Image Sensor Noise

The Short Answer: Always use ISO 100 Speed (Sensitivity) available only in the Manual Modes (C1, C2, C3) .

All photographs by Michael Gordon. Page and photos copyright 2002 by Michael Gordon. Permission to copy, store, display, reproduce electronically or in print is granted for the purpose of discussion of this camera or discussion of the techniques of photography described herein. Individuals and nonprofit organizations may additionally archive and utilize these images for noncommercial purposes. First publication is Logan, Utah, USA in March, 2002. "Nikon" is a trademark of Nikon USA . "Chrysler" is a trademark of DaimlerChrysler .

This portion of an image looks a bit grainy and lacks the "snap" or crystal clarity I have been accustomed to in the Nikon 990 digital camera. At first I attributed it to the air quality at Sacramento, but there is more to it than that. (CLICK for 3x Enlargement)

(CLICK to see the original, whole image of a Chrysler PT Cruiser at the Sacramento Airport) .

To make a long story shorter, the camera had switched itself to ISO 200 speed because of a polarizer filter screwed onto the lens. The polarizer has a density such that the camera must increase exposure by two or three stops. This can cause motion blur; in automatic mode the camera compensates by increasing the sensitivity of the sensor, and this increases noise.

(Above) Here is the RED channel from the image. It is speckled, which is what noise looks like. On a large print, it is quite conspicuous. (CLICK photo or here to see 3X enlargement)

(Above) Here is the GREEN channel from the image. Notice how smooth it is. That is partly because green gets two pixels for every red or blue (RGGB).

What can you do about it? Not a whole lot; the sensor is inherently noisy (all high-resolution sensors are noisy -- TANSTAAFL applies [There Aint No Such Thing As A Free Lunch], double the pixels per image sensor diameter and you automatically increase the noise, same as using smaller film).

BUT you can make sure the camera is set to ISO 100 speed. To do that, forget ever using the "A" automatic mode. Set up one of your manual modes for mostly automatic but this allows you to specify ISO 100. BEWARE: the sensitivity is NOT PERSISTENT. That means, if you change modes and come back, the ISO will sometimes (always?) revert to ISO 200. You can turn the camera off and on; and it will stay ISO 100, but change to another mode ("A" or C1, C2, C3) and come back will set your ISO to 200.

AFTER the fact. You can polish a photo somewhat. You can polish (blend or blur) the noise in the sky using a mask and filter tool; but better results can be had by splitting the channels and blurring just the noisy channel.

RESULT:

(Above) The red channel was smoothed in the sky and side window, then recombined. (CLICK for 3X enlargement)

Return to Nikon 5000 gallery