This exercise looked at digital noise, the situations when noticeable noise appears, the way it manifests in images and how to manage the negative effect it might have on the quality of images.
Following the instructions given in the Exercise 3, I made a sequence of ten images, changing ISO setting so that each image is one ISO setting apart from the previous.
All images were shot at f/8, 100mm.
Image1
The image was exposed for ½ second at f/8, ISO setting 50.
This is the ISO setting that I usually use and I am very comfortable with the quality that this setting delivers. There is no visible noise even at higher magnification.
The image was exposed for 1/4 second at f/8, ISO setting 100. I use ISO 100 when the light conditions deteriorate and it is no longer possible to use ISO 50.
The 1:1 magnifications show reasonable level of detail and sharpness delivered without sacrificing the colours and quality of the image.
Image 3
The image was exposed for 1/8 second at f/8, ISO setting 200.
Image 4
The image was exposed for 1/15 second at f/8, ISO setting 400.
The noise in the shadow areas of images 3 and 4 increased marginally. Both pictures still look sharp and the colours look properly represented when viewed without any magnification. At 1:1 magnification, a slight loss of detail and a marginal increase in ‘graininess’ is apparent. I found the amount of noise at these ISO settings tolerable.
Image 5
The image was exposed for 1/30 second at f/8, ISO setting 800.
Although the amount of noise increases at this ISO setting, I found that the quality of the image remains reasonably good. 1:1 magnification shows some loss of sharpness, particularly around the edges and fine detail. There is no obvious colour cast or colour noise at this stage. There is an apparent increase in ‘graininess’ in the shadow area.
Image 6
The image was exposed for 1/60 second at f/8, ISO setting 1600. There is only a very minor increase in the amount of noise at this ISO setting so after examining the magnified sections of the image I decided to move straight to the next ISO setting.
Image 7
The image was exposed for 1/125 second at f/8, ISO setting 3200.
The picture emerging at this ISO setting is very different. The affect of higher ISO setting on the quality of the image is evident even without any magnification.
On closer examination it becomes apparent that the image quality deteriorated significantly and that the most obvious signs of this deterioration appear in the shadow areas. Additionally, colour specs started to appear in shadow areas and whilst they might not seem too offensive at first sight, they are clearly visible at a higher magnification.
Another observation is that the higher ISO setting seems to affect the colour channels differently. For example, it seems that the green channel in image 7 is affected more that the red channel.
Image 8
The image was exposed for 1/250 second at f/8, ISO setting 6400.
When observing the impact of the change from ISO 3200 to 6400, the most significant effect seems to be in the way that all colour channels are affected. The h red and green channels seem to display clearly visible ‘colour’ specks and graininess. The shadow area clearly displays visible specks of different colours. This also causes the image to look soft and hazy. There is loss of detail, particularly around the edges (for example the leaves and the stem). The highlights are also affected at this ISO setting with a rather ‘washed out’ look. I find this level of noise intolerable.
Image 9
The image was exposed for 1/500 second at f/8, ISO setting 12800. The image shot at ISO 12800 is surprisingly clear when examined without any magnification. However, it is obvious at 1:1 magnification that the level of noise affects the quality of all key areas of this picture.
Image 10
The image was exposed for 1/1000 second at f/8, ISO setting 25600. At ISO 256000, the loss of quality is so significant that it is clearly visible without any magnification. There are large colour specs that distort the colours and affect the sharpness and overall quality of the image.
The damage is particularly obvious in the shadow areas but it is also considerable in light and white areas of the image. In fact, the white background of the image does not seem to be white any more and there are specks of different colours that fill the whole background area. There is considerable loss of detail in shadow areas.
