach doesn't work that well anymore. The easiest way to show the basic tone mapping principles is to use an example:

3 Exposures at Fort Point

These are dark arcades at Fort Point in San Francisco. To demonstrate the tone mapping principles we'll use Unified Color's HDR Expose tool, because it allows us to use the various different operations involved in a modular fashion.

Here is the merged HDR file shown without any changes:

HDR Image

It's pretty dark in the shadows, and also almost totally blown out in the highlights. Lets take a look at the histogram as shown in HDR Expose:

Histogram of the HDR original

The shadows are not really a problem, but the highlights are clipped by about 2EV. First we'll see how a minus 2EV exposure correction would improve the image:

-2 EV Exposure Compensation

-2.0 EV histogram

Now the highlights seem to be much better but the overall image looks way too dark. What we need is a mix of exposure compensation and lowering the global contrast.

Global Contrast reduction

The global contrast is now fine. No highlights are clipped and the shadows are open. Unfortunately the image looks quite flat.

In pre-HDR days, the solution for such a situation would be to use an S-Curve in Photoshop:

Simple Photoshop S-Curve

But crafting a good S-Curve would take a while, and could easily result in over compressed highlights and shadows.

This is why tone mapping tools take another route: They improve the local contrast.

Global and local contrast changed

In this version the highlights show detail, the shadows are not blocked and the flatness is gone. This would be not our final version. We usually optimize the photo in Photoshop CS5:

Tuning saturation Optimize Contrast with DOP Contrast Plus V2 Final sharpening with DOP Optimal Sharp

Note: In Unified Color's HDR Expose you actually can control the global and local contrast independently. We like this systematic approach, as we understand the settings in photographic terms.

What makes all the HDR tools different is the algorithms they use to deal with lowering the contrast (e.g. how they deal with what should be "local"). There is no right or wrong, and it is more a question of your own preferences and personal photographic style.

All the main HDR tools in the market also offer control over further parameters:

Detail: Very much related to local contrast and sharpening but not quite the same. Too much detail can make images "grungy". This can be what you want or just not. We use normally our DOP Detail Extractor V2 script for very strong detail.

Saturation: Except of HDR Expose and Nik HDR Efex Pro (via U-Points) most HDR tool handle only global saturation (all colors treated the same)

White Balance (WB): we try to solve this already at the Raw level in Lightroom (or other Raw converters). Noise Removal: again we remove the noise in Lightroom 3.x if needed. Shadow/Highlight: treatments to open shadows and toning down highlights. Curves: The Curves in Photoshop CS5's Toning (The new CS5 Tone-Mapper) are powerful, but require some time to get

the right result.

We'll cover most of these aspects later in the HDR Workflow and HDR Tools chapters in more detail.

Summary on Dynamic Range and HDRThe approach to enhancing the dynamic range that your camera can capture is very old, because these limitations have been known about for a long time. Manual or automatic blending of images offers very powerful ways to map the combined dynamic range of your images down to the lower dynamic range of your printed output. Creating seamless blended images manually can be very challenging and time consuming: Dodge & Burn are techniques that can be very powerful for creating good print, but they require practise and perseverance.

Creating HDR images is a new way to master the same old problem. We as photographers are mostly interested in the tone-mapped results. Tone mapping algorithms face the challenge of compressing a high dynamic range down to an image we can view on a monitor or in a print. The various different methods of tone mapping can give very different results, and it is up to the photographer to select methods he likes best.

The Art of HDR Photography Part 2By Uwe Steinmueller

Chapter 2: HDR ChallengesSee also Chapter 1: Dynamic Range & HDR

The Ghost of Grafton

To better understand the "Essential HDR Workflow" we need to understand some of the challenges we face creating HDR photos.

Terminology

Ghosting

Since we're taking multiple photos, we don't only have moving elements in a single shot to deal with: any elements that move from between shots will appear "ghosted". The image below shows such a situation.

Person moved while shooting all frames

Note that in this case the ghosting was intentional. Ghosting is not always a bad thing; it always depends on your own goals with your images. That said, generally speaking we try to avoid ghosting as much as we can.

