“High Dynamic Range” sounds intimidating, but is not difficult to understand. In digital images, HDR techniques can be used to produce much more vibrant pictures when they reflect a wide range of brightness, say from sunshine to shadow. Even the cell phone photographer can take advantage of these techniques.
Our eyes and brain see more levels of brightness than a camera can record. One reference states that humans perceive 24 f-stops, a compact camera captures 5 to 7 and digital SLRs 8 to 11 f-stops. Images taken in RAW format, available in many digital SLRs today, can record 4,000 to 16,000 levels of brightness, compared to only 256 for JPEG images, typical in compact cameras. I will not try to explain more than this, but provide links to articles at the end of this post for readers who want more information comparing cameras to human perception.
For photographers, this limitation of cameras can result in “overblown” bright areas, in which an area is pure white, with no detail. At the other extreme, shadows will be muddy or completely black, also with little or no detail.
While we cannot give a camera the ability to record more brightness levels, there are techniques to combine more than one photograph to display more levels in the resulting image. Some of these techniques require sophisticated software and cameras; however, some can be accomplished with images from typical compact cameras.
Adobe provides Camera Raw, used with Photoshop, to combine multiple photographs into one image. There are many tutorials available on the Internet and we look at the process in another discussion. In this post, however, I wanted to show how we can use On1 Photo 10 and cell phone images to increase dynamic range. I am using a previously posted photograph, “Tree at Sunrise”, to demonstrate this technique using JPEG files.
Driving to church early one Sunday morning, I saw a stark tree silhouetted against a dramatic sunrise. In a hurry, although without a camera, I stopped, not wanting to miss the photographic opportunity.
The wide range of light values; from the bright, sun rimmed clouds in the sky to the subtle shadowy waves of grass in the foreground, and the mysterious, shrouded barn hiding in the distant fog, were not likely to be caught in one photograph. The Android phone I had with me would shoot only JPEG photos, so I quickly tapped the screen on the sky, composed and took my shot. Then I tapped the ground area, for exposure there, and fired again. I took several exposures of different places in the darker foreground and the sky. Later, I picked the two exposures with the best color, brightness and detail in the sky and the ground, one of which also had good visual information in the midranges.
There are many tutorials on using On1 Photo 10 available online, but to help visualize the technique, the basic steps are:
First, importing the two images as layers and aligning them. Reducing the opacity of the Sky layer to be able to see and compare the details of both images, and then moving the Sky layer until the smallest details line up with the image beneath. Next, using the Crop tool, adjust the frame to trim off any scraps of edge where the two images may not line up at the sides. In the Layer’s module, choose the Masking Bug, applying a horizontal bar that masks out the top layer, allowing the bottom layer to reveal itself below the foggy center of the scene. The Masking Bug allows the user to adjust the width of the bar, the transparency of the bar from zero at the top to 100% at the bottom, allowing no blocking of the grass layer by the sky layer.
I placed the Masking Bug across the area of the photos of the fog, moving it up and down, and adjusting the width slightly, until the best transition between the layers was achieved.
In each layer, I adjusted the image for the area the layer was chosen to display. In the bottom layer, I lightened the brightness, increased the contrast and the color to make the strands of grass stand out. I could not have made the same adjustments to the image exposed for the sky, because the same amount of detail was not captured in the grassy area.
Please leave a comment, or send me an email, if anyone would like a more detailed tutorial on this procedure.