Written on Nov 6th, 2008 by Dave Adams

Posted In: Photoshop

How To Create Stunning HDR Photographs

Aperture Priority, Balance, HDR, Photography, Photoshop, Shutter Release, Technique, Tripod

What is HDR Photography?

HDR stands for High Dynamic Range, and within photography refers to a process of combining multiple exposures of the same scene to enable the capture of both the darkest and lightest areas of a photograph.

While the human eye is very good at distinguishing between dark and light areas as it looks around, and adjusts the iris accordingly, camera sensors cannot adjust to compensate for an area in a scene that is both too bright (overexposed) and too dark (underexposed) all in one photograph.

To overcome this shortcoming, a system was devised where multiple exposures of the same scene could be combined into a single image, thus blanacing out any under or over exposed areas. With film photography, acheiving the same result would have meant doidging and burning a photograph to ensure an evenly exposed final image.

Once multiple exposures have been combined into a single HDR file, the image is then put through a tonemapping process, and it is this part of the process that most people think of when they talk about HDR photography. HDR photography has become so popular that it is no longer used to just compensate for over and under exposure issues, its actually used as an artistic technique to produce visually stunning digital artworks. In fact many of the HDR photographs that you will see on the web could have been taken with a single exposure with no tonemapping, as the dynamic range in the image is not that wide. however, the process of tonemapping can give a real lift to a photograph, and depending on the artist the effects can be anything from mild to wild.

The following HDR image is one I created from 9 exposures, tonemapped and then applied a Topaz filter to. I will talk a little bit about the best way of taking photographs for generating a HDR image, and give a little more detail on the way the following photograph was processed. It should give you some idea of whats possible with the software thats available today. I would put this in the medium-mild category - beyond photorealistic but not over the top.

Final Result after Tonemapping and Topaz Filter

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Creating Multiple (Bracketed) Exposures

So you like the look of the tonemapped HDR photograph, and you want to have a go at creating one your self. So what do you need?

The first item is of course your camera. Ideally it needs to be able to shoot in RAW to make the most out of this process. Shooting in JPG can work, but if your camera has a RAW mode, make use of it here. The extra information that the RAW fie holds will help in creating the HDR image, and increase the quality of the final photograph by reducing the amount of digital noise.

You also need to be able to control the exposure of the photograph. This can either be a manual process of adjusting the shutter speed or using a built in bracketing function. You should refer to your camera manual to see if your camera has an automatic bracketing option or not.

Bracketing means being able to take multiple photographs with differing exposures, producing a range of photographs that range from overexposed to underexposed. The middle exposure should be the roughly near the correct exposure for the photograph you are taking. If you cannot use an automatic bracketing function, you need to take muliple photographs of the same scene and adjust the shutter speed for each one, creating separate exposures that you can then merge into a HDR image.

The number of exposures you take can vary for creating a HDR image, you really need a minimum of 3 shots taken at -2, 0, and +2 to get enough dynamic range. You need to ensure that you take enough exposures far enough apart to cover the full range from light to dark of the scene you are shooting.

I prefer to shoot 9 exposures, and only use half of them, than only take 3 exposures and wish I’d got 7.

Below is one of the exposures from the bike shot, which you can see has some blown (white) highlights, where the detail has been lost. In contrast the areas that were actually quite dark or black on the normal exposure now have detail in them. i.e. the overexposure has brought out detail that would ordinarily have been lost in the shadows.

Overexposed Photograph

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And this is the other end of the scale, the underexposed photograph. in contrast to the overexposed photo with its blown highlights, this has most of the detail lost in the shadows, but has captured the lighter, whiter elements in much more detail.

As all the exposures are merged, there is a cancelling out effect that means those dark and light areas become balanced.

Underexposed Photograph

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Its important when you are shooting the multiple exposures that you keep the aperture constant and the camera completely still. To keep the camera from moving, I recommend you use a sturdy tripod and remote shutter release, as these will ensure minimum movement. If you try and take multiple exposures handheld, you will find that at the merging stage the images become blurred unless you have the perfect technique for holding the camera still while pressing the shutter button. While handheld shots can work, its better to increase your chance of success by using a tripod.

Merging Multiple Photographs

Right, you’ve managed to find something suitable to photograph, have setup your tripod and switched your camera to auto bracketing with fixed aperture and taken 3/5/7/9 shots using your remote shutter release. What next?

Well, you need to transfer those images across to your PC and then merge them into a HDR image. There are several ways to do this, my personal preference is to use Photoshop CS3 and use the Automate > Merge to HDR function. If you have used a tripod, your don’t even need to use the ‘align layers’ option. Simply select the expsoures to merge and let it do the hardwork.

However, if you haven’t got Photoshop CS3, or you neglected to make use of a tripod, you might need an alternative. Again, personal preference plays a part here, but Photomatix offer a trial version of their software, and it does a great job of merging exposures to create a HDR file. It even has some advanced options to try and line up images that are not quite aligned. Other options are Artizen HDR (trial version) and Qtpfsgui (free.)

Tonemapping the HDR file

Whichever mechanism you use to merge the exposures into a HDR file, you will then need to tonemap the image to make it look right. Again, there are various options when it comes to tonemapping an image, but I’ve had most success with Photomatix.

Once you have opened the HDR file in your package of choice, you can start playing around with various sliders and tabs to apply effects to the image. Some will give you that really over the top look, others will be much more subtle. The key one to look out for, at least in Photomatix, is the light smoothing option. The lower (more to the left) you choose, the more haloing you will see around the edge of any surfaces where colour contrast is high.

My approach here is to keep the light smoothing option to the right and keep the image looking more natural. The photograph below is the bike post-tonemapped in Photomatix. As you can see its reasonably subtle, and doesn’t have that pop that the first photograph in this post has. That comes in the next step.

After Initial Tonemapping in Photomatix

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Post-processing in Photoshop

So you have now applied some tonemapping, and you may have an image you are more than happy with. If thats the case, you can stop here and go and get yourself a well deserved drink. However, you may feel that there is further room for improvement.

If you open up the photograph in Photoshop (or whichever photo package you prefer to use,) you can start adjusting the level, curves and saturation to make sure that everything looks correct. You may even want to start using the dodge and burn tools to finalise any areas that have become over darkened or over lightend by the tonemapping process.

Further Processing with the Topaz Adjust Filter

The photograph I posted at the top of this article was further processed with the Topaz Adjust Filter which is available as a free trial version for Photoshop, should you wish to try it out.

The Topaz Adjust filter doesn’t require a HDR (tonemapped) image to start with, but I’ve found it gets by far the best results if you start off with a high quaility HDR file that has been lightly tonemapped before you use it.

Final Result Using The Topaz Filter

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