Chromatic Aberrations (CA) and Fringing

Chromatic Aberrations (CA)There are several different kinds of Chromatic Aberrations, but here we dealing mainly with Lateral Chromatic Aberration, as it can be reduced using raw development software. Lets first show an example:

CA shows most often as Red/Cyan fringes but it also can be Blue/Yellow. CA is a lens property and all lenses have this defect to some degree. The further you get from the center of the frame the more the different light frequencies focus differently on the image plane. The lens manufacturers try to correct CA and different lenses show a different amount of CA (Wide angle lenses and zoom normally show stronger CA).

Nearly all raw converters can reduce CA to some extent. Many years ago the French company DxO started to correct CA (and other lens deficiencies) automatically, based on the lens and camera information. Also the latest versions of Lightroom 3.x and Camera Raw 6.x (ACR) allow automatic CA corrections as part of their lens correction feature (uses camera/lens profiles). Here is how Lightroom 3.3 showed the corrected image:

So why do we care so much about Chromatic Aberrations?

1. The latest high resolution digital cameras resolve more and more of the CA that our lenses produce.2. But more importantly CA gets amplified when we merge images to HDR, multiplying all the CA of the

different exposures. There are also cases where we see 'purple fringing' that may be related to sensor leaking between the pixels. It shows at high contrast edges. Lightroom and ACR have a "Defringe" option that also helps to reduce fringing a bit.

HDR Challenges

HDR Challenge: Motion

Since we're taking multiple photographs movement is even more of a challenge than it is with single shots. Basically we deal with two types of motion:

Camera motion Motion in the scene

Camera Motion

For each single shot you need to take to avoid camera shake. On top of that you also want to make sure that there is no motion between the shots.

a) Using a Tripod

The tripod, head and plate need to be sturdy Use a remote to avoid introducing shake to the camera Use mirror lockup or live view to minimize mirror slap

Note: Some photographers assume that there is no camera movement between shots if they use a good tripod. You will be surprised how much the tripod gets rattled by most camera mirrors and shutters. Even very minor movements can degrade the final HDR quality (if the images do not get perfectly aligned, more on which later).

Exercise: Try to use a 200mm lens from your tripod and experience the misalignment you get.

b) Handheld

It's worth noting that we personally shoot a lot of HDR images handheld.

The key thing here is to use fast shutter speeds and utilize camera/lens image stabilization. The most critical exposure is the most overexposed frame because it has to have the slowest shutter speed.

The best approach is to use the highest continuous frame rate your camera can deliver. The ideal burst rates for the purposes of handheld HDR are 7-10 fps, but we also use slower cameras down to 3fps (in this case the demands for steady alignment are higher though). High frame rates ensure that the camera moves less between shots, and will reduce visible movement (ghosting) within the scene.

Perfect Alignment

It should be clear by now that the key to the best possible results lies in the perfect alignment of all the images shot. In the Essential HDR Workflow chapter we'll share our personal technique to archive this goal. Here is an example what software alignment can do.

The following image shows how bad the images were aligned as shot (the image shows the different layers showing through).

Strong Misalignment

OK, this was shot handheld. Ah, we hear people saying; we told you use a tripod. But this was shot on a Pacific cliff in a very strong wind. In this case shots using a tripod could well have be even worse, and would not have allowed us to shoot at the angle we wanted. In the worst case both camera and tripod could have been blown into the ocean! Here is what Photoshop could do with it:

Aligned in Photoshop

As this example clearly shows, software image alignment is crucial for most HDR work, especially given how difficult it is to get 'perfect' shots every time. We'll get into more practical detail in our next chapter.

At first glance you might think that aligning images using software is a relatively simple task: you just shift the image a bit until it lines up - and in fact this is some implementations actually work. But, naturally, it's never that simple. The camera can move in many ways:

left/right/up/down Front/back (means each shot shows a slightly different magnification)

Rotate Tilt Any combination of the above On top there are also lens distortions which make it even more complex

Remember all misalignment (whether major or not) degrades your final image resolution; all your expensive Mega Pixels are easily wasted.

Here is an example of poor alignment:

Poor Alignment

I should mention that thus far we haven't usually named or recommended specific software packages. For one thing this is because the various options all improve over time, for another it very much depends on the images used (there is no universal solution). In a later chapter we'll show a method that helps us to get consistently good results.

