This is the first part of a two-part series on creating High Dynamic Range Images (HDRI) from a single exposure, written for the Canon Digital Learning Center by Ron Berard:
- Part I: Capturing and DPP Processing Techniques
- Part II: Processing and final image manipulation (click to read)
My interest in High Dynamic Range (HDR) all started when I saw a photograph on an Australian photographer's web site. It was a somewhat panoramic shot of a beautiful landscape, with a gorgeous early evening sky. The sun was setting in the lower right hand corner of the frame. The sky colors were rich and detailed, and so was the landscape. I asked myself, “How was the photographer able to get vibrant and sparkling green grass, not to mention unbelievable detail in the mountains, and still keep the sky from being blown out of the photo?” Sure, maybe he masked the sky in Photoshop using the selection tool, and then brought back some color and detail, but not to these extremes. This made me think of all the colorful shots I could have captured in Manhattan with its gorgeous, detailed late afternoon skies. The problem with this is most of the foreground objects (buildings, streets, pedestrians, automobiles, etc.) are all shaded because the tall buildings block out the sunlight. So to compensate for the darker areas, the sky becomes severely overexposed and blown out.
On this photographer’s web site, he briefly mentioned a process called “High Dynamic Range.” This technique, he noted, was able to bring back the richness of the skies and any other overexposed areas in the images. It still didn’t explain how it was done or how he was able to add so much saturation and shades of colors that didn’t seem to belong there, yet looked terrific! It took me a while to gather enough information on HDR so I would know how it’s done, and what I needed to do, or to, buy to get myself started. Of course now you cannot pick up a photo magazine without spotting an article on HDR (for instance, in the July/August 2009 issue of Photoshop User magazine, the cover highlights HDR as a “FAD or FUTURE” of digital photography).
What is High Dynamic Range? It means a broad range of light that can be measured and recorded by a single exposure. Very seldom can you get an entire range of light in one single photograph, particularly with scenes that contain a lot of contrast -- bright widows and a dimly lit interior, or a sky against shaded mountains, for example. There is always something lost in the process, some over- or under-exposed as with the examples above. HDR processing makes it possible to restore those lost highlights and shadows in a scene. In addition, the color hues and tones produce vivid colors never seen before in an image. All of this can be done without any artificial lighting.
Here is the typical approach to HDR photography: By taking multiple images of the same scene at various exposures using Auto Exposure Bracketing (AEB), the images can then be blended or merged together in the software. By shooting numerous images, usually three to nine different shots of the same scene at various exposures ranging from extremely under- to extremely overexposed, the HDR software merging of these images recaptures the brightest and darkest details that would have been lost in a single exposure. The dedicated HDR processing software takes all of the merged images and creates its own photo file as a very large 32-bit image -- to hold all of the pertinent information needed to express the entire light range in the scene. The software also realizes that most computer monitors cannot correctly show this image range, so a second process called “tone mapping” transfers the 32-bit file to a range viewable in 8- and/or 16-bit. This final image file produces an incredible range of colors and detail throughout the scene in both highlights and shadows.
This traditional approach to HDR (taking multiple exposures of a stationary subject at different shutter speeds or exposure compensation levels) requires a tripod to keep the camera stable because it is imperative that the images line up exactly, overlapping one another. Note, also that ideally the subject itself is ALSO stationary -- meaning for traditional HDR to work most effectively, it is preferable to have absolutely no movement in the image at the time of exposure, from the camera or the subject. Landscapes and scenic panoramas have therefore become the choice subject of HDR imaging. Other subjects, such as streetscapes, portraits, or any kind of photojournalism pose several challenges to traditional HDR. The most common issue, of course, is 'ghosting'. Ghosting is the result of camera or subject movement from people, cars, bikes, animals, even wind blowing through trees, etc; when multiple images are merged, if anything has moved from frame to frame, that movement will appear in the final HDR file as indistinct blurs or as soft 'ghosts' staggering away from the main subject. Some of the current dedicated HDR software options offer ghost correction, but only to a point.
