What is HDR? Well Bruce Lee put it like this (Play the clip below)
Well its not about fighting, but it is about HDR. So as Bruce might have said, “It’s the art of HDR, without HDR”, and that is what we are ultimately trying to achieve.
Producing an image (HDR) without anyone knowing it was from a multi image source. So what exactly is HDR anyway, and why do we need it?
So let’s start with a premise. The human eye can see roughly what a single expose of a good DSLR camera can see. Which is about 10-
1 EV or stop, is equal to the light intensity increasing or decreasing by factor of one. So if you increase by one EV the scene will get lighter by a factor of one, or a doubling of the amount of light. If you decrease by 1 EV the Scene will get darker, because you have halved the amount of light.
So, what's the problem. Well, the human eye has a brain attached, well it does with most people! and the eyes look though the brain? Now there’s a concept: As you look around a scene, you look at all aspects, from the darkest shadows, to the brightest highlights. As you do this your iris, that part of the eye, that regulates the amount of light, is continually opening and closing. Your brain then interprets this scene and puts it all together, and that is what you see.
You can try this for yourself. Look out of the window on a sunny, or bright day, then look into your room, at something that is dark, or in the shadows. Could you see both clearly?
Now try the same with your camera, using live view. Pointing first out of the window, and then back inside. You will see the camera constantly adjusting the exposure, to try to compensate for the areas that are dark and the areas that are light. When a camera takes a picture, whether it’s full auto or manual it can only use one setting for EV or exposure value. Therefore, what we are trying to do, using HDR, to create a single image, that closely resembles, what we see with the eye. However to do that we must make multiple exposures, that can cover all aspects of the scene from the highlights, to the shadows.
Generally, if the light is good, an AEB or Auto Exposure Bracket can be set on the camera for three exposures, along with setting the drive mode to continuous. This works well hand held. Any more exposures than three, and a tripod is really necessary. Now, dependant on the scene, you may need up to nine, or even more separate exposures to capture the full dynamic range of what you can see with your eye.