A mysterious creature has emerged into the dim light of the photography world, a beast few understand, most misunderstand, and some can’t stand.

 I am talking about High Dynamic Range techniques.

At the bottom you can find detailed tutorial links, but for the purposes of my little experiment I will detail it thusly:

Your eyes can see a “range” of up to 11, in the light exposure universe. Your digital CCD in you camera can only see a chunk of between 3 and 5  of that range.

HDR requires that you use your cameras auto bracketing feature to take 3 consecutive pictures, with 3 different exposure settings. Dark, Middle, and Light.

The first picture takes the first 3.5 (think of this as the dark bits - the lower third), the next, takes the next 3.5 (the midrange, middle of the road light levels), and the last one takes a picture exposing itself to the remaining higher light levels of the range.

Add this together and you get 11 in the range, so you have a  full tonal exposure of the scene, spread across three images.

If you combine the correctly exposed areas of these three pictures, you should end up with one image, which is correctly exposed across its entire tonal range. This means there are no blackout areas, no over exposed areas, and you will not lose any of the detail your eye can see!

All very well - but how do you do it? Well I didn’t havea clue so I threw myself into it in my usual blase fashion and decided to post my results here;

I took three images, which you can see here:

The first thing I discovered was that you must use a high contrast image to get the benefit, so dont try taking indoor shots unless its midsummer! I scrapped my first 15 pics, which were taken in my lounge, and went outside for more contrast!

1) As you can see in the dark one (leftmost), the brighter bits have very good detail and range, noticeably the sky. Its important to note that the tree in the foreground has almost no detail at all.

2) If you then look at the brightest (rightmost) one you will find that while the sky is now extremely overexposed, the tree is in wonderful colour and detail.

3) The middle one sits, as you would expect, somewhere in the middle ground, concentrating on the midrange of the light levels, not excelling in detail for either dark areas or light areas. This middle one is the shot you would normally be left with by almost any camera, saving to a JPG file.

What we actually want (and what our eyes see), is the sky detail from the dark one, the mids from the middle one, and the tree detail from the rightmost (lightest one). That is the principle of the beast, and you combine these together to make a single picture.

A good analogy is a car engine. It runs between 0 and 6000 rpm, but it’s power band is normally between 4500 and 6000 rpm. In order to make the car accelerate well at all speeds, we apply gears to adapt the power band of the engine to the speed the car is travelling. In 5th gear (long exposure), you cant expect the engine to pull away from a standstill (i.e. it will overexpose the bright areas - like the rightmost, lightest imge above). 5th gear is designed for 50mph and above, so it will ONLY perform well inside its “power band”. 

In the same way, a digital camera CCD has a power band, and this HDR technique is like applying three different gears, so the camera performs well at all “speeds”. A long exposure will not be any good for the light parts of the image, but will be right for the darker parts, such as the tree detail on the rightmost image.

 Using the tutorial below, and Photoshop CS3, I used the Merge to HDR function, and played with the levels. I discovered two things:

1) It really is much easier than you might think

2) Getting a good result really is much harder than you might think.

My final image appears a little washed out - This is mostly due to my human input - there are a number of sliders, and curves boxes to play with - and play with them I did. Perhaps in an amateur fashion, mostly using my thumbs and wanton abandon.

The most important thing to notice about the resultant photo is not that it looks a little washed out - thats my fault. It is that everything appears to have fully exposed detail. I am pleased with my experiemnt, and look forward to playing with more HDR scenes in the future.

 

You can see the tutorial I followed here:

You can see some excellent examples of HDR photos here: