How to create HDR Photographs

For a while now I’ve been experimenting with creating HDR (High Dynamic Range) photographs and tonemapping them using Photomatix. The process of creating the HDR photograph and tonemapping it is relatively straight forward, but its not always easy to achieve a pleasing result – in fact its very easy to end up with a ruined final image of what was a perfectly good photograph to begin with.

This HDR tutorial will briefly explain the steps required to create an image such as this one shown below:

The above image was created from 7 exposures of the same scene, ranging from -4EV to +2EV, merged into a HDR image in Photoshop and then tonemapped in Photomatix.

Taking multiple exposures

The whole principle of creating a HDR photograph is to capture elements in a scene that you cannot get from a single exposure. Without going into too much detail, if you take a photograph and there are elements of it that are either too bright (overexposed) or too dark (underexposed), it is a candidate for HDR. By taking the same photograph at different exposure settings (or bracketing the shot), you can merge the resultant images into a single photograph called a HDR image.

The number of exposures you need to take may vary, I always shoot on the side of caution and take 7 bracketed shots, 1EV apart (mainly as my camera allows me to do this easily). I may disregard 2 or 3 of the shots as being too dark or too bright, but sometimes these shots have that little bit of extra detail I require.

Below are three of the exposures used to create the final image. As you can see, the photos range from very underexposed to quite overexposed. When I took the first normally exposed photograph, I could see that some of the details in the foreground were lost in the shadows, and the sky was overexposed. By taking 7 bracketed shots, I could get the full range of detail but no single photograph would have the desired final result. I could have opted for an ND Grad filter to stop the sky overexposing and allow me to shoot a couple of stops more to pull in that foreground detail, but with the light fading fast this wasn’t my preferred option.

The most important thing when shooting multiple exposures is that you keep the camera stationary and switch off the auto-focus after the first shot has been taken. Using a tripod to position the camera is the best method of ensuring no camera movement, although resting the camera on a wall or fixed object can work just as well. Removing the auto-focus will ensure all the photographs in the range will be identical in all aspects other than exposure. Personal preference is to set the camera with a medium aperture to ensure good sharpness and ensure a reasonable the depth of field is maintained – th elast thing you want with an HDR is too much bokeh (or blurred areas.)

Merging the photographs into a single HDR image

There are a number of options when it comes to merging the photographs into a single HDR image, including Photomatix (trail version), Artizen HDR (trial version), Qtpfsgui (free), and Photoshop (expensive). Personal preference again plays a part here, but all packages will do a reasonable job at creating a HDR image. All will attempt to remove ghosting, which is the problem of movement between exposures, often caused by trees blowing in the wind etc.

I like to use Photoshop for the merge stage, which in CS3 has an automate function to create the HDR image for you. Once you have pointed your choice of software to the correct files and it has merged, aligned, cropped and processed the files, you should have a single HDR image, that will look a little strange. The HDR photograph contains information (32-bit) that your monitor cannot display, so it requires further processing, such as tonemapping, to create a final image in either 8-bit or 16-bit format.

Tonemapping the HDR photograph

The next stage is to tonemap the HDR photograph. Again, the list of packages that will let you do this is extensive, including those listed above. For this part of the process, I prefer Photomatix.

When you open up the HDR image in Photomatix, you will see a button marked Tonemapping, this takes you to the relevant processing screen. I always start off with the defaults marked in the image below:

From here it is a case of playing with the sliders to get the result you want. I usually tweak light smoothing, luminosity, color saturation, strength and gamma to fit the result I’m after, but sometimes its simply a acase of try it and see what happens.

Single vs multiple exposure HDR images

It is possible to create a HDR image from a single RAW photograph, by adjusting the exposure settings of the image and saving them as separate photographs in something like Photoshop. While this technique can and does work, there is often debate over whether it can be considered a true HDR image. Personal opinion is that it is a form of pseudo HDR, and it can result in a final image that looks like a valid HDR and is pleasing to the eye. At this point it becomes a moot point in regard to its validity as genuine HDR image.

Having tried to create a HDR image from a single RAW file in the past, I’ve found that it much depends on the base file you are starting with – if it was correctly exposed in the first place, it is possible to obtain a reasonable final result after tonemapping, and its the tonemapping look and feel that you are really persuing if the image was correctly exposed in the first place.

If you want to try a single RAW file conversion to create a HDR iamge for tonemapping, Photomatix will allow you to do this via its single file conversion routine. I prefer however to take the RAW file and convert it first to 32-bit and then back to 8-bit in Photoshop, which forces you to then select the exposure setting. Do this three times (-2EV/0/+2EV) and you have your three different exposure files. You can then combine these back into a single HDR image. Single RAW file processing does have a benefit if you are trying to tonemap an image that has moving content – people/animals/vehicles etc, as you obviosuly don;t have to try and line up three or more separate exposures and remove the ghosting that occurs.

Like most thing in photography however, HDR and tonemapping does not save a poor photograph, regardless of whether its created from a single exposure or multiple exposures.

HDR and Tonemapping resources

There are a lot of resources on the web that go into much more detail on the steps outlined above. If you are interested in creating a HDR and tonemapped image, I suggest you read some of the following articles:

• Vanilladays – HDR Tutorial
• Cambridge in Colour – High Dynamic Range Photography
• Stuck In Customs – HDR Tutorial
• Realistic HDR photographs Tutorial
• Landscape HDR Tutorial
• PhotoshopSupport – HDR Tutorial

If you know of any other comprehensive HDR tutorials, drop me a line and I’ll add it to the list.

If you are attempting to create a HDR image for the first time, I recommend you practice and then practice some more. Find a scene that has highly contrasting areas of dark and light, and use it to develop your skills. Most of all enjoy the process of creating the final result.