High Dynamic Range

high dynamic range photo
High Dynamic Range is a technique help you to get impressive images that exceed your camera’s capability.

Dynamic Range means the limits of luminance range that a given digital camera or film can capture; the number of “steps” between the brightest and the darkest area that the camera can capture.

dynamic range example

High Dynamic Range Imaging Example

Why we need high dynamic range? Let’s use some common examples to explain what benefit you can get from employing High Dynamic Range techniques.

high dynamic range example 1 original

This is a very common example that an object with light color in the middle of darker color scene. Most of us would took a picture that looks like the one above; good exposure for the trees and the lake, but hut would be over exposed (or oppositely, good exposure for the hut, under exposure of the trees and the lake).

Lighter color objects reflect many time more light than dark color objects, so the brightness of the hut is a few steps higher than the rest of the scene.

Here is an picture taken at the same scene with High Dynamic Range technique.

high dynamic range example 1 HDR

Now you get a image with the best exposure for the hut, also with best exposure for the trees and the lake. The different is very impressive, even dramatic.

High Dynamic Range Imaging Example 2

If you like traveling, you may have chances for visiting churches / cathedrals. Usually those churches / cathedrals are built centuries ago, and inside the church, the main light source during the day would be sunlight from the windows.

high dynamic range example 2 original

We could expect to take a photo like the one above, good exposure for the interior, but because sunlight coming from the windows, over exposure for the windows. Because the light intensity from the windows is much higher than the light reflected from other object.

Again, if you apply High Dynamic Range Imaging techniques, you could get an image like this.

high dynamic range example 2 HDR

In fact, this example is a bit too dramatic, because the HDR version image captures perfect exposure of all the object in the scene. It is even better than what you may see with your own eyes; or I can say, that is unreal. However, most people would like the HDR image more than the “normal” one.

How to take High Dynamic Range Image?

Film Age HDR Imaging

During the film era of photography, graduated neutral density filters were use to increase the dynamic range of scene luminance that could be captured on film. The filter was positioned in front of the lens at the time the exposure was made; the top half was dark and the bottom half was clear. The dark area was placed over a scene’s high-intensity region; usually the sky.

graduated neutral density filter

The result was more evenly exposed film with increased detail in the shadows and low light areas. Though this didn’t increase the fixed dynamic range available at the surface of the film’s emulsion, it stretched usable dynamic range in practice.

Digital Age HDR Imaging

When digital photography became popular, many people developed algorithms that mapped the image and adjusted the signal gain of the pixels in shadows and in highlights to better distribute the lighting range across the image

There are several ways to achieve HDR in digital age, let’s start with the easy ways.

Camera built-in Dynamic Range function

Many new cameras are now come with Dynamic Range enhancement feature; Sony’s Dynamic Range Optimization on A900 or Nikon’s D-Lighting on D700 are designed to enhance the dynamic range of the picture.

Camera built-in HDR function OFF	Camera built-in HDR function ON
Crop of Camera built-in HDR function OFF	Crop of Camera built-in HDR function ON

This sample picture was produced by Nikon D700. You can see that camera built-in dynamic range enhancement feature dose help, but the result is not significant.

Photoshop – Shadow / Highlight function

For cases where the brightness different between the brightest and the darkest area is not too much, you can use Photoshop’s Shadow / Highlight function to selectively make the dark area brighter or make the bright area darker.

Original picture

Enhanced by Shadow / Highlight

HDR enhanced by generating 3 JPEG from 1 RAW file

This example gives you an idea of what shadow / highlight can do. By making the shadow area brighter, the picture shows much more details of the dark area which was not able to see in the original picture.

The picture on the left is an example of High Dynamic Range enhancement technique. It was done by using 1 RAW file, tuning the exposure to +2/-2 EV, generate 3 JPEG files with raw conversion software like Canon’s Digital Photo Professional. And then, put all 3 JPEG file (+2 EV / 0 EV / -2 EV) into a High Dynamic Range enhancement software like Photomatix or EasyHDR.

From the sample photos, you can notice the HDR sample photo shows more details than the shadow / highlight sample photo. However, the high ISO noise is much more noticeable in the HDR sample photo.

Using High Dynamic Range enhancement software

In fact, if you would like to do some serious HDR imaging, you need some software that is specialize in HDR enhancement. These softwares are developed with special algorithms to map / calculate HDR images. And, these softwares are usually consume a lot of processing power and memory.

Basic idea of multi-image dynamic range enhancement

The idea is quite simple, since cameras are not able to capture all the information in one picture, we can take a few pictures with each picture focus on certain brightness range, then use software to extract / combine the sweet fruits together into one perfect photo with all the details.

high dynamic range photo from 3 images

The idea is simple, but it take some very complex mathematics to determine / map the desired pixel details together. This is why usually those HDR enhancement software use up a lot of resources.

Lazy way: 1 RAW file High Dynamic Range enhancement

The most effective way to enhance dynamic range would be taking 3 to 5 picture with different exposure settings, which would provide the richest information for HDR software to do the best job.

However, it is interesting to know that, in fact your camera’s sensor capture much more details / dynamic range then you can see in a image.

Original Picture	Same picture but tuned -2 EV in RAW format
Crop of the original photo	Crop of the -2 EV photo

You can see from this example that RAW format image contains more details than a “normal” picture can show. That is why new cameras come with HDR enhancement features.

That is why you can get a better picture from tuning and converting 1 RAW file into 3 JPEG file with +2 EV / 0 EV / -2 EV then combine into one HDR image with HDR enhancement software. This is the same thing as the camera built-in DR enhancement function does, but the HDR softwares employ a lot more complex and accurate mathematics / algorithms with unlimited computational resource to produce a better result.

Multi photos High Dynamic Range Imaging

To get the highest dynamic range, you should take use “exposure bracketing”. Exposure bracketing is a common feature on DSLR that allows you to take a few photos with different exposure settings at once; usually a range of -2 EV to +2 EV, 3 to 5 photos. For the case of 5 photos exposure bracketing, it could be -2 EV, – 1 EV, 0 EV, +1 EV, + 2 EV.

hdr sample - made from 5 images

All you need are:

Tripod – to make sure you can get 3 to 5 images that are align / at the same position
High Dynamic Range Enhancement Software – Photomatix / EasyHDR / Photoshop

In fact, you can make HDR images with DSLR or DC. If you use DSLR, it is easy, use the exposure bracketing feature and you can get 3 to 5 images by pressing the shunter once. If you use DC, you would need to use manual exposure settings and take 3 to 5 pictures manually.

High Dynamic Range Imaging softwares

You can use Photoshop to make HDR images, try using “File > Automate > Merge to HDR”. It will let you choose a few photo files, then press OK…. that is …. you don’t have any control on the image mapping / tone mapping. The result is just OK, not great.

If you would like to get great HDR images, you may try specialized HDR softwares like Photomatix or EasyHDR. They are famous, and they don’t cost a lot, yet they are quite similar. With Photomatix / EasyHDR, you can control the image mapping / tone mapping settings, and these specialized software employ state-of-the-art algorithms to map / calculate HDR images; you would get better result than Photoshop.

hdr software step 1

The 2 images above are screen shoot of Photomatix. It is very easy to create a HDR image, just select a few images, Photomatix would automatically read the EXIF for exposure data, if exposure data is not available, you may be asked to input exposure data manually.