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HDR from a Single Photo


Though not to everyone's taste, HDR (High Dynamic Range) photography can be great fun. I give a simple explanation of HDR in another guide which can be found here, and so I will not go over it again, suffice it to say, an HDR image usually requires three or more photographs of varying exposure to create the finished result. The following describes how to achieve a similar effect by using a single photograph. This can be very useful when it's just not practical to take 3 separate (positionally identical) pictures when you're out and about. For instance, you need to keep the camera very still and you may not have a tripod or a convenient surface to use as a support, or the subject may be moving. On this latter point, the following method is excellent for capturing large crowds of moving people, where otherwise three separate images from a camera would end up blurred





The image above was produced from just one photograph and illustrates the effect well, with detail in the shadows leaping out. But as with conventional HDR, not every subject is suitable. It's worth experimenting to find out what works and what doesn't. Generally, I've found that scenes with high contrast and lots of detail give good results



A normally exposed photograph before processing


The 3 or more separate images required for HDR would normally be captured by the camera at the time the picture was taken, but with only a single image to play with, the extra photos have to be created using a photo editor. Which actually isn't too hard to do. We all have our favourite photo editors and mine is a free program called PhotoFiltre. The feature that is going to be used is 'Gamma Correction' and any decent editor should have this

So first of all open up the photo that you want to process. A normal JPEG is fine but should of course be a correctly exposed good quality and preferably noise free image. Next, select the gamma adjustment and lower its value to about 0.6 as a rough starting point. The image should now appear darker. Save the image 'As' and name it 'LO'. Now go back to the correctly exposed image but this time adjust its gamma level to about 1.8. The image should now appear brighter. Again, save it 'As', but name it 'HI'. These names are just so you can differentiate between them easily later on. In practice, the gamma values chosen will vary depending on the photograph used, but with experience, you will get to know what levels work best. You should now have three photographs the same except for their gamma levels, and three are sufficient for this to work


                
                     Image with reduced gamma                            Normal image                            Image with increased gamma


The image processing software used is called Photomatix. There is a 'Pro' and an 'Essentials' version. I use the cut down Essentials version which works very well. A free trial can be downloaded here. It's fully featured but puts a watermark on the finished image which won't happen if you decide to purchase a license





The three images are loaded into Photomatix and clicking the 'Next' button will start the process off. I won't describe how to use Photomatix here as it's covered on their website (see link at bottom of page) but it's really straight forward. The software will combine the three pictures into one high dynamic range image which can be in JPG or TIF format. TIF is best as it can be edited later without loss of quality. On the subject of editing, it's worth spending a bit of time adjusting the colour and contrast levels to bring the image to life





The photo above is the result. As said earlier, not all photos work, but when they do, they can be quite amazing. Click here to enlarge

Links:
Photomatix Video Tutorial
Photomatix User Gallery
stuckincustoms.com