Often you realize very late in your workflow process that the alignment was less than optimal (the above sample is of course easy to spot) It may be very subtle but we aim always for best possible alignment.

Alignment in Photoshop CS5

Motion in the SceneCompared to misalignment issues, motion within the scene is far harder to correct (using processes sometime referred to as 'de-ghosting'). You will be surprised how many things move. Motion in the scene means mostly movement between the bracketed shots, and the faster you shoot (i.e. the shorter the time between shots), the fewer elements in the scene can move. Just a few of the potential 'movers' in scenes are listed below:

People and larger animals Cars and other transportation devices Foliage Birds, Butterflies Flags Clouds Water

Lets have a closer look at some of these elements.

People and animals

The good news is that these are often easy to spot, allowing you to take them into account at the point you're actually taking your photos. The bad news is that ghosting created by moving people (and larger animals) are also tough to remove, so the best solution is to analyze the scene carefully while you shoot and avoid them completely if at all possible. Some ghosting in the background (distance) is often perfectly acceptable.

Cars and other transportation devices

Being large, these are equally problematic, but typically are moving a lot faster, meaning you should be able to keep them out of at least some of the frames. Don't try HDR for fast sport :-).

Foliage

Foliage is extremely tricky because:

It's easy to forget about and hard to combat It can result in nasty HDR artifacts

This means that you have to watch any foliage close to the lens and in focus, as it may cause trouble.

Birds or big Butterflies

Ghosting of birds or butterflies that fly through the scene look often like sensor dust, so we treat them just like dust (i.e. we remove them using Photoshop's healing brush). Of course if the bird(s) are important to your image you may try some of the de-ghosting options in recent HDR software.

Flags

Flags are so common that they are deserve their own category. We recently tried the de-ghosting option in Photoshop CS5 and the result was quite impressive:

Without de-ghosting With de-ghosting

Clouds

We don't consider most clouds to be a problem because their ghosting looks just as organic as the original clouds. Of course extremely fast moving clouds can cause some problems. We recently saw some purple artifacts in the clouds using Merge to HDR in CS5. Enabling the de-ghosting feature took care of it.

Water

Slow moving or still water (such as creeks and lakes) rarely causes any problems, but we haven't had much luck with strong ocean surf. Trying one of the de-ghosting options may improve the images.

HDR Challenge: Chromatic Aberrations (CA)

In the introduction of this chapter we explained that CA is a major problem for HDR. The best approach is to remove as much CA as possible in your raw converter. Although some HDR tools can remove CA in the Merge to HDR step, and it helps, we personally try to remove it before merging to HDR.

HDR Challenge: Camera Noise

As mentioned in the last chapter, camera noise is a limiting factor for the dynamic range of our cameras, and the reason to use exposure bracketing is to overcome this limitation. But once we start producing HDR images, we tend to open up the shadows (during tone-mapping) more than we ever did with standard processing. This again reveals the noise. There are, of course, several ways we can minimize the impact of noise on our HDR images:

Use as low an ISO setting as possible Use raw converters that perform good noise removal (e.g. Lightroom 3.x/ACR or DxO). Use noise removal filters on the final tone-mapped image.

HDR Challenge: Source Image Formats (Raw or JPEG)

JPEG. In our personal work we hardly ever use JPEG images. Why?

JPEGs show compression artifacts They are limited to 8-bit color depth, while raw images can have 12-14 bit information. More color depth allows finer

color gradations Inaccurate white balance can degrade JPEG image quality

Less headroom for highlight recovery Lower dynamic range

If you're using JPEGs for HDR the last point isn't really an issue since you can capture higher dynamic range via multiple shots.

If you don't want to deal with raw images, creating HDR images from JPEGs is still a valid technique; you just need to understand the limitations.

Raw. With the Raw images you have access to all the information the camera captured. Actually HDR files and raw images are both linear file formats. To be able to view these images both require the application tone curves.

Here is a practical dilemma. In the ideal world all "Merge to HDR" operations would start with the linear HDR data. Otherwise the HDR tools have to undo the tone curve operations performed by the raw Converters. This is why quite a few HDR tools offer the option to create HDR directly from raw (mostly using the public domain raw converter dcraw).

