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Photography is a process of making choices. Sometimes you've got to make a lot of difficult decisions. Sometimes you get into trouble, because you forget there are some decisions that you need to make. One of the most important decisions that you need to make involves understanding the limitations of your camera, and its ability to capture a certain range of light to dark. So I was walking along here, and I came across a shot that I like. I've got an interesting thing in the foreground, and I've got a thing in the background. Now, what I am looking at this particular scene with my eye, I can see a full range of detail, from dark shadow areas into distant, brightly-lit by-sun areas.
My eye actually has a range of about 20 stops worth of light. As photographers, we measure light in stops, every stop being one doubling of light. That gives my eye a dynamic range of a billion to one or something like that. Unfortunately, we do not have a technology that can do the same thing. My digital camera cannot do that. It cannot capture the full range of brightness values from shadows to bright sunlight. Neither can a film camera, neither in fact, kind of video camera, because it's based on the same digital imaging technology as my still camera.
Right now, you're seeing detail on me. But that bright background back there is probably washed out, but if the camera operator changes to expose for that bright background, now, I am probably in silhouette. You can see detail back there in the sunlight, but you can't see me anymore. If you were him, standing right behind the camera, you would still be able to see all of that. That's the wonderful thing about the human eye is it's got this tremendous range that the video camera doesn't. I am hoping that at some point it will come back to me, and you'll be able to see me again.
That, in this case, is the right choice, as far as exposure, as far as I am concerned. In this situation, shooting a still image, I have to make some decisions here. I have to first recognize, whoa, I am in a high dynamic range situation. I've got more levels of brightness than my camera can capture. What do I do about that? Well, I can either choose to take a shot that will show me this foreground, and accept that the background is going to be blown out to complete white. There are times when that's a good decision. There are times when that's a very evocative image, with the background burned into some kind of extreme light situation, particularly for black and white photography.
That kind of high key image can be powerful. Or I can choose to expose for that background detail back there, and just accept that this is going to fall into shadow. In this particular case, that's not going to be such a good choice, because so much of the foreground is just going to be lost to shadow. Another option is I can choose to expose for the highlights, to capture all that detail back there, and just really hope that when I get back to the computer, I can pull detail out of the foreground. The risk there is that I am not gong to be able pull enough detail out, but probably more pertinent is that when I do pull that detail out, I am going to have a big problem with noise.
There is a third option. This is a more recent option that's come about since the advent of RAW digital photography, and some very special software that's come along. That is to do something called HDR shooting, High Dynamic Range. This is a process of shooting and postproduction that allows me to capture a much greater dynamic range than what I can with single shot. So what I am going to be doing is taking a series of shots, and using special software to combine those into one image that has a full dynamic range.
So the first thing I have to do is what I would do with any other shot. I need to set up, I need to compose my shot, and frame my image. So, I've done that just like I would any other shot, using all of my same ideas of composition. Now, what I've chosen here is I've got a strong foreground element, and then I've got my background back there. Now, if I take just a single image of this, as I've said with exposing for the foreground, I get this. The camera did a good job of metering. It brought out a lot of detail in the foreground, but look at the background. It's all overexposed, and it's blown out to complete white, almost.
So, what I need to do is underexpose. Now I'm shooting in shutter priority, because I am trying to manage my depth of field. I want a lot of depth of field here. So, I am going to use my Exposure Compensation to underexpose by 2 stops. I am just picking 2 stops because I think that'll be a good amount of underexposure. I am going to take this shot, and now here I've got my background exposed well. Now, you might be thinking well, why don't you just take those two images into Photoshop and merge them, composite them somehow. I can do that, but it would be a really difficult masking job.
I'd be spending a lot of time painting around the leaves, and I am really not interested in doing that. That's the advantage of HDR is I don't get mired in a bunch of awful masking stuff. Now, here is how we pull off the HDR. First of all, we're going to be bracketing; we're going to be auto bracketing. Where my camera is in Aperture Priority mode, that means that all of my exposure changes will be to shutter speed and ISO. Whatever the camera decides to do, it's going to keep aperture where I set it. That's good. I am not going to have to worry about my depth of field changing from shot to shot.
My camera's still framed the way that I wanted. So the next thing I am going to do is turn on Auto Exposure Bracketing. Some cameras just call this Exposure Bracketing. What this does is I can set a number frames and an interval. So, I've set the camera now to shoot three frames exposed one stop apart. So, it's going to shoot a frame as metered, it's going to shoot a frame one stop under, and it's going shoot a frame one stop over. The next thing I am going to do is turn on Burst mode. This is the mode that allows me to just hold the button down, and it'll just sit there, and take pictures.
With those two modes enabled, I can notice press and hold the button for three shots, and I've got a bracketed set. Now, what you may have heard there was the shutter was staying open for a really long time. There is a problem with a long exposure image like that, which is my tripod might be shaking, the leaves might be blowing. I would really much prefer to have my shutter speed faster. But to hold the depth of field that I want, I can't change my aperture. So, what I am going to do is increase by ISO now. I am now at ISO 100.
I am going to bump it up to 400, which is going to buy me two stops of exposure latitude. Now, I am going to take another set. That was much faster there, until the end. Listening to your camera and the shutter speed that it's choosing can very often cue you into when you are possibly facing a slow shutter speed situation that you don't want to be in. So now I have got my bracketed set. Just to be safe, I am going to take another one. Here is why. These images have to be aligned with each other.
Photoshop can do a very, very good job of doing that. But still, any camera movement between images can make problems. We're going to have enough trouble with the leaves blowing around. I don't want to introduce any more trouble with camera shake. Ideally, I would be doing this with a camera remote, so that I wouldn't have to handle the camera. But I am just going to do another set just for safety. We'll be very careful here, to try and hold the camera steady. That should be good. I should be now ready to deal with those images.
I'd like to say a quick word about, yes, I am using a tripod here. You don't have to have a tripod to shoot HDR. I do lots of HDR handheld, particularly if you've got a camera with a very fast burst that can nail those images really quickly. Go back to your stabilization techniques that we talked about earlier, to be sure your shooting good steady brackets of shots. You can do HDR handheld. Obviously, if you've got a tripod, that's a better option. So, now that we've got those images, we're ready to do the merge.
We don't do that in camera. We do that in Photoshop. We've got a whole lesson on how to merge those images to turn them into a finished image with a dynamic range that's pretty close to what your eye can see.
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