Nov
17

The Science and Art of HDR Photography

Introduction

There are very few arts that have had as much influence from science on their creation and improvement as photography.  Having done photography for many years now, I feel that I understand the basics of good photography. I have studied the amazing features of my D700 Nikon DSLR camera and understand how to use them well enough to get a good photo under varying conditions. I have studied composition, lighting, exposure, color and many other topics that are important to good photography.

Even after mastering the aspects of photography, there are still many scenarios where what I see or what I want to emphasize in a scene is considerably different than what is produced by taking a single photo. This is because the relatively simple mechanism by which a camera works cannot reproduce what the human eye working directly with the brain can. For instance, when it comes to capturing and processing scenes of high contrast and widely varying areas of light and darkness, the biochemical and neurological processes which lead to sight are far superior to a simple mechanical aperture exposing some film in a camera (or a photosensor in a digital camera).

Three exposures of some trees and a sunlit cloud. None show the way the scene really looked.

 Until recently, unless you had access to sophisticated and expensive film processing equipment and the considerable time and knowledge required to use it, your only alternative was to say “you had to be there to appreciate it“.  Since the early 1800′s, when photography was invented, photographers have worked very hard to reproduce what they see in their mind’s eye and have used a myriad of techniques to do this. Because of the cost, expertise and time involved, these techniques were not practical though for anyone but the most accomplished of professional photographers. That has changed.

With the advent of the personal computer, the digital camera, and ever more sophisticated image manipulation software applications, almost anyone with some time and a little study can learn to adjust images taken on their digital cameras, including those with highly varying light and dark areas, to produce first class photos. Now you and I can recreate those scenes photographically that previously required the image plus an embellishment of verbal descriptions of how beautiful it was to get the point across. This technique is called High Dynamic Range Photography or simply HDR.

A more realistic image created from the three exposures using HDR photography techniques.

 What is HDR Photography?

HDR photography is a method of combining different exposures of the same scene to allow the photographer to capture a wider range of tonal detail than could be captured by a single shot. Since photography was invented in the early 1880′s, one of the classic problems that photographers have faced was creating a photo that was representative of what the eye could see in scenarios where the shot included areas of intense lighting as well as very dark areas. In such shots the resulting photo might show adequate detail in highly lit areas but the darker areas would all be very dark or black with little or no detail. Alternatively the shot might show detail in the darker areas but the lighter areas would be washed out with little detail.

 Camera vs the Human Eye

Three exposures taken of a poorly lit room which were used to create a composite image using HDR photography.

Dynamic range for a camera can be described in terms of Exposure Value differences between the brightest and darkest parts of an image. In a camera, a combination of the shutter speed and aperture setting controls the exposure.  One purpose of the aperture of a camera is to control the amount of light that is allowed to enter the camera. This limits the brightness of the image by restricting the size of the aperture to stop some of the light from entering the camera. Rather than allowing continuous control of the aperture size, cameras allow the photographer to increase or decrease the size of the camera’s aperture in discrete steps. These are called stops. As you go up the stop scale for a camera, each stop allows 1/2 the light intensity to enter the camera as the previous stop. I did a survey of several photography oriented websites and the consensus regarding the dynamic range of cameras vs the human eyeball measured in stops are as follows. Most point and shoot compact cameras have a dynamic range of 5-7 stops. Most high end SLR cameras have a dynamic range of 8-11 stops. The human eyeball static dynamic range has been estimated to be between 10 to 14 stops.  Given a minute or so to adjust, the human eye can see a total dynamic range of approximately 20 stops.  This is much higher than even the best SLR camera image.

Why do we see more dynamic range than what is shown in the photos we take? It mostly has to do with our brain’s interpretation of the image transmitted to it by the eyeball. The brain and eyes work together in real time to evaluate multiple exposures in a continuous way such that the mind’s eye sees an image that is far superior to what the camera is mechanically capable of capturing in a single moment.

Interior room imaged processed through HDR techniques has much better lighting characteristics.

HDR Photography Can be Learned by Almost Anyone

Due to the great image manipulation tools that have emerged in the last 10 years, HDR photography can now be done by anyone with a camera with basic features like aperture and shutter speed controls. There are a couple of free software applications available for doing HDR.   For the better HDR software you will need to spend from $30 – $700 in software tools depending on how good you want the resulting images to look. Most of these tools offer a 30 day free trial if you want to try this out. There are lots of websites that explain how to do HDR photography in detail so I will just briefly go over the process based on some photography that I did recently that required HDR to make them look correct. For anyone that wants to learn how to do this in very detailed steps, check out the links at the end of this post.

