HDR effect created on single photo to correct dark areas and increase range

What is HDR?
High dynamic range (HDR) imaging allows a greater dynamic range between the lightest and darkest areas of an photograph than what standard digital imaging techniques or photographic methods. The wide dynamic range allows HDR images to more accurately represent the range of intensity levels found in real scenes, ranging from direct sunlight to faint starlight. This is generaly captured by way of differently exposed photographs of the same subject in the same setting.

Photo editing professionals are familiar with the issues of low dynamic range. If you brighten an image, some information is lost irretrievably. And then darkening the image after brightening does not restore the original appearance. Instead, all of the highlights appear flat and washed out.

HDR photographs are generally achieved by capturing multiple photographs, using exposure bracketing, and then merging them into an HDR image. But the above 'before and after' is an example of HDR simulation done right on a single photograph using advanced photo editing skills.