High Dynamic Range Photography

More Information About HDR

Before any post processing can occur, the image must be "tone mapped" so that resulting HDR image is viewable and editable. If you recall, tone mapping is the HDR software's way to "compress" the dynamic range to a range that can be displayed using today's media/monitors. So basically the brightest parts of an image are darkened, while the darker areas are lightened up providing more detail in both of these areas and bringing the dynamic range to a more central range.

As you might have guessed, this can create some undesirable effects with your images, such as a flat looking or low contrast images. I have also noted that many HDR images can have a gray (or color) cast that is introduced when the tone mapping is completed. Sometimes it is difficult to see the color cast when the images are generated, but once you do a few of these tweaks I think it will be much more apparent, and the corrective actions are not too difficult. The effect sometimes can look like you are wearing colored sunglasses when viewing the image and they have an unnatural look to them.

My workflow follows like this: I bring the tone mapped image into my photo editor which happens to be Photoshop, but you can do similar changes using Elements or one of the other photo editing packages. First I make myself a copy of the image on a new layer, I do this so I always have the original image to fall back to in case I want to refer to or go back to it (non-destructive editing). Next I will generally do my sharpening at this point, again depending on your editor and the amount of sharpening is dependent on the image.

The key to sharpening to me is not to overdo it. Too much sharpening can cause the image to look hard and unrealistic.
Once the sharpening is complete I will then do a black/white point levels adjustment. In Photoshop there is a tool that lets you use an eyedropper to select the blackest area on your image and one for the whitest area and this will bring the image to a more realistic look.

So for instance an image that has clouds in it you can use the white level selection to pick out the brightest part of the cloud and then with the black level eyedropper you select an area that is dark and this will transform the image as seen in the images above showing the color cast removed. Now sometimes you don't have a pure white area in which to select from and or a black shaded place, in these cases you can use the manual level adjustments to bring some contrast back in and help remove any color casts. I have generated a small video showing me doing this which will help get idea across. Click directly on the image below to play this movie here, within the PDF file.

So, we have done some sharpening and color cast correction, lastly I normally will run some noise reduction. After tone mapping you will typically notice more noise in your images especially in the shadowed and sky areas. Run your noise reduction to help make your final images noise free. If you don't already have a noise reduction program there are several great ones out there, Neat Image and Noise Ninja to name a couple or if you have Photoshop it even has a noise reduction filter built in.

Daniel Kreimer