So why do we prefer to use an external Raw Converter such as Lightroom 3? Simply because we think that in the end these Raw converters allow better control over noise removal, CA removal (e.g. Lens profiles in Lightroom) and lens distortion corrections and offer better de-bayering and custom color profiles (e.g. DNG color profiles via ColorChecker Passport from X-Rite).

We always convert to 16 bit TIFF files before the "Merge to HDR" step, and the loss of quality due to the tone curve reversal seems quite acceptable in practice.

HDR Challenge: Lens Flare

Lens flare degrades image quality in certain shooting situations (such as sunsets). This in itself is nothing new, but with HDR we tend more often to include bright light sources into our compositions, which means flare is more prevalent.

Summary

You need to understand these HDR challenges to get the best possible quality. This list is almost certainly incomplete, but hopefully we've covered the main hurdles you'll face. Feedback by our readers is very much welcome.

Chapter 3: Essential HDR Workflow

By Uwe Steinmueller

Zion Lone Tree

Scene Analysis for HDR"To HDR or not to HDR" is often the question while photographing a scene. Regardless of whether a particular scene requires HDR to accurately capture it's essence, it is pretty much always beneficial to have bracketed photos to work with. Having multiple exposures allows you to chose the best single shot or to go the HDR route. Here is a short checklist to assist you in making that decision.

Moving Elements Here are some situations in which attempting to use HDR techniques would produce unusable results:

People or animals in motion Birds in flight Sports or other high motion activities Foliage in windy conditions Ocean with strong surf (if detail should be visible)

We almost always shoot bracketed exposures. We always have the middle exposure as the first shot and have the option to just delete the other exposures later if we don't need them. The first shot will be the normally exposed shot taken at the moment you hit the shutter. Of course bracketing shots uses more frames and so for fast action should always be turned off to increase responsiveness.

Scene Dynamic Range EvaluationEvaluate the scene for the dynamic range you would like to capture.

Overcast: No HDR needed in most cases (unless you plan to show details in darker shadows). Midday sun with strong shadows: Take 3 shots at about 1 ~ 1.33 EV apart.

Mission San Antonio in California

In these cases a single middle exposure photo often works fine but bracketing for HDR can give you more options for nice highlights and open shadows. As with the photo above we often shoot these scenes handheld, because there is enough light to get a fast shutter speed (even for the overexposed image).

Dark rooms with some light through the windows: Here we usually take at least 5 bracketed shots with about 2EV apart. Using a sturdy tripod is a must.

Fort Point: Officer's Bed

Dark room with detail in bright scene outside the windows: Indoors in low light you may need to bracket for 7 or more exposures. In this situation a tripod is of course is a must. The use of a manual programmable remote control allows you to change the exposure time without moving the camera.

Note: These types of images only pay off if there is an artistic balance between the interior and exterior zones of the image.

Highlight/ Shadow ChallengesAlways make sure you know how to capture the details in the highlights and how to get the shadow details you want. While highlight clipping should always be avoided it is your artistic decision how open the shadows should be.

Tripod/HandheldTwo factors will help you decide wether to use a tripod or not:

Your personal style of photography (tripods are stable but handheld gives you more flexibility). If the most overexposed photo of the set can't be taken without a tripod (without inducing motion blur), the only option

is to use a good tripod or forget about HDR.

Capturing Exposures for HDR After analyzing the scene (which normally only takes a few seconds) you should know how many brackets to shoot. Depending on your personal shooting style you can then decide on whether to use a tripod or shoot the scene handheld.

Bracketing Setup

Normally we rely on the camera's AEB (Auto Exposure Bracketing) feature. Here the camera controls the exposures of all the shoots needed.

Here is how it looks on more recent Canon and Nikon cameras.

Canon 3 shots @+/- 2EV Nikon 5 shots at 1EV apart

Note: It's unfortunate that some camera manufacturers limit some features which would be useful to HDR photography:

Limited maximum EV step of 1EV (in some cases it's limited to 2/3EV). We've pushed for change in our reviews for years but manufacturers have yet to take note.

