Exercise: Your tolerance for noise

 

For this excersise I needed to find an image that fulfiled the following criteria:

• daylight (for the amount of light - outdoor sunlight would be too bright to allow high ISO settings, while much darker would involve long time exposures)
• A combination of sharp detail and textureless areas (such as a white wall) with some of the textureless area in shadow

The camera needed to be set on a tripod. I was to take a series of identical photographs changing the ISO setting from one to the next and cover the whole ISO settings available on the camera.

The image I chose although a little boring, just about fits the bill and means I can get on with the exercise.

The camera was set on a tripod at 24mm with an aperture of f/4.5, which in retrospect should have been increased to allow for a greated depth of field



ISO 100 0.5
The shadow cast by the black plant pot looks fine with no noise evident, as do the shadows cast by the granite bowl and the right hand corner of the fire. The vases on the top of the fire are clearly defined - although the image is a little out of focus. There is no noise evident in this image.




ISO 200 1/4
There is very little difference that I can see between this and the ISO 100 image other than maybe being a little softer (and in better focus)



ISO 400 1/6
Starting to look a little opaque into the shadows around and within the fire, the edges of the bowl are starting to blend in a little with the shadow and the reflection on the bowl a little softer. The plant pot still looks quite defined. No evidence of noise in this image.

ISO 800 1/13
This image looks quite different, the shadow from the bowl blends more into the shadow and reflection from the window is much softer. The plant pot is starting to look more opaque.




ISO 1600 1/25
Lots of noise seen in this image, even the small vases on top of the tv are starting to look speckled. The shadows in the right corner of the fire is poorly defined with the shadow from the bowl blending into each other. Noise is visible on the black plant pot.



ISO 3200 1/60
This image is a mass of noise from the pale wall, vases, leaves on the plant to the dark shadows which now include light speckles especially on the black plant pot. The noise is such that the image seems to be covered in a fine white mesh which not only affects the colour but also the form of the items in the image.

In conclusion - ISO 400 seemed to be the sensitivity where the noise started to appear at 100% magnification.

In retrospect I should have used a smaller aperture to avoid exposures of more than 1/2 as which would have introduced another kind of noise. I focused on noise that affected the pixilation of the shadows, form and colour. This was a useful excercise to see where noise is most likely to appear in an image and around what ISO level.