ISO and Visual Noise

Left and right: Low (80) and high (1600) ISO — an extreme example to make a point. Spider & Skeleton art by my friend Tre Roberts, photographed in my front window with lots of sunlight on the other side and not much on this side. Note the low noise and high contrast in the low ISO shot on the left and the high noise and low contrast in the right image.

Film and other materials are rated by the International Standards Organization (ISO) according to their relative sensitivity to light. If you use film, use slow film to photograph art. If you use digital, set the camera to a low ISO setting.

We used to call this sensitivity "film speed" or "ASA" (American Standards Association), and it is still expressed as a number, with lower numbers indicating less sensitivity.

With either film or digital, the lower the speed, the lower the visual noise and the higher the contrast. Conversely, the higher the ISO, the higher the noise and the lower the apparent contrast. Grain looks like noise in the image. Fine grain usually looks better than coarse grain.

In film, visible grain was a clumping of light-sensitive silver halides suspended in the hardened gelatin of the film.

In digital, the same effect is caused by other factors, which can be somewhat controlled in PP (Post Production) via image-editing software or a plug-in noise-remover. In digital that "graininess" is called visual noise, which comes in two varieties — color noise and contrast noise — with essentially similar results that look a lot like film grain.

I often use Nik's DFine plug-in for the full-blown (and expensive) version of Photoshop, but there are other noise-reduction plug-ins that work with that and other programs. Photoshop Elements is a good, inexpensive — about $70 — program that will probably suit your art-photographing needs at first. Using digital photographs without editing tends to look amateurish and does not show your art to its best advantage.

At the least, you should correct the tonal range, contrast, color saturation and composition of your images, although more discussion of those techniques is beyond the scope of this article. (See Levels, below.)

80 or 100 is the lowest ISO available on most digital cameras, although 200 is the base ISO of my dSLR. Some even very expensive digital cameras render images that are so noisy at any rating higher than 100, that they are unusable for photographing art. Newer, better and only sometimes more expensive digicams can render images at higher ISO ratings very well. Most professional camera reviews show sample photographs at different ISO settings.

Some cameras are much better than others at controlling noise in high-ISO photographs.

I'll repeat: in general, it is best to use low ISO camera settings when photographing art. Putting the camera on a firm, secure tripod is also recommended