 The Process

  1. Take at least three photos of the same scene but with different exposure settings. One will be taken at the “ideal” exposure for the scene as determined by a light meter or automatically by your camera. One will be taken one F-Stop below the ideal exposure to create an over-exposed photo. One will be taken one F-Stop above the ideal exposure to create an under-exposed photo. Most high end cameras allow you to do this automatically using a feature called automatic exposure braketing.
  2. Move the images to your computer.
  3. Use an HDR software application to merge the photos and adjust the tone mapping using various controls to achieve the desired look.
  4. Correct various problems that are sometimes introduced in the process of merging the photos. Among these are (a) ghosting caused by things moving while you were taking the shots, (b) chromatic abberation caused by the camera lens reacting to different wavelengths of light by offsetting them in shots that were taken, (c) noise that shows up in some areas of the photo as pixels of various colors. There are automated tools that allow you to fix all of these.
  5. Save the image and post it to the desired medium.

The detail of the clouds and the beautiful colors of the foilage cannot be captured in the same image.

 Examples

The examples included with this post include a landscape shot with some trees and a beautifully sunlit cloud, an interior shot, and a landscape with some menacing storm clouds. I have included three shots of different exposures for each along with the final HDR photo. For the shot with the trees and the brightly lit cloud I was able to show the beauty of the cloud with the orange highlights from the late afternoon sunlight while lighting up the trees so that they didn’t show up as a bunch of dark shadows. For the interior shot I was able to use HDR photography to enhance the lighting in the poorly lit room without having to use a bunch of expensive lighting equipment.  For the landscape with the menacing storm clouds I was able to bring out the details and textures in the clouds while still being able to show the color of the trees. It takes a little more time and work to do this but as you can see it is worth it to get a final image that represents pretty much what I saw with my eyes.

With HDR techniques we can capture both the cloud texture and the beautiful foilage colors.

Still a Way to Go But We’re Getting there Fast!

Even with the amazing technology of HDR photography, it is still not quite as good as the eye can see. The physical mediums that we currently use to view photographs like film, high resolution monitors, etc. do not have the dynamic range of human sight. To resolve this issue, HDR techniques currently reduce the range of contrast for the photo while allowing more detail to be seen in the brighter and darker areas than in a traditional photograph. This results in some darkening up the brighter areas and lightening of the darker areas. This means that a really good HDR photograph is tuned to the medium that it will be displayed on. As time goes by though, improvements will be made both in image manipulation capability and in the output media to increase the dynamic range of what can be displayed.

We are already seeing cameras come out with an HDR mode that allows the photographer the option of doing HDR photography in real time with no post processing. The i-Phone 4 was one of the first devices to offer this option on its camera and it works reasonably well considering all you have to do is point and shoot. Now all the major digital camera manufacturers have at least one camera model that offers this feature. Still, if you want to be able to produce amazing HDR photographs on the order that some of the best HDR photographers produce, you will need to invest in a good digital SLR camera as well as some of the software mentioned below and spend some time learning the techniques involved. To me it is certainly worth the investment in both time and money.

Links of Interest and Further Information

Photography Basics

About.com – Photography Basics Article  - Offers a good discussion of the basics of good photography.

LifeHacker Article – How a Digital Camera Works

Photography Basics – A very good photography basics article.

Digital Photography School – A good site with tutorials. Also allows you to submit photos and get the critiqued and to write articles.

The Luminous Landscape – One of the web’s most comprehensive sites devoted to the art of landscape, nature and documentary photography using digital as well as traditional image processing techniques.

The following are four good posts from the same website.

Digital Photography Basics: The Camera

Digital Photography Tips for Beginners

20 Must-Reads for Amateur Photographer

Top 8 Photography Websites

Great Image Software Tools for Producing HDR Photography.

Top 10 HDR Applications for 2011

Essays on What the Eye Sees vs What the Camera Captures

http://www.luminous-landscape.com/columns/eye-camera.shtml

HDR Photography Tutorials

http://www.stuckincustoms.com/hdr-tutorial/ - One of the better HDR tutorials on the Internet.

19 Good Tutorials for Doing HDR Photography

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