The goal in creating an HDR image is to capture a wider range of lights and darks, than our cameras are ordinarily able to. The human eye can see a range of approximately 11-14 stops of light. But today’s cameras can only see about 5-7 stops. This means that we would look at a scene that has a lot of shadows and bright areas (like this one) and be able to see some detail in all of those areas. But when we try to make an image of that scene with our camera, we will likely get some areas with very dark shadows that are black where no detail can be seen and/or some bright areas that reigister as white, with no discernable detail.
In the HDR process, you capture mutliple (usually 3 to 5) images at varying exposures, so that some have detail in the dark areas and some have detail in the light. You then combine the images in your photo editing software, in a way that retains the dark area detail AND the bright area detail.
The above image is a pretty good example of this. Since it was taken as the sun was setting, there are many areas that already have deep shadows cast across them, and other areas where the sun is hitting directly, providing for very bright areas. To make this, I took three images, at -2EV, 0EV and +2EV, resulting respectively in one image that was black in the dark areas but had good detail in the bright areas, another that was exposed as the camera saw it, and a third that captured detail in the dark areas but not much in the bright areas.
I combined these in Corel Paint Shop Pro using it’s HDR Merge feature, made a few adjustments and there it is. We can see in this HDR image detail in the valleys which have already passed into deep shadows and the bluffs which are still facing the sun directly. I do think the bright areas on the nearest bluff are a little “hot” and would have liked it better if that area was not so bright.
HDR takes practice, both in capturing the individual images, and also in merging them. Many people have a tendancy to over-process the combined images, which results in some bizarre creations. If you are looking to create artwork or something abstract, then have a ball. But if you are trying to replicate the scene as your eyes saw it, then caution and restraint are advised. Rey is planning to author a post with an HDR tutorial, so stay tuned for more.
Posted by Ed