Noise

I hate it when my pictures turn out noisy.  I always tend to shoot at low ISOs to avoid noise.  However, this isn't always possible.

What is noise anyway?

Noise resembles the graininess we see in film but can be more harsh.  Its causes are different.

The two situations where we are most likely to find noise are when we shoot using a high sensitivity setting and when you use long exposures.  Long exposures are over a second duration.

Noise due to long exposures can be remedied to a certain extent in camera by turning on the Long Exposure noise reduction feature.  I leave this on all the time because I know I'll forget to set it when I am taking long exposures.  Plus because it only affects long exposures it will have no impact on my day to day shots.

High ISO noise is less preventable.  This is because unlike long exposure noise where it follows a set pattern of pixels High ISO noise is random.  A major cause of noise is not enough photons of light striking the receptors in the sensor which causes a sampling error.  For this reason noise it at is worst in the shadow areas of an image.

As a photographer you have to decide the structures in your image that are real detail and which are noise. This can be subjective.

Looking at the image 'Grey Texture' in the resources section I feel there is a lot of noise in this section of the image. You can see the different colours in the suit, the blues, yellows and reds speckles.

However the mottling of the fabric and the folds, ribbing etc are real detail.  This is what the suit looks like.

This is an example of how noise can be subjective.

In 'Turkish Dance', taken at ISO 800, we would expect to see noise.  This noise dominates in the shadow areas.  If we look closely though we can see that this noise is on a par with the grey texture.  

In a close up of one of the dancer's face there is a lot of noise.  

In the fine detail of the silver brocade on their dresses, we can see that the detail is not present.  It is missing.

The noise in the grey texture we would expect to see due to the style of the fabric and it doesn't take away from the image.  

I feel that the noise in the faces of the dancers and in their clothes takes from the image and can't be seen truly as real detail.