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In this course, photographer Ben Long describes the concepts and techniques behind high dynamic range (HDR) photography, a technique used to create images that have a wider range between the lightest and darkest areas of a scene than a digital camera can typically capture. The course begins with some background on dynamic range, on how camera sensors detect shadows, and on the kinds of subjects that benefit from HDR. Ben then describes and demonstrates several methods of generating HDR images, starting with single-shot HDR, which relies on masking to subtly enhance the dynamic range of a shot. Next, the course covers multi-exposure HDR, which involves shooting several photos of a scene, each at a different exposure, and then combining them using software tools. Ben demonstrates how to use Photoshop and the popular Photomatix software to process HDR images whose appearance ranges from subtle to surreal.
In our earlier walk-through of Photomatix you saw that there are two different processes to choose from: Tone Mapping and Exposure Fusion. We looked at Tone Mapping in detail. Now let's take a look at Exposure Fusion. Switching over and the first thing that happens is, as I mentioned before, my image becomes a little less HDR and starts to look a little more like a normal photograph. That is my shadows are not so perfectly exposed, my highlights aren't so perfectly exposed. It doesn't have that flat look that an initial HDR adjustment can have. I also don't have the super refined detail.
So if you want to be able to have good exposure throughout your image, that is, have some detail down here and have some detail up here, without going to the full HDR look, Exposure Fusion might be a good option for you. As I mentioned before, this is basically blending my stack of images together in the same way that I might do in Photoshop using a bunch of layers. Within Exposure Fusion I have five different methods to choose from. The default is going to be Fusion-Adjust, and it's not a bad place to start.
I've got all these different controls. Let's just take a quick look at them. Accentuation, as I drag it to the right, is going to make local contrast adjustments a little bit stronger and as with some of the sliders in the Tone Mapping, what that's going to do is increase detail in all of these little local contrast areas, like the transition from this leaf on to door. With the transition from the door into the sky is going to make those more contrasty, which is going to make better detail. What I want to look out for, again, are halos.
Fortunately, most of the sliders that you'll find in Exposure Fusion don't have nearly the power that the sliders have in Tone Mapping, so it's pretty hard to come into really bad artifacting with any of these sliders. You can see it's pretty subtle. Again, if you think of Exposure Fusion working by taking your three different images and putting them into a stack and then combining them so that maybe the bright parts of the underexposed image show through and the dark parts of the overexposed image show through, Blending Point is a way of controlling am I seeing more of the bright image with its nice shadow detail, or am I seeing more of the dark image with its nice highlight detail? So this is just a way of controlling the blending of my different exposures and as you can see, for the most part it's just letting me make my image brighter or darker, but it's not a uniform brightening.
Most of the brightening and darkening is happening in the shadows. These mid-tones aren't changing too much. They are changing a little bit, but not real dramatically. So it's not like just a normal brightening. As I use it, the things I want to lookout for are, am I coming into overexposure and highlights, do I like the level of detail in my shadows? Shadows is just like the Shadow slider in the Shadow/Highlight dialog box in Photoshop. It lets me brighten shadows without doing anything to mid-tones and highlight. It's a very subtle effect and it's not even getting me very much in here.
In fact, it's mostly getting these lighter toned shadows up here in the sky. So I think I'm going to back off with that completely actually, put it back where it was. Sharpness is going to increase the sharpness of my image and it's doing it. Let's go all the way over here to the right and you can see what should look familiar to you if you ever over applied an unsharp masking filter in an image editor. I'm starting to get really pronounced halos around every edge in my image. It's giving me this garish overdone look. So this is a lot like just the normal unsharp masking tools which you will use in your image editor.
First of all it's only one slider. You don't get as many controls as you would have with an unsharp masked tool, and it's fairly subtle up until you'll get into the extreme. So this is a nice way of putting some details back into your image. As with any sharpening operation, be careful that you're not exaggerating noise. So keep an eye on your shadows and make sure they don't go too noisy. Color Saturation does just what you think. It's going to increase saturation of color. Again, this is an aesthetic choice that I can simply make for myself. In the Tone Mapping section earlier we saw on the black clippings slider. This one does the same thing.
It just clips my blacks after a certain point so that they go to complete black, which removes all detail in my shadow areas. White Clip does the same thing on the other end of the histogram and in this particular image I can go a long way before I start seeing bad clipping. So I can use this as a brightening control. I can use this as contrast control. Midtones adjustment adjusts mid- tones of my image just like the endpoint slider on Levels adjustment, so this is a way that I can get some more contrast into my image. So that is just the Fusion Adjust method of Exposure Fusion.
And as you can see, I've managed to get my brightness and contrast back where I want it. I got good detail in my highlights. I got detail in my shadows. So I've still got more dynamic range than I could have in a single image, but I don't have that full-on HDR look. Let's go to Fusion-Intensive, which gives me just three sliders. Strength, which gives me control of localized contrast, letting me add more localized contrast, which is going to bring out some more details here and there. Color Saturation, which just is a Saturation control, lets me goose up the saturation in my image, And Radius.
Radius is a little bit like the blending control that we were using in the last methods. It's biasing one exposure over another, helping me control how details are brought in from different images, basically just set this to taste, look for halos. Lowering the slider is a good way of reducing halos. Always look for noise of course. As you can see, with this method I have no brightness and contrast controls, so I can't get this image all the way where I want it, but I can get a nice control over blending. I like these highlights that I was able to bring in here and now I can take it into Photoshop and finish my brightness and contrast corrections there.
Average simply averages my images together. There are no options. I take it or leave it, and it's nice because again, I've got detail here, detail here, so I've already got more dynamic range than I would have had with a single image and I can fix the rest in Photoshop. This is basically average with the software making some decisions on its own. there are no controls for this. And as I do with any tone mapping exercise, the first thing I look for is halos, and this method produces some bad ones here, here, all around here, and here. Again, if you can't see them, look away from the image for a minute, look back at it, they'll probably be pretty visible.
Fusion - 2 images lets me take just two of the images and see what they look like when together. So I can pick what I want for the first image. So maybe I'll take 3716 and now I'm getting 3714 for the second image. I can pick another one. So basically I can just try different combinations of what two images I want and then those get averaged together. So these are my different Exposure Fusion options. Again, even if you can't remember what every single control does, first of all know that you've got this interactive help down here at the bottom of the screen.
Right there below the process button. I can't point at it with the mouse because if I move the mouse off the little Help will go away, which you can see there it says Sharpness increases the sharpness and contrast the details in the image. I'm talking about this box right down here. So that can give you a hint or clue into what the different sliders do, but also just with any tone mapping software of any kind, keep an eye out for contrast-y areas, make sure they don't have halos, and always watch for noise and make sure that it's not getting exaggerated. And of course, just keep an overall eye on how much of an HDR look do you want.
Do you want detail in every possible location or do you want to leave some shadows or possibly overexposed highlights here and there?
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