The Textbook of Digital Photography - PhotoCourse

For more on digitAl photogrAphy, visit http://www.shortCourses.Com 37

http://www.photocourse.com/itext/noise/

http://www.photocourse.com/itext/ISO/

Click to see the effect of

noise in an image.

image sensors—sensitivity and Noise...

In some situations images are not as clear as they otherwise are. They appear

grainy with randomly scattered colored pixels that break up smooth areas.

This is what’s known as noise. It has three basic causes:

• Small photosites on the sensor. There is nothing you can do about this
  cause, but it also makes the following causes even more severe.


• A long shutter speed that lets light into the camera for a long time, usu-
  ally in a dim or dark setting, gives noise a chance to build up.


• A high ISO setting let’s you use a faster shutter speed to avoid blur but
  also amplifies the noise along with the signal.
  Many cameras have one or more noise reduction modes that reduce the ef-
  fects of this noise.

At slow shutter speeds

(left) the exposure, like

dripping water, is so

slow noise has a chance

to build up in the

image. At faster speeds,

(middle and right), the

noise is overwhelmed

by how fast the

exposure is completed.

Click to see the effects

of increasing ISO.

Noise appears in images

as random color pixels

especially when you use

long shutter speeds or

high ISO settings.

TiP

to see one kind of

noise, leave the lens

cap on and take a

picture. the long

exposure will create

noise that you can

see when you open

the picture in a photo

editing program and

enlarge it.

isO and Noise