There are, of course, a few downsides to HDR. One main problem is noise. In the old days of film we used to call it “grain.” When an image approaches the dark end of the 0~255 brightness scale (approaching 0), that’s when noise is most prominent. On the other end of the scale, where it’s at its brightest (approaching 255), color shifting becomes present. Today’s high-end cameras with large imaging sensors sch as the EOS 5D Mark II or EOS-1Ds Mark III have an advantage here, because large pixels tend to control noise and color shifting much better. Another drawback is the relatively limited options of appropriate, stationary subjects (at least, when using the more traditional bracketed, mutli-exposure approach to HDR). That, and having to lug a tripod wherever you go! I know a few photographers who live out in the country and love walking all over the place with their sturdy tripod on their shoulder, looking for just the right landscape -- that's great for them. But it's not so easy for me, walking on a crowded Manhattan street, setting up a tripod as people constantly walk by, obstructing your view and knocking into you. For me, that freedom of movement -- mine, and the subject's -- is the real appeal of single image HDR. I would say about 90% of my HDR images were created from a single exposure. Some say the results from this single image process will not be as dramatic as those created from multiple bracketed images. Whether or not you agree, there is one little secret I use as my last processing step that creates an image that rivals or even surpasses the effect of traditional bracketed HDR images -- this is discussed in Part II of this tip.
What kinds of scenes make the best candidates for HDR? Obviously, those with a broader EV scale. Look for three types of light in an image: brightness, luminance and reflectance, mixed in with dark areas. Most photographers dislike images with extreme contrast, but in HDR, these images can sometimes become the best type of shots. The question then becomes how distinct and separate are the bright and dark areas in the image. One example is a photo of an interior of a room or building with a view looking out through a window into a bright light outdoors.
An image with a certain amount of shadow area, and in that shadow area are some bright areas, working into a background with highlights and detail. I guess this is my view of what street life in Manhattan on a late afternoon is like: The shaded buildings and street with a few bright areas of people walking through an intersection. And above, a beautiful dark blue afternoon sky with little white puffy clouds.
What equipment is needed for HDR?
First of all, a digital camera. When I began I shooting this I used a Canon EOS 20D. The camera did a great job, even with only 8.2 megapixels, the images were tack sharp, however, my HDR software had to work hard sometimes to control the noise factor. Recently I switched over to the EOS 50D, the noise factor is almost nonexistent. Of course, Canon's Noise Reduction (which can be applied to RAW files in Digital Photo Professional software) helps, and there are also third-party plug-ins that do a great job.
A tripod is a must for traditional multi-exposure HDR. What kind of lenses work best with HDR photography? The same lenses you would use for panoramas or landscapes. My personal choice would be a wide zoom, such as the EF-S 10-22mm f/3.5-4.5 or the EF 17-40mm f/4L lens, or perhaps a more standard lens like the EF 24-105mm f/4L zoom. The more area you can get in your image, the better.
Finally, I strongly recommend you shoot your images in the RAW format, if at all possible. The JPEG and TIFF formats will also work but because HDR is all about as much information gathering as possible, RAW is the way to go. Shooting in JPEG, by far, will not provide the same image adjustment options that RAW will give you.
The Single Image Process
This involves taking a SINGLE RAW image, and processing it three separate times — each time varying the brightness/exposure in the RAW processing software to produce three separate files (of the same original image) with very different exposure characteristics. Then, these three processed files are brought into a dedicated High Dynamic Range software, to be merged into a single, finished image. The single image process has one huge advantage: scenes with motion can be converted into a finished HDR image, with no worries about “ghosting” or other problems.
Because HDR relies on as much information as it can get, RAW files are unquestionably the best ones for this purpose. Make sure your image is properly exposed. I tend to shoot mine slightly underexposed (not more than 1/3 of a stop). Bring your raw file into Canon’s RAW Image Processor, Digital Photo Professional (DPP). Double click on your thumbnail image file to bring into larger view in a separate editing window.
Like most RAW file processing software, Digital Photo Professional’s RAW processing tools include a brightness/exposure slider. This should be dialed at 0.00. I then set my contrast, highlight, shadow, color tone, color saturation and sharpness scales according to my tastes. When I am satisfied with my settings, I want to process this RAW image and save it as a 16-bit .tif file.
Click on FILE > CONVERT AND SAVE in DPP. I saved the file in a folder and named it _MG_6052. This is my properly exposed image. I will then go back into Canon’s Digital Photo Professional and notice my settings are the same as I left them. I’ve decided to convert only three images for this presentation, one normally exposed, one two stops overexposed and one two stops underexposed. I will then go to my “Brightness Adjustment Scale” (upper right corner) and move my slide to a two stop overexposed image to 2.00. You will notice the picture lighten up considerably after setting the scale to the extreme right.
