Question:
Why are my pictures grainy?

Answer: The quality of an image produced by any digital camera can vary due to the exposure of the image. This can actually vary from image to image because the shooting environment may vary.

The way in which a digital sensor performs has an effect on how an image is captured. The pixels (picture elements) in the sensor are photodiodes that use an electrical charge to capture the image, which is then converted to the digital data that is saved on the memory card. The ISO (think of ISO as film speed) is varied by the gain level on the sensor—the same as changing the volume on a stereo. At a low ISO, the gain (voltage) is relatively low, and the picture will not appear to be grainy. As the ISO is increased, the gain level is increased to make the sensor more sensitive to light. When the gain level is increased two things occur—the sensor becomes hotter and the electrical charges in the microscopic wells that the photodiodes are in spill over into adjacent pixel wells. The result is the graininess you see, which is referred to as digital noise. Digital noise will also increase during a long exposure because the sensor is energized longer. Since low-light scenes require longer exposure, more noise will result in low light compared to a shot taken in bright sunlight or with a flash, which use shorter exposures.

DIS (Digital Image Stabilization) reduces the effects of camera shake and subject movement by varying the ISO automatically, resulting in shutter speeds that freeze the action. In well-lit situations, DIS does not need to use a high ISO to arrive at suitable shutter speeds, but in low-light situations DIS may have to increase the ISO (and sensor gain) to a higher level to arrive at a suitable shutter speed. The higher ISO will result in more digital noise, which will appear as graininess.

The best way to reduce digital noise in low-light situations is to use the flash rather than shooting with available light or set the flash to AUTO or Red Eye. Another practice is to not use the AUTO ISO, but select a moderate ISO or an ISO suitable to the shooting scenario. Also, if you learn to use the SCENE modes, the modes will select ISOs appropriate to the shooting scenario.

Your camera may also have a NOISE FILTER and/or a NOISE REDUCTION option in the camera menu that will digitally clean up digital noise with a small loss of image detail. If the camera has a SHARPNESS menu option, setting it to –2 will yield a cleaner image since sharpening may exaggerate digital noise by sharpening the edges of the “grains.”

One trick for cleaning up digital noise in shadow areas of downloaded images is to use the Tone Curve function in the Edit Palette of the OLYMPUS Master 2 software bundled with the camera. Put the cursor toward the bottom of the red line, and while holding down the left button on the mouse, pull the line downward slightly. This will make the deepest shadow areas darker which will clean up the “smoky” texture of the shadows caused by digital noise.

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