High Dinamic Range images or HDR, is a set of methods used in imaging and photography to allow a greater dynamic range between the lightest and darkest areas of an image than current standard digital imaging methods or photographic methods.For obtaining such an image the photographer will take multiple pictures at different exposure levels and intelligently stitching them together to produce a picture that is representative in both dark and bright areas.
Results after processing
Local tone mapping
For processing the images software are used like Adobe Photoshop or Photomatix, that allows you to edit the images and stitch them together.The important part of creating the final image is the Tone Mapping, using for example Photonatix you will have control over multiple settings like:
Luminosity- Adjusts the brightness of the shadows.
Strength- Controls the strength of local contrast enhancements.
Color Saturation- Controls the saturation of the RGB color channels.
White Clip – Black Clip- From watching the way the histogram changes, the white clip adjusts the highlight contrast and the black clip adjusts the shadow contrast.
Microcontrast- Controls the accentuation of local details.
And other settings that allows you to achieve the result that you want.Shooting the images on high ISO is not recommended even if you shoot on ISO 100 the image is going to be a little noise, but if the images are taken with higher ISO the result will be with a lot of noise. A great more detailed examples are found here : HDR Tutorial