All of my other scales stay the same. This is a must in HDR blending and merging. After your first properly exposed image is brought into DPP and set, do not alter any of your following images in any way shape or form (except for the “brightness adjustment” setting). Then click FILE > CONVERT AND SAVE, I pointed the software to my folder where the other tiff file was saved. I named this intentionally over-exposed file just like the previous one but added the letter “B” (below). Click save and then go back in to Canon’s Digital Photo Professional. This time take your slider from your “Brightness Adjustment” settings and slide it from its present 2.00 setting to the other extreme at a -2.00 underexposed setting. You will notice how the image darkens as you make this 2 stop underexposed setting.
With all of my other scale settings remaining the same, I can then save this final image into my folder as a 16 bit .tif file named the same as before, but this time adding the letter “C.” You will notice I now have three tif files saved (in this example, named _MG_6052.tif, _MG_6052B.tif, and _MG_6052C.tif). These three files will then be imported into my HDR software for merging and tone mapping.
The Multiple Image Process:
This is the traditional method to produce finished HDR images. Three, five, or more separate pictures of the same subject are taken, processed in your RAW file software, and then those separate finished images are brought into a dedicated HDR conversion software program to produce a single, final HDR image.
The importing of multiple RAW images into DPP are almost the same as a single image, with a few alterations. First, you need to already have your odd number of images shot at different exposure levels (hopefully with a tripod). For this particular demonstration, nine images were shot at 1/2 stop increments. The nine images can be seen inside the DPP RAW software (in this example, they are numbered _MG_6362 to _MG_6370).
Double click on the first image in the series (_MG_6362) to make it larger. In this particular configuration of multiple images, none of the scale settings on the extreme right side of the screen are altered. Just make sure your Brightness Adjustment settings is set at '0.00'. Now you want to convert and save the image as a 16-bit .tif file in a folder of your choosing. I am just going to name this file as _MG_6362.tif.
You will then go back to your DPP screen and click on the second image. Enlarge it by double-clicking the thumbail (again, make sure none of the sliders to the right are moved and double check that the Brightness Adjustment settings remain at 0.00). Again, click on FILE > CONVERT AND SAVE. Save the image in the same folder as the first image.
Keep repeating these steps throughout all nine images. You will eventually get to the final image. When you are ready to save it, make sure your folder shows all other eight images (in this example, _MG_6362.tiff through _MG_6369.tiff) when you bring in the final image (to be save as _MG_6370.tiff)
You can now get out of Canon Digital Photo Professional. You will now have all of your 16-bit .tif image files ready to bring into your HDR software for the final and most exciting steps of merging and converting these images to a work of art. For more information about the traditional bracketing method of creating HDR images, you can check out this tip series on the Canon Digital Learning Center: Capture More Light, by Uwe Steinmueller.
HIGH DYNAMIC RANGE SOFTWARE:
There are numerous software applications for HDR. The two I favor are Photomatix Pro, by the HDRsoft company (www.hdrsoft.com). The second is Dynamic-PHOTO HDR, by a company called Media Chance (www.mediachance.com). Both do great work, although a majority of users probably use Photomatix Pro, as it has a broader range of functionality. There is another application that does unbelievable work in HDR called LucisArt by a company called Image Content Technology (www.lucisart.com). There is almost no learning curve involved with this plu-in software, as all of its different features are just “click” and watch it develop; but it is expensive. Aside from these recommendations, there are lots of other third-party software options to specialize in HDR processing, and most of them offer free basic or trial version -- so try them all, and see which one works best for you.
In Part II of this project, I go through the various post processing options of images as they are merged in HDR software and finalized using Photomatix. I then throw one last plug-in into the single-image HDR files, sharing my secret to creating merged images from one shot that rival the traditional method of shooting HDR.
Ron J. Berard is a photographer based in New York City since 1997. Originally from Louisiana, Ron has 35 years as a professional photographer. His photographs have been published in major magazines, newspapers and books. To see more of Ron's work, visit his web site www.berardway.com
The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.
All images are copyright Ron Berard