Love it or loathe it, HDR (high dynamic range) imaging is now a well-established digital photography technique, and one that looks set to stay. For those of you unfamiliar with the term and its implications on images, dynamic range in photography refers to luminance, or brightness, range. It can be used in reference to the luminance range in a given scene – from dark shadows to bright highlights – also known as the subject brightness range (SBR), or with reference to the luminance range of a camera’s sensor.
Your camera’s sensor is capable of capturing only a certain brightness range between shadows and highlights, usually measured in EV (exposure value) or f-stops. Outside this range, dark shadows underexpose (‘fill in’) and record as pure black, while at the other extreme bright highlights overexpose (‘blow out’) to detail-free white. The wider the sensor’s dynamic range, therefore, the more detail the camera is capable of recording in a high-contrasting scene.
Highlights or shadows?
Often the scene you’re photographing will exhibit a dynamic range within the sensor’s native capability, in which case (with the correct exposure) the camera is capable of recording both shadow and highlight details. But there will also be numerous occasions when the scene’s dynamic range exceeds that of the camera’s sensor. Think of a bright sunny day in shady conditions. In these instances the sensor is unlikely to be able to record detail in both highlight and shadow regions, and historically a photographer’s role was to decide which end of the dynamic range to record, shadows or highlights. In digital photography the rule of thumb was to expose for the highlights (to avoid them overexposing), as you might be able to retrieve some detail out of shadows, which certainly isn’t the case with blown highlights. With HDR imaging, however, we no longer have to make that choice. HDR allows us to create an image that contains the entire luminance range present in a high-contrasting scene.
The HDR technique can be separated into two main elements – capture and processing. In the first, capture, we use multiple exposures using incremental shutter speeds to capture the full brightness range present in the scene (see box Shooting for HDR). In the second, processing, HDR software merges together the various exposures to create a 32-bit HDR image. However, because our low dynamic range (LDR) monitors and photo-quality papers are unable to display the luminance range present in the 32-bit file, the image undergoes an additional process known as tone mapping. There are a variety of tone mapping methods, but the most successful use complex algorithms that adjust contrast locally by mapping tones and colors together. In this way different areas of an image can be adjusted to the optimum brightness, thereby compressing 32-bit luminance into 16 bits. It’s how well software can implement and control the tone mapping process that determines the look of the ‘HDR’ image, and that’s the purpose of this review.
Shooting for HDR
To capture the full range of tones present in a high-contrasting scene, the methodical way is to lock the camera to a tripod and use the camera’s spot meter mode to record the lightest and darkest elements of the scene. Select the Aperture priority mode (to ensure depth of field remains constant) and choose an appropriate aperture setting. Point the metering spot at the darkest part of the scene and record the shutter speed. Next point the spot at the lightest part of the scene and again record the shutter speed. Let’s assume the first reading of the darkest shadow presented you with a shutter speed of 1/4 sec, and the second reading of the highlights 1/125 sec. In this instance the dynamic range is 6 stops. Therefore to record the entire range of tones you would need to shoot 6 frames with a 1EV gap or 3 frames with a 2EV interval. With a 6-stop range you can use the camera’s auto-exposure bracketing (AEB) to shoot the sequence. Most DSLRs allow you to shoot three (or even more) bracketed shots of between 1–2EV stops. Using bracketing in tandem with the continuous shooting mode will result in better alignment as the images are taken quickly in succession without you having to touch the camera to adjust the settings. And in fact, the alignment features of many HDR software are so good now that you can often shoot a bracketed sequence handheld and still obtain good results. If the dynamic range or SBR exceeds the range that the camera is capable of capturing using the bracketing feature, you’ll have to adjust the shutter speed manually.
Finally, we recommend that you shoot in the Raw file mode as this will provide the most image data when you come to create the HDR file. In addition, with HDR programs that exist as plug-ins for Lightroom or Aperture, you can pre-process the Raw files – fixing issues such as chromatic aberration, noise, dust and so on – before exporting the files to the HDR software and creating the 32-bit HDR file.
As the metered shot and accompanying histogram show, the dynamic range of this scene, thanks to the combination of bright sky and dark shadows, exceeds that of the camera’s sensor. Using three bracketed exposures of -2EV, OEV, and +2EV covers the scene’s dynamic range, and the images can be combined together using HDR software to create a single HDR image.
The three main factors that we concentrated during the course of this test were speed, ease of use, and results.
Photoshop’s first HDR feature, Merge to HDR…, was introduced with Photoshop CS2. Subsequent versions of Photoshop made little improvement to this original HDR tool, which was generally thought of as unwieldy and lacking control. However, with CS5 things have improved. Photoshop’s HDR command is now quicker and offers greater levels of control.
Once you’ve selected your bracketed sequence and exported to Merge to HDR Pro… (via File > Automate, Bridge, Mini Bridge, or even through Lightroom) Photoshop immediately sets to work importing the selected files into layers and creating the 32-bit HDR file. Although not the quickest on test, the new ‘Pro’ version of Merge to HDR… is certainly faster than its predecessors. Times of course will vary depending on your specific computer and the number and size of the images in the bracketed sequence.
The Merge to HDR Pro… workspace is clear and uncluttered. The main preview sits adjacent (either above or to one side depending on the format of the main image) to thumbnails showing the bracketed sequence, while the main control panel is found on the right-hand side.
By default the 32-bit HDR image is converted into a 16-bit tone mapped image ready for processing. You can choose to process the image as an 8-bit file, but you’ll be losing a great deal of information and the image is likely to suffer as a consequence as you process it.
Tone mapping methods
Although Photoshop offers four tone mapping methods, in reality Local Adaptation is the only one you’re likely to use as the other three offer little or no control. Local Adaptation, on the other hand, offers a good level manual adjustment in the form of nine sliders grouped into three main sections, Edge Glow, Tone and Detail, and Color. There’s also a Curve dialog should you want to adjust specific tones.
As well as the adjustment sliders, Merge to HDR Pro… also features a number of presets and a ‘Remove ghosts’ button. ‘Ghosts’ appear in HDR images due to moving elements appearing in different places relatively across the bracketed sequence. This could be a person walking down the road, or, as shown here, a flag fluttering in the breeze. When the Remove ghosts button is selected, Photoshop identifies the moving object and automatically assigns an individual frame to use in order to remove the ghosting effect. On all the images we tried the feature worked faultlessly, and it’s a real plus point of Photoshop’s HDR software.
Photoshop’s deghosting command uses one frame from a bracketed sequence to avoid moving objects from the multiple exposures appearing in slightly varying places. Photoshop’s feature works extremely well, and simply clicking the Remove ghosts box will usually automatically resolve any ghosting issues.
Less effective are the presets styles. These range from a variety of monochromatic options (why so many is a bit of a puzzle), through photorealistic to surrealistic. None will give you the finished article straightaway, but that’s not to be expected, however nor do they really inspire confidence to use them as a starting point. You can however, as you can with all the programs here, save your own custom settings as a preset, and that’s probably the way to go with Photoshop.
Although it’s possible to tease out photorealistic and hyper-realistic images using Photoshop’s HDR tools, the process involves a certain amount of trial and error and a good understanding of tone curves. Once you’ve got a punchy, nicely contrasting image using the Curves dialog, it’s a case of playing around with the Detail, Radius and Strength sliders (these three determine the main tone mapping effect) until you arrive at the result you want.
The results on the various sequences we tested all seemed to point to the same conclusion. Photoshop’s Merge to HDR Pro… feature is capable of producing attractive, photorealistic tone mapped images, but less able to come up with the more surreal images that many users will be after. In many cases increasing the Detail slider led to halos that were difficult to alleviate with the Radius and Strength controls. It was easy to achieve a very contrasting or soft surreal result, but emphasizing texture and detail without introducing halo artefacts was often difficult to achieve.
Attempting to make the most of the texture and detail in this image using Photoshop’s HDR tools involved a certain amount of trial and error, and the image needed extensive sharpening in Photoshop following the tone mapping process. However, the final result is a pleasing photorealistic image, which tends to be Photoshop’s strongest card.
Images are natural looking
Difficult to control
Launched in February 2003, HDRSoft’s Photomatix was the first HDR software widely available and has won many plaudits over the years. Now in it’s fourth version, Photomatix Pro has evolved with the times and is still the best-selling HDR software.
Available either as a standalone program or a Lightroom plug-in (cut down plug-ins are available for Aperture and Photoshop), Photomatix begins the tone mapping process via File > Load Bracketed Photos… or in Lightroom by right-clicking the highlighted sequence and selecting Export > Photomatix Pro. Alternatively you can simply drag the bracketed sequence onto the Photomatix desktop icon.