Limited the maximum number of bracketed shots to 3 photos (except in the higher priced cameras). All cameras we know of limit the maximum exposure time to 30 seconds. I don't believe there's a solid

technical reason for this any more. Yes, I know long exposures can create noise, but many cameras work quite well beyond 30 second exposures. The photo below stressed the 30 second limit quite a bit.

Antelope Canyon

HDR Brackets from the Tripod

For HDR a tripod is even more essential than with single shots, to avoid any movement between photos.

Sturdy tripod, heads, clamps and plates are needed Use a remote if available or the camera's built-in timer Using live view or mirror lockup can reduce camera shake when taking longer exposures.

HDR Brackets Handheld

Software can work very well to align your bracketed images (more later) so in many cases shooting HDR hand-held can work quite well. For these shots we enable AEB for three exposures (usually about 1.33 EV apart). Then we use the highest possible frame rate to capture all three exposures. To decrease motion blur the fastest high speed shooting possible is desired. Using 7-10 frames per second can produce good results but we also use slower frame rates. The camera should be set to continuous shooting and will normally stop once the bracketed exposures are done. We need to keep the aperture constant so we shoot in Aperture Priority mode.

Keep in mind the order of the exposures as well. When shooting we always try to use the following sequence: normal, under-exposed, over-exposed - if possible. This way the normal exposure is the one we capture nearest to the moment we hit the shutter. We set the EV compensation for Aperture Priority so that in many cases the middle exposure can be used as a single shot. The under-exposed shot can be used as a backup in case the middle exposure shows clipped highlights. The last and over-exposed photo has a higher likelihood to show motion blur from camera shake because it uses the longest exposure. That is why it's important to check that the highest possible shutter speed is fast enough for the +1 1/3EV exposure

We nearly always use cameras with lens image stabilization (IS, VR) to get our photos as stable as possible. Hold the camera steady through out all the shots. We will sometimes even take 5 shots, though only with cameras that can do at least 7 frames per second.

White Balance

It is very important to keep the White Balance (WB) the same for all shots in your bracket sequence. However, we still use Auto WB because we only use the camera's Raw image format anyway.

Most often the auto WB will be the same or very close. All Raw converters can easily allow to sync the WB settings in your sequence. This does not cause any perceptible loss

of quality.

If you plan to shoot JPEG for any reason it's best to set a manual WB for your sequence. Remember to check your WB before you shoot your next scene.

More Issues to check for

Avoid to shooting directly into the sun.

This could physically damage the sensor The flare introduced in the lens and camera reduces image quality

High Speed HDRWe've already covered this to some extent in our section about handheld bracketed shooting. In this section we will go more in-depth on high-speed bracket shooting because it can create an entirely new style of shooting in the field.

With the camera set to the highest burst rate (7 - 10 fps) we capture bracketed shots with different exposures at this speed. This means a 3-exposure bracketed sequence (-1, 0, +1EV) is shot in less than a second.

To ensure success using this method make sure the camera exposure is set to aperture priority and watch that the shutter speed is fast enough to produce sharp photos. If it's not you may need to use a higher ISO or a tripod.

As you can see, the basics are very simple. This is important because in the field we want to get as much technique out of our way as possible so you can concentrate on the subject scene.

Why "High Speed bracketing"?We have combined the classic bracketing approach with modern HDR techniques.

Classic bracketingThis proven technique is based on taking multiple shots at different exposure settings to ensure a single best photo. The only difference here is that we shoot these frames so fast that it feels like a single shot (at least once you make it a habit).

Expose to the rightIn essence this well known technique means choosing an exposure that allows you to fully recover all of the highlights. If you only grab one shot it may turn out to be unusable if you are not able to recover all highlights. This is not always easy to check in the field. With our technique we always have the underexposed shot as a solid backup.

Since we're not overly worried about the right exposure (one of the three frames will be good enough) we can concentrate on the scene we're trying to photograph. In the past I've checked histograms all the time and even used manual exposure, but now I more or less leave exposure on automatic (Aperture priority). I only avoid automatic exposures when shooting photos for stitching, when all the frames need to have the exact same exposure.

Using advanced HDR techniques

Because we always capture bracketed exposures we always have the option to use HDR if it would help our final image.

