Exposure Bracketing to Create High Dynamic Range (HDR) Images
April 24, 2018 • Leave a Comment
Exposure Bracketing is a process used to capture images with a high dynamic range hence the commonly used term HDR.
When would I use Exposure Bracketing?
Typically exposure bracketing is required when the scene that we wish to photograph has more tonal range than the camera can capture in just one exposure, for e.g. a wedding where the bride wears white and the groom wears black. This isn't as clear cut as it sounds because it takes some skill and experience to know when this is required. However, it is true that some people use HDR to create a certain look and may use this process even if the camera can capture the full range of tones in a scene.
How Do I Take Images using Exposure Bracketing?
Many cameras have the facility to take exposure bracketed images as a built in feature, some cameras even have an automatic HDR mode. Many consumer DSLR's will allow you take three bracketed shots out of the box whereas many higher end cameras will allow 7 or even 9 bracketed shots. These by themselves are NOT HDR images but are just several shots of the same scene taken over an range of exposures. However, there are cameras such as the Canon 5D Mk3 which also have an additional HDR mode which will produce a number of bracketed shots and a processed HDR image from those shots, all done by the camera.
Some cameras do not have a exposure bracketing mode but, all is not lost because exposure bracketing can be done manually. All that is required is to setup your camera on a tripod, set it up to shoot the scene in manual mode and adjust the exposures to capture several shots from underexposed to over exposed.
Why Bracketing and Why Have Under and Over exposed Images?
In photography, bracketing is the general technique of taking several shots of the same subject using different camera settings. With the standard 3 shot exposure bracketing the camera will take one image on the correct exposure, one image under exposed and a third image over exposed.
What is the reason for the different exposures I hear you ask? Well, if you think about the scene you wish to capture which we know has a wide tonal range from blacks in the shadows to whites in the sky. The camera cannot capture this full range of tones so the camera will either exposes for the highlights and makes the shadows black (underexpose) or it will expose for the shadows and blow out (overexpose) the highlights or it can meet somewhere in the middle and get the mid-tones right but make a poor attempt at both highlights and shadows.
So instead of any of these we take three shots, one for the highlights, one for the shadows and one for the mid-tones. We then use a clever piece of software and blend all three of these images together and create an image which uses the best tones from each shot to create the HDR image.
Why You Should be Careful Processing HDR?
It is a fact that the majority of photographers have used the 'Grunge' pre-set effect that is available in some software such as Photomatix to create weird high tone and high contrast images like the one below. I suppose it is a phase that we all go through and ideally move on from after reality hits and we realise that the images are not that appealing to most viewers.
The key to a successfully processed HDR image is when the viewer cannot tell that it has been processed yet the image has good tones throughout the entire tonal range.
Can I Spot an HDR Image From a Normal One?
The tell tale sign of an HDR processed image is usually very dark edges to clouds and the image above is no exception to this. However, in its case it is pretty obvious that the entire image has been given the 'Grunge' type treatment. The image below which has little visible HDR processing but again the clouds are a dead give away.
The best HDR processed image is the one that can't be distinguished from a normal single exposure. The blending of images is carefully controlled so only the areas that need the tones are affected etc. The image below is also a 7 shot HDR but is has been much more carefully processed and is stark contrast to the first image which is way over the top.
So What Software Should I Use?
There are several software programs for processing bracketed images which will create HDR output. Photomatix is a popular choice and one that I have used many times. There is also the popular Photoshop plug-in within NIK Software (Google) suite called Merge to HDR efex Pro and there's also good old Photoshop which has had a merge to HDR tool since CS2.
However, with the advent of CS6 CC there is a new method of processing HDR images and this is the method that I now use. With Adobe Camera RAW version 7.1 or later comes the ability to edit 32bit TIFF images directly in Camera RAW, a feature not yet available in Lightroom as Lightroom cannot yet process 32 bit images.
Using the Photoshop tool, the process is fundamentally this. Highlight your bracketed images within Bridge and in the 'Tools' menu select 'Merge to HDR'. This processes the images as layers into Photoshop and creates a HDR image which you can then save as a 32 bit TIFF file. You then have the ability to open the image into Camera RAW and process it yourself rather than having to rely on a predetermined style as in the other programs. Also with the advent of the Camera RAW filter in Photoshop you can work on the image entirely in Photoshop.
***NOTE*** Please take note that processing images in this way can lead to some very large image files, the more bracketed shots that you use the bigger the file. For e.g. the original of the third image in this post is a 7 x 25MB bracketed HDR file. The size of the originally processed HDR TIFF file is 264MB, the JPEG created from that TIFF file is 38MB.
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