What is HDR- High Dynamic Range– How HDR Can Help You Take Better Photos
Suddenly the iPhone world is abuzz about the new “HDR” feature on the iPhone OS 4.1 upgrade. But there are a couple of other cameras on the market that also have this feature including Sony’s Digital SLRS (Single Lens Reflex with exchangable lenses) models A500, A550, A560 and A580 and Pentax K series cameras.
So, what is HDR? Did you know that there are computer programs that can apply HDR after shooting your photos so that you have the best picture?
What is HDR?
HDR stands for high dynamic range, a measurement of the range from the brightest white to the blackest black in a picture. Ideally, we could take a photo with pure white and pure black and we could see the details in all the shadows as well as in brightly lit or sky areas. Instead, typically, if the blacks are true, the bright areas will be overexposed (for example, you won’t see the clouds in a sky). Likewise, if you see the details in the highlights, details in the shadows become muddy and indistinguishable (for example, seeing the leaves in the shadowed area of a tree).
An automatic camera will expose for an average of light and dark in the frame of the photo. Some cameras allow you to pinpoint an area that you want to expose for. If you want to see in the shadows, you can point the camera at the shadow and see the photo brighten up. On the iPhone 3GS and iPhone 4, you can tap on the area of the frame where you want the best detail and exposure in the photo you are shooting. Again, if you set the camera to get the details in the shadows, chances are highlights–skies, white buildings, areas hit by the sun–will be a blob of white area with no texture or details. And vice versa.
Without HDR, you have to decide what is the most important part of the photo and expose for it. And you’ll sacrifice the details of the other areas of the photo.
HDR can fix this problem so that you get the best details throughout the photo from shadows to highlights. It does this by actually taking 3 photographs in a row. The first photo is exposed normally, the next photo exposes to get the details in the highlights (slightly underexposed) and then to get the details in the shadows (slightly overexposed). Through in-camera processing, it combines the 3 photos into a single photo. The result is a photo with details throughout the picture.
The new iPhone iOS 4.1 can do it automatically by turning on HDR. There are also apps for the iPhone, like True HDR, that will take the photos and combine them.
HDR – Using Other Cameras
If you are not using an iPhone, you can accomplish HDR by taking 3 differently exposed photos without moving the camera and then combining them using an HDR program after you upload them to your computer. The easiest way to take 3 photos with different exposures is by using a camera with Auto Exposure Bracketing (AEB). When you set the camera on AEB, it will take 3 (or more) photos–one underexposed, averaged exposure, and overexposed. Some cameras take up to 9 different exposures! Be sure to hold the camera still!
Be sure to hold your camera still– the double image of the sign is an example of moving the camera when taking the photos
But what if your camera doesn’t have AEB? Even inexpensive point and shoot cameras have exposure compensation (EC) that you can use to take the photo. Because you need to take 3 shots quickly in a row, it is best to use a tripod so the shots line up in the final combined photo.
Taking HDR Photos Using Exposure Compensation (EC)
Take the normally exposed photo, then overexpose the next photo and underexpose the next. You can do this on most cameras by taking your camera out of Auto mode and putting it into program or “P” on your mode dial (some point and shoot cameras do allow adjustments in Auto as well).
To take an overexposed or underexposed photo, find the exposure compensation (EC) adjustment on your camera. It might be a button with +/- or it may be on your LCD display. Check your camera’s user manual for how to adjust the exposure on your individual model.
To take a photo that is underexposed, adjust the exposure compensation to – 1.0 or even -1.5. You will see that the blacks are very black. Notice too, that the colors are very deep and rich. Underexposing a photo is a professional photographer’s trick for getting a very rich image.
To take the overexposed image, adjust the exposure compensation to +1.0 or even +1.5. This will “bring up” the shadows so you can see all the details. Note that the colors are now washed out, and you may not have any area with a true black. You can then use these photos in an HDR program or the HDR feature in Photoshop.
HDR Teaches Us About Ansel Adams’ Zones
High dynamic range means that you get a HUGE range of all the tones from black to white.
Have you ever seen an Ansel Adams photograph? He did the most stunning black and white photos of Yosemite, Alaska and other places of natural beauty. His photographs made these areas seem absolutely majestic. In 1939, Ansel Adams used a technique developed by he and Fred Archer called the Zone system.
The zone system is a way to choose your exposure to get the photo you imagine. Ansel Adams was asked in the 1950s if he thought the Zone System was still relevant after 10 years. He replied “If you don’t use the Zone System, then what system will you use to know what you’ve got as you photograph?”
The zone system breaks down the shades of gray into 9 zones. Zone 1 is pure white and Zone 9 is pure black. Zone 5 is known as middle gray. No film, nor digital camera to date can capture all 9 zones. Or, like I said above, if you have highlight details you won’t have details in the shadow and vice versa. By understanding the zone system, you can now control the outcome of your photograph. Different choices create different results.
If you just expose for middle gray, you won’t get pure black in the photo. The range of tones in the photograph will range a couple of shades off middle gray (Zone 5) to both sides. Underexposing the photo moves it’s middle tone to Zone 4 or Zone 3. Now your camera can capture pure black. Whites may be more grayed. Still, this is great for capturing the details in the clouds in a sky, or texture of a white flower. By the way, Ansel Adams often underexposed his photographs. (This was in the days of film so he could compensate and get better range of grays by overdeveloping the print.)
Overexposing your photo moves the middle gray to Zone 6 or above. Looking at the zones, you can see that you won’t get pure black so shadows are now brighter, you can see details or other objects that are in shadowed areas. It may also wash out the highlights to pure white.
If you want to learn more about the zone system, I encourage you to read this wonderfully, easy-to-read article.
How This Can Help You Take Better Photos?
You can take better photos by asking yourself a few questions and making a few adjustments before you snap the picture.
Let’s say you are taking a nature photo or one of a place you are visiting. Stop a moment and ask yourself:
What is it about what I’m looking at that makes me want to take this photo?
If you are shooting a waterfall, the water is important so you don’t want it to turn into a blob of white in the photo. You may want to underexpose the photo.
If you are in a forest, you probably want to see the details of the leaves and the plants in the forest. You may want to overexpose just enough to see the details.
If you are shooting a photo of a friend that is in part sunshine and part shadow, you may want to move them to all shadow or all sunshine.
Or…if you are using your iPhone, turn on HDR and get the benefits of the whole range of zones.