It may sound like my intent is to always merge images to HDR. This is not necessarily the case, but we always have the option to do so if necessary - which is why we call it "Capturing more Light". Using this technique we capture about 2-3 f-stops more dynamic range that we can make use of if need be. If you consider that many of the recent top DSLRs capture about 8-10 f-stops in a single frame we can extend the dynamic range to 10-13 f-stops (this approaches the dynamic range of color negative film).

Analyze the bracketed Exposures Dynamic Range coverage: Check the Histogram

It is good practice to check the camera histogram of your sequence after the shoot.

Under exposed photoIt is important that the under exposed photo has no clipped highlights, otherwise the final HDR image will also show the same clipping. Look for a good amount of head room as shown in

Over exposed photoYou do not want too much clipping in the shadows. The histogram below is acceptable, though more headroom in the shadows may have been better.

the histogram.

Histogram of an under exposed photo. Histogram of an over exposed photo.

Middle exposed photoAs expected the middle/normal exposure falls in between the other exposures. There is not much to check here.

 

 

Histogram of the middle/normal exposed photo

Check for Motion Blur You should also check the images for motion blur. In most cases you will know how these shots pan out at certain shutter speeds based on experience.

Check for moving objectsCheck both while shooting and afterwards for unwanted movement in the scene that might cause a problem.

Raw conversion for HDRWe are assuming that you will capture your images in Raw mode. HDR from JPEGs will work but is often not of the same quality.

White Balance (WB) All shots in the sequence should have the same WB. Correct the WB of the normal exposure in your Raw converter and then synchronize the WB settings to the other exposures.

Chromatic Aberrations (CA) and other Lens CorrectionsWe mentioned before that CA correction is crucial for good HDR images. We can perform this correction using the Lightroom 3 Lens Correction tool:

Lightroom 3 Lens Correction Settings

If your lenses are supported in Lightroom the correction will be applied automatically otherwise you have to use the manual CA corrections. We also set "Defringe" to "All Edges" with the goal being to reduce or remove as much fringing as possible.

Correcting the lens distortions and vignetting is more a matter of preference. However, if you photograph architecture it can be essential.

No major Curve or Basic settings corrections Keep the images as linear as possible. Merging images to HDR works best with linear files because the HDR images themselves store the tonal values in a linear way. All the HDR tools try to recreate the linear data if they work from TIFF files (it's best if you also use 16 bit data here).

Actually "Merge to HDR" in Photoshop ignores these settings to get the best possible results. It is unfortunate this does not work in cases where you need to perform Highlight Recovery (see below).

Highlight Recovery (HR) can save the day

If your bracketed sequence covered the highlights well you do not need to use this trick but every once in a while it can save the day.

We had a chance to take some pictures at the abandoned Gilroy Hot Springs. These hot springs are is a part of Henry Coe State Park, but most of the time are closed for the public. We had hoped for some overcast skies (having started out with an overcast morning in San Juan Bautista) but when we arrived at the Springs we found the worst light possible (10am Summer sunlight). As usual we shot all our photos bracketed and handheld (here a Sony NEX-5 with its very limited EV spacing of 2/3EV). To be honest we thought these images would mostly be a lost cause (especially the image we feature here). Fortunately the Highlight Recovery in Lightroom 3 saved the day.

Basic default setting for linear conversion (all are zero)

Bracketed Exposures with Histograms

As we examine the underexposed photo we can find that even though there is no fatal clipping visible, it is still too much for our taste. Clipping in the underexposed photo cannot be recovered in the final HDR image and results in bad highlights after tone-mapping.

Basic settings with Highlight Recovery

After HR correction

Once we are able to produce an image with good Highlight Recovery for the most underexposed photo we then sync the settings to the other photos in the bracketing series.

Note: You cannot use these settings directly with Lightroom 3 using Edit in > Merge to HDR because in this case Photoshop will bypass these corrections in an attempt to access better data directly from the Raw. You should create TIFF files instead and work with them in Photoshop.

As we mentioned earlier, this saved the day and we got the final result we wanted after merging to HDR and tone-mapping. Still, it's best you take proper bracketed exposures to avoid the need for this kind of trickery.

