This photo of the interior of John Burroughs’s writing studio illustrates a fundamental limitation of photography.
The view out the window is so bright that it has burned out (or “clipped”) to white, and the shadows in the corner are an impenetrable black. In both instances, the optical sensors are unable to record any meaningful color data. But in real life, our human eyes could see plenty of color and detail in both areas of the view.
The problem is that the camera, whether film or digital, can only record within roughly a 300/1 ratio of light intensities, while the human eye can easily respond to a range of 50,000/1 within a single scene.
The range of intensities is called the dynamic range. The camera is not the only thing with a limited dynamic range. The same 300/1 ratio also applies to digital printers, computer screens, or artist’s pigments.
It’s analogous to the problem you’d have playing Beethoven’s Ninth over a cellphone.
Photographers have found a way around the problem. By taking several different exposures of the same scene (one shot exposed for the bright sky and another for the dark shadows), the photos can be combined, or “tone-mapped” into a single image where every part of the scene is visible in rich, glowing color.
Here is a photo of a room interior with a normal exposure.
With tone mapping in HDR photography, color is saturated and detail is present throughout the image.
The effect of HDR can look a bit garish at first, partly because we’re not used to it, but also because it can take away the excitement of strong contrast. But in artistic hands, it can also be otherworldly and attractive, reproducing the feeling of what an artist might see, with color and detail infusing the entire scene, both in the shadows and in the blue sky.
The real frontier for HDR photography will be the new brighter computer screens, like the new BrightSide technology, which will be able to output HDR image files in their true range of brilliancy, giving the viewer the feeling of standing in a real street in the bright sunlight.
What does all this mean to painters? Although our eyes can see greater dynamic range than the camera can see, we’re still forced to translate our observation through the measly 300/1 funnel of pigments on canvas.
When you're painting subjects in soft, overcast light, it's easy to convert reality into paint. But when you have subjects with extreme tonal contrasts, like views out windows, or illuminated signs at night, a successful painting requires a keen awareness of the distribution of tones.
Flickr HDR groups, link and link.
Wikipedia on HDR imaging, link.