Scott Kroeker wrote:
I always use a filter over HDR if possible.
To clarify, exposure blending is not necessarily HDR. What we normally think of as HDR accomplishes a very different thing - a sort of local contrast enhancement throughout the frame - while exposure blending is closer to using GND filters in concept and result. It also tends to be a lot more labor-intensive since the blending work is typically done manually by \"painting\" on layer masks.
A quick review. The basic idea of the exposure blending approach goes something like this...
Given a very wide dynamic range subject, the photographer decides to make two (or more) exposures of the scene, usually but not quite always from the tripod. Using a two-exposure model for my explanation, one exposure is optimized for shadow details (and probably results in blown out highlights) while the second is optimized for highlight details (and probably results in blocked shadows).
In post the two images are layered one on top of the other - for my example I\'ll assume that the highlight-optimized image (e.g. - the one with blocked shadows) is on top, though there are certainly situations in which they might be reversed. A layer mask is added to the upper layer. (You could use \"hide all\" or \"show all\" depending on your goal. I\'ll assume that your mask shows the upper layer and hides the lower one.) Using a soft-edged brush tool and a relatively low opacity, the photographer \"paints\" on the layer mask to reveal the better shadow detail areas of the lower image. (A simpler method that almost literally reproduces the effect of the GND is to select the darker area and simply create the mask for it all at once.)
While this method can do exactly what the GND method can do when used in its most basic way, it can also offer some very useful options that are either not available or only available with some very tricky techniques using the GND filters. Some of them include:
- The difference between the dark/light areas can be however many stops you want it to be rather than being limited to the difference between the clear and filtered areas of your GND. If you want a 5 stop difference or a half-stop difference, you simply expose \"perfectly\" for your bright/dark areas in that way.
- The exposure blending method allows boundaries between the light/dark areas that are not straight lines. A favorite example of mine involves shooting out of the entrance of a steep and narrow desert canyon into the open desert beyond. The v-shaped canyon walls were in deep shadow, but I wanted to retain some detail in this dark area. However, the correct exposure for these shadows resulted in a badly blown out desert in the distance. I was able to exposure blend in a v-shape, which would have been next to impossible with filters.
- The photographer can \"spot blend\" various areas of the scene. For example, it a photograph with mixed sun/shade areas (the infamous \"pizza light\") it is possible to bring a bit of detail back into shadows throughout the scene using exposure blending.
- In my view, exposure blending can do a more effective job than HDR (at least if the HDR isn\'t used with a great deal of care and subtlety) of creating a photograph that works the way we see. When our eyes move around a scene our pupils tend to adjust to the brightness of the area of the scene that we look at. This is one reason why you can \"see\" into the shadows on a very bright day, then lift your eyes to the bright clouds and not have them appear to be blown out. In essence, blending allows the photographer to simulate something analogous to this in the print.
There are some challenges to using blending. Obviously, you need to make more than one exposure. This (almost) necessitates the use of a tripod and it can take a bit of extra time - though once you learn the technique the process is very quick and a lot quicker, I think, than using the filters. There can be issues with elements of the scene that move, though in actual practice this turns out to be much, much less of an issue than you might imagine. And, just as with the filters, some skill is required in order to create blends that don\'t reveal the technique itself.
I\'ll close with a photograph created using the blending technique - and one that would have been very difficult, if not impossible, to produce using filters as the dynamic range of the scene was huge. The image is a blend of three photographs.
(By the way, I never use HDR. I\'ve tried it a few times but not been happy with the result of felt that it was really necessary. However, some photographers that I respect a great deal tell me that they do use HDR in some very subtle and powerful ways. I still need to look into that more carefully.)
Dan
Jun 25, 2012 at 10:51 AM
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