Noise

As always, shooting at lowest ISO level possible avoids noise. This is rarely an issue if you use a tripod. But, if you shoot handheld you have to balance Aperture, Shutter-Speed and ISO wisely. Because the Aperture is defined by your lens and intended DOF (Depth of Field) you basically have two parameters to work with:

Shutter Speed: needs to be fast enough to avoid motion blur on the most over exposed photo. ISO: Higher ISO shows more noise.

We would gladly trade more noise for bad motion blur which would make the exposure unusable.

Sharpening

It's best not to sharpen before we merge to HDR for the following reasons:

The HDR and tone-mapping process may amplify sharpening artifacts Part of the tone-mapping process also extracts more details Sharpening as final step is often a good practice anyway

Optimal Image AlignmentIn this section we will cover alignment as a a discrete step although most HDR tools include automatic alignment. Unfortunately not all alignment is of equal quality.

We have often found that the alignment in Photoshop CS5 gets the best results, good enough for HDR images of high quality.

We have created a modified CS5 script that you can download for free. The use of this script is at your own risk and does not include any support. This script is only designed to work with CS5. We use this script on our Mac all the time and it should work on Windows as well. You should download this script before continuing with this section as it will be referenced in the process.

DownloadThe script can be downloaded from here (ZIP File). Copy the script to the Photoshop/Presets/Scripts folder.

Merging ProcessThe key to any good HDR merge is a precise alignment of all of the images. Photographers often use very sturdy tripods to shoot nearly perfectly aligned images. In this case the HDR software will have a little bit of work to do to perfect the alignment. Bad alignment may not be that easily visible but can show as a loss in resolution, and all we can do is to use the best alignment available to us. For high resolution HDR images proper alignment is ultra-critical.

Try it: Shoot with a 200mm lens on a very sturdy tripod with a camera such as a Canon 1Ds Mark III or Nikon D3x. Follow all the rules about mirror lockup and remote shutter release. Take 3 shots. You will be surprised how much the shutter alone rattles your camera.

On the other hand we shoot a lot of bracketed shots handheld, at which point the task of alignment becomes more complicated. In our experience there is not much of a problem when you use cameras that can shoot 7-10 fps sequences. However, we often use the Canon 5D Mark II or Canon 550D which can only shoot at about 3fps. In this case we've found that some HDR applications can fail to perfectly align all the shots. Remember you may tilt, shift and/or rotate your camera between shots.

In our experience Photoshop CS5 most often performs the best alignment. You may be asking yourself: "why not create the full HDR image in CS5 too?" Unfortunately not all HDR merging software performs equally (e.g. saturation) so we may want to perform the HDR creation in other applications.

Which leaves the following question: How to align images in CS5 and then merge to HDR in an application of your choice later?

Here we will explain how to do it. It makes the workflow a bit more tedious but is clearly worth the effort.

Three bracketed exposures

Step 1: Settings in Lightroom (or Camera Raw)

We will perform some basic and important corrections in Lightroom 3 (identical for all images in our bracketing sequence).

Highlight recovery if needed Lens Correction (we want as much CA removed as possible) Noise reduction if needed White balance Keep all tone curves linear Black Point to 0

Step 2: Open images as Layers into Photoshop CS5

Select all images of the sequence in Lightroom and choose Edit in > Open as Layers in Photoshop.

This opens all these images as a Layer Stack into Photoshop CS5

Step 3 + 4: Align and Crop

Run the StackAlignCrop script from File>Scripts. Warning: This script should only be used as described. This means if you just opened files from Lightroom or Bridge into layers you should not do anything extra to these layers prior to the calling the script. The script completely lacks any error handling in the case that you started with an ill-formed stack. As mentioned earlier you are entirely at your own risk using this script.

Note: As a welcome side effect: the alignment will likely be slightly improved over the normal CS5 auto alignment (the script uses an enhanced auto align version used by the CS5 "Merge to HDR" script).

Step 5: Export Layers into files

Fortunately Photoshop provides a script to Export Layers To Files. Destination: We use a temporary folder that we can synchronize with LightroomFile Name Prefix: We add a unique prefix so that we can keep the exported files in a clear sorting orderFile Type: - TIFF for lossless processing- Include ICC Profile for proper color management- I leave the TIFF options at their default. The bit depth depends on the original files. We use 16 bit.