Working with Grain and Digital Sensor Noise

You may have noticed some digital photographs tend to have purple dots, or perhaps bands scattered throughout the print. Usually, these distracting specks are significantly more prominent when taking photographs at night. This effect is “grain” when discussing film photography and “digital noise” when discussing digital photography. So what causes these specks and how can they be avoided? Better yet, how can you use this effect to your advantage? This article addresses these questions and offers some suggestions on how to intentionally introduce this effect.
Long before digital cameras entered the marketplace, silver nitrate film was the standard medium. Film is rated by the International Organization for Standards (ISO) to standardized the film’s sensitivity to light. As the film becomes more light sensitive, the ISO rating increases. In application, a low ISO number uses finer silver particles, which creates a finer print; however, it is significantly less responsive to light. Conversely, a high ISO number uses more course silver particles, which creates a print with more “grain,” but it is more responsive to light. Knowing this, a low ISO, let’s say 100, requires more exposure time than a film rating of 1000 ISO. Since the 1000 ISO film requires less exposure time it is referred to as a “fast” film.
When digital cameras came on the market, the industry had some degree of difficulty recruiting the traditional photographers to convert from film. Many photographers did not care to become electronic experts in order to grasp the concepts behind digital photography, so the digital camera manufacturers retained the film terminology for the ISO film standards. Although there are differences between the ISO standards, the existing film photographers found the familiarity more palatable.
Here are a few ways to avoid grainy photographs:

• Shoot at a lower ISO setting, especially at night.
• Increase your ambient light and reflective surface.
• Reduce your shutter speed and increase your aperture settings.
• Avoid backlit subjects.

Sometimes a little bit of grain is a reasonable trade-off for the advantage of using a high ISO setting. As discussed above, using higher ISO settings reduces the exposure time. Motor sports photographers have been using high ISO for years to stop motion without requiring flash units. Since motor sports photographers often use high focal length lenses, flashes become ineffective to stop motion. By increasing the ISO they can stop motion without increasing the aperture settings. Again, the photographer must decide of the trade-off is worth the effect.
There are times when a grainy shot is desired. Grain is often a desired effect to create a nostalgic effect with sepia or black and white portraits. Photographers use this to their advantage to create family albums and interesting shots. Many artistic photographers can find applications where grain is desired, but the effect is almost universally undesirable when taking night shots.
The photograph included in this article was intentionally shot at a low ISO to avoid grain, but still, as you can see, some fine grain particles were introduced due to the angle of the sun.