So far, we talked about mixing different spectrums or different images. A relatively new technique that involves mixing different versions of the same scene is High Dynamic Range photography. In this technique, we mix multiple shots of the same scene, taken at different Exposure Values (EV). EV, in camera settings, denotes a combination of exposure time and relative aperture. Rules and suggestions about the optimal EV settings for different subjects are extensively covered in the theoretical books and websites about photography and are not really within the scope of this book.
What is within the scope of this book, is to understand what the mixture of multiple EV pictures can accomplish. In a nutshell, it makes the resulting photograph have a greater dynamic range between dark and bright areas in the image. However, to use this technique to its full power, the images that will be mixed should not be 8-bit, since the range of 256 values per color contained in them normally produces artefacts.
Since the average reader of this book normally has access to 8-bit images, we will use such an example for our demonstration of the method. But first, we will say a word or two about how to shoot the required images.
First off, you should have a camera that supports manual settings. Second, you should find the setting for Auto Bracketing, which will allow you to shoot with multiple exposures. Some cameras give you a choice of three different EV values (usually -2, 0, 2, or -1, 0, 1), while others have more stops available. An alternative is to manually adjust your preferred ISO and f-setting and then, using a steady tripod (and ideally a remote control, so that you do not move your camera at all) to shoot with at least three different exposures. Immobility is of the essence, since moving the camera or shooting mobile subjects will result in blurred areas.
After you have taken your three shots, you will have to use the MATLAB's makehdr function to compose the HDR image and then use tonemap to render the resulting image for viewing purposes. Let's see an example that demonstrates all these.