The Limits of Digital Photography

Digital and film photography share one common goal: to capture as much subject information as possible so that it's available to work with when you make your finished print.

In film, severe underexposure results in shadow detail that's lost in clear, empty areas of film. Extreme overdevelopment creates highlight film densities that are opaque and print as empty pure white areas.

Similar problems exist in the world of digital photography, but the causes and terms we use to describe them are different.

Underexposed digital images aren't only dark and lack shadow detail, they also have dark tonal values that are contaminated with "noise" or random patterns of bright and colored pixels that degrade the quality of the image. This is especially true when you shoot digital photographs using higher ISO ratings like 800 or 1600.

This means that with digital materials you have to be concerned with both your shadow areas being too dark and lacking detail and with noise as an aesthetic factor.

For this illustration I have made the shadow area lighter to make the noise more visible.

For this illustration I have made the shadow area lighter to make the noise more visible.

FIGURE 108 Digital noise in a high-contrast image.

At the other end of the scale, film is generally more forgiving when it comes to recording high-contrast subjects.

The ability of an imaging medium to record subject contrast is called its Dynamic Range. Dynamic range is usually measured in the number of f/stops you can increase your exposure before the medium stops recording a visible difference between one stop and the next.

Black-and-white and color negative films have a dynamic range of about 8 to 10 stops. Currently, digital imaging sensors have a dynamic range that is closer to that of color transparency films, which is 6 to 8 stops.

Note: Research that currently underway promises to dramatically increase the limited dynamic range of digital sensors in the foreseeable future.

We have learned that, within limits, the highlight values of a high-contrast subject can be pulled to within the dynamic range of film by reducing the development time. "Overdevelopment" means neglecting to do this.

The term overdevelopment doesn't apply to digital camera chips, but the problems caused by attempting to photograph scenes with too much contrast are just as severe as with film.

Digital images are made of pixels or individual picture elements. Texture and detail in a digital photograph is represented by a tonal difference between one pixel and its neighbors.

If the dynamic range of your subject is too great, the light from the highlight areas will be too bright on your digital chip, which causes the tonal value of one pixel to "bloom" or bleed over to adjacent pixels. This has the effect of obliterating detail in that area of the scene. The result is a bleached out white area with no useable detail.

FIGURE 109 Blown out highlights in a high-contrast digital image.

Histograms give us a very clear way to see this effect in terms that are especially appropriate for our Procrustean analogy.

FIGURE 110 Clipping in a high-contrast digital image.

As you can see in this illustration, both the shadow and the highlight pixel values of this image end abruptly at the extreme ends of the scale.

Subject values that fall below 0 or above 255 are said to be "clipped," meaning that they are beyond the range of tonal levels that can be printed.

Once a shadow or highlight area is clipped in a digital image, the texture and detail are simply gone and can't be recovered; although there are special techniques that, within limits, can help with this problem. These are described below in the section Dealing with High-Contrast Subjects.

Digital Camera and Digital Photography

Digital Camera and Digital Photography

Compared to film cameras, digital cameras are easy to use, fun and extremely versatile. Every day there’s more features being designed. Whether you have the cheapest model or a high end model, digital cameras can do an endless number of things. Let’s look at how to get the most out of your digital camera.

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