Sