When most people think of HDR, they think of grungy, over-saturated photos with “halos” around objects with edges (trees, buildings, etc). In reality, that isn’t HDR – that is just a method of tone mapping.
What is HDR?
HDR stands for High Dynamic Range, and that simply means that the photo had more dynamic range than the camera could capture in one single shot. In order to create (not take) a photo that has high dynamic range, you generally will take 3 or more photos, and one of them will be your properly exposed base photos, with at least a couple being overexposed and underexposed – these capture the details in the highlights and the shadows. A HDR file is usually created as either a 16-bit or 32-bit image.
Understanding The Scene
Cameras come from the factory with sensors that can record a scene with a specific dynamic range. For the old Nikon D70, that was 10 stops. For the Nikon D600, it is 14 stops. With a lot of cameras, you have to also figure that about 3 stops on the lower and upper ends of the scale have a little noise inherently to them. The effective range of the D70 was usually around 6-8 stops, depending on the scene. If I was shooting a scene that didn’t have a lot of dynamic range, I didn’t need to shoot brackets, but if I was shooting a scene with sky, clouds, and a dark car, I certainly needed more dynamic range, so I would shoot brackets of +2 EV and -2 EV, along with the base exposure, and combine them to create an HDR photo.
In order to create a HDR photo, you then need to combine all of the exposures into one photo. One easy way is with Photoshop, as it has it already including in the latest versions. The program knows what to select from each photo, and how to process them. Depending on the version that you have of CS, you can select to let it make either a 16-bit or 32-bit file. Obviously, a 32-bit file is quite large, but gives you the most flexibility when you are ready to edit.
At this point, you have an HDR photo and you will notice that it is not grungy or very saturated. It does have a high dynamic range though, as it includes the values from all three photos into the one photos. The HDR part is actually complete at this point, and is ready to be processed and created into the look that you want.
The photos that the HDR program creates are generally flat, and of low contrast. This is where tone mapping comes in.
What Is Tone Mapping?
To really simplify things, it is nothing more than adjusting the colors in the photo to what you want. When you hear this term used in conjunction with HDR, it generally means over-saturated, high contrast, etc. – but it doesn’t have to be.
I like to export my bracketed photos from Lightroom into Photoshop and let the PS HDR program combine them, then import the combined file back into Lightroom, and then process it normally. This allows me to generate a photo with high dynamic range, which gets all of the details (without the noise), and keeps it natural looking.
If I want the over-saturated “HDR look” that you see so much of today, I use Photomatix Pro, as it seems to give me the best results for that look.
In reality, you don’t have to have a bracket set of photos to tone map. You can use a single image in NIK’s HDR EFX, or in Photomatix, and create a tone mapped image. This is why tone mapping and HDR are not the same thing – each has it’s own place and process.
It’s All About …
Style. Ultimately, you have to chose what methods you want to use to present the image to the user in the way that you like. That might be realistic, or surrealistic. Either way, an HDR image simply has more dynamic range than your camera could get in one exposure, and the way that you process the combined images controls the look of the photo.