Well this is part two of my exercise on noise. This part of the exercise took me to London at night, again using an iPhone to capture the London sky-line, shots taken in doors , two different
situations to show the effects of noise on two different surfaces. Later I will add some images taken outside at night with a Nikon D3s.
What is noise?
The first thing to say is that noise is a mixed blessing. Increasing the camera Iso setting allows you to capture images in very low light. Images that years ago we may not have been able to capture. The downside is that the image will have unwanted (in most cases) digital noise. This will appear as thousand of tiny coloured specs. It would look like grain you would have seen in very fast 35mm film.
Image noise is exacerbated by two main factors:-
- High ISO setting
- long exposures
I found a rather complicated explanation of noise in there Book Understanding exposure by Andy Stansfield (isbn 978-1-906672-99-7)
“Image artefacts caused by failure of some pixels to adequately record image data. Can be divided into luminance noise (looks like film grain) and chrominance noise (coloured pixels)
I found this rather simpler explanation on-line:-
“Image noise is the by-product of using a high ISO setting on your digital SLR camera — it is also often called “grain”. When a photo has image noise, areas of color that should
look smooth have a mottled or speckled appearance.”
So might say that a bit of noise can add to an image, a newspaper photographer may say that a picture with noise is better than no picture, especially if the image is destined for the front page!
Here are two images taken at night from the roof of New Scotland Yard, hand-held. The noise is clear
You can see that in each of the images noise is a problem. This is especially true in the black and white image.
But when you think that this image was taken hand-held, in the middle of the night, from a mile away, the image is useable.
This next image was taken at the same time, the difference, lower ISO and on a tripod.
As you can see the difference is clear.