Before the processing begins, you’re presented with a ‘preprocessing’ dialog box with a variety of options. The options vary slightly depending on whether you’re exporting TIFFs from a Raw editor or opening Raw files directly in Photomatix. In either case, most of the options are self-explanatory. You’ll need to experiment with the noise reduction options, but we found reducing noise on normal and underexposed images provided the best results.
As a Lightroom plug-in Photomatix’s preprocessing dialog offers useful options. If you’re intending to undertake further post-production work on the tone mapped image set Output Format to 16-bit TIFF. This will ensure the tone mapped image retains as much data as possible for you to work with.
Photomatix ghost removal
Photomatix’s deghosting feature can be set to work automatically or semiautomatically. The semiautomatic option is the recommended method and with our tests it worked as well as Photoshop’s deghosting features.
In Photomatix Pro’s semiautomatic deghosting routine, you manually select the area you want to deghost in a preview screen and, as with Photoshop, Photomatix then automatically selects the ‘master’ frame. If you’re not happy with the preview result, you can change the frame Photomatix uses.
Having made the preprocessing selections, click Export for the tone mapping process to begin. If you have checked the semiautomatic deghost routine you’ll be presented with the preview window described as shown before the processed image appears. All in all, Photomatix works at a comparable speed with Photoshop.
Photomatix’s workspace may at first appear a little more daunting than Photoshop’s. It comprises three main elements – a large image preview, the tool panel, and a filmstrip depicting thumbnails of Photomatix’s various presets.
Photomatix has two processes with which to combine your images, Tone Mapping and Exposure Fusion. Exposure Fusion does not utilize tone mapping algorithms, instead it compares the luminosity, saturation and contrast of the bracketed sequence and automatically combines, or ‘fuses’, the images together taking the accurately exposed elements from the bracketed sequence to create a single optimum exposure. It’s something you can do manually in Photoshop using Layers, but Exposure Fusion does it automatically, and then allows for some manual adjustment. The benefits of Exposure Fusion are that the final image is less likely to suffer from noise, halos and other artefacts that can often affect a tone mapped image. However, Exposure Fusion cannot create the surreal, painterly effect that many seek with the tone mapping process. But if it’s a natural-looking result you want, then Exposure Fusion is certainly worth trying.
Photomatix has two tone mapping methods, Tone Compressor and Details Enhancer. Tone Compressor is a ‘global’ tone mapping operator (as opposed to a ‘local’ operator) and is capable of producing pleasingly balanced images, but with fewer localized adjustment controls to tailor the look of the final image.
Details Enhancer is the default tone mapping option, and the one that offers the greatest level of control and tone mapping variation.
One of the most striking differences between Photomatix and Photoshop is the preset options. Photomatix’s presets (which include Exposure Fusion and Tone Compressor options as well as Details Enhancer presets) are much more viable than Photoshop’s, often requiring only minor adjustment before you reach a satisfactory result. If not, then Details Enhancer has 15 sliders to help you get the result you want.
The five principal controls are found at the top of the tool panel, with the 10 additional sliders presented as ‘More Options’ and ‘Advanced Options’, which can be revealed and hidden using the relevant disclosure triangle. The key ones in terms of controlling the tone mapping process are Strength, Detail Contrast, and Lighting Adjustments. We found these worked more intuitively compared with Photoshop’s principal tone mapping controls. Among the additional optional controls, of note are Smooth Highlights and Micro-smoothing, which help to keep skies noise free and reduce halos respectively, two common problems with tone mapping.
Photomatix is a highly versatile HDR program. It’s capable of generating both photo-realistic and hyper-realistic styles of imagery relatively quickly thanks to the workable presets and the excellent level of adjustment control.
On the whole Photomatix Pro feels much more intuitive than Photoshop’s Merge to HDR Pro… feature, and thanks to the presets inspires experimentation. Photomatix is capable of producing a wider variety of styles in a shorter space of time.
In our experience what Photomatix really excels at is creating a soft painterly atmosphere to images, which works particularly well with landscapes.
Versatility of tone mapping methods
Good level of control
Experienced users might miss a tone curve control
HDR Efex Pro
From the most established to one of the more recent HDR programs, HDR Efex Pro was launched in late 2010. It was developed by the respected digital imaging software company Nik, and as a dedicated HDR program is in direct competition with Photomatix Pro.
HDR Efex Pro is available as a full plug-in for Photoshop (via Bridge), Lightroom and Aperture, and although it can be used as a standalone program, it runs less efficiently that way.
As a plug-in, select your bracketed sequence from whichever program you’re using and export to or open with HDR Efex Pro. In our tests we found the HDR Efex Pro was the quickest to present the tone map preview, although unlike Photomatix is doesn’t run any noise reduction algorithms to slow things down.
The first opportunity you have to address any ghosting issues is when you’re presented with the processed preview. Again this speeds up the workflow, and if you do have ghosting to resolve you can click the Alignment and Ghost Reduction tab at the top of the screen. These settings can also be accessed via the Settings panel, where you’ll also find other setting options such as output format and re-import options.
HDR Efex Pro performed less well than either Photoshop or Photomatix with its deghosting routine. Despite trying all the various options in the Ghost Reduction dialog, as the close up image shows, there is evidence of ghosting around the Union flag. How much of an issue this for you, depends on the type of HDR photography you do. Clearly if you shoot outside where people and cars are moving and trees are swaying then you’ll need to consider how much of a problem this is. If you shoot still-life then there’s clearly not an issue.
HDR Efex Pro’s workspace is attractive and feature rich. On the left-hand side of the large preview (which can be set to show before and after views) is a row of preset thumbnails, while on the right is the main control panel. All in all the entire experience is reminiscent of working in Lightroom, Capture One, or Aperture, making photographers feel quite at home.
The 33 presets (far more numerous than Photomatix) are organized into categories – although these shouldn’t be rigidly adhered to as you may find a preset in the Landscape category that works very well for an architectural shot and vice versa. We found it easiest to have all the presets available to view. There’s a huge style of presets, ranging from the realistic to the surrealistic, and although you’re unlikely to use some, they are sufficiently well-rendered to use as starting points.
There’s no doubting that HDR Efex Pro offers an extraordinarily high level of control, including Nik’s powerful ‘U Point’ localized adjustment feature. However, despite the myriad of controls on offer, the sliders are quickly learned and behave logically. An excellent feature of the software is that adjustments are made in real time – the image updates as you move the slider and this really helps speed workflow.
One of the features that Nik Software has incorporated in much of its imaging software is ‘U Point’ technology, and HDR Efex Pro is no exception. For those of you unfamiliar with U Point, it’s a powerful means of applying localized adjustments to contrast, brightness, colour saturation, and so on, to any part of the image. This in effect ensures that you can perform just about all the editing to the processed image in HDR Efex, rather than relying on Photoshop, Lightroom or Aperture to complete the job.
As well as the powerful U Point command, other features that reinforce Efex Pro as a one-stop shop are the Finishing Adjustments tools. These include Vignette options and a Levels and Curves dialog, where you can tweak the image’s local brightness and contrast before saving.
Like Photomatix, HDR Efex Pro is a versatile HDR tool that really inspires creativity and experimentation, while at the same time, thanks to its extensive tool set, can be used to create naturalistic imagery.
Out of the three programs on test HDR Efex is the best at highlighting texture. It has a ‘Structure’ setting that increases contrast at an extremely small scale. Its many and varied presets, despite obscure names such as Granny’s Attic, encourage users to experiment in ways they may not naturally have gone.
Of the three programs on test here, Nik’s HDR program was the most fun in terms of its creative possibilities. The presets provide some good and extremely varied options, although how many you’d use in the real world is debatable. That said, like Photomatix, HDR Efex Pro can turn it’s hand to pretty much any style of HDR imaging – naturalistic, hyperrealistic, to downright weird.
Powerful adjustment controls
So, which is the best? Much of that of course depends on your preferred HDR look. If you’re not after surreal, and simply want to create natural-looking, high dynamic range images, and you have Photoshop, then look no further – you have everything you need there, and with time and patience even Photoshop can produce a successful hyper-real image. If, however, you’re looking to be a little more creative, then you need to turn to either Photomatix or HDR Efex Pro. They’re both well-equipped, versatile programs that are capable of producing just about every imaginable HDR style. Photomatix’s algorithms tend to produce a slightly softer, more ethereal result that suits certain types of photography, whereas HDR Efex Pro, with its numerous presets, encourages you to think more creatively.
Both Photomatix and HDR Efex Pro are available as trial downloads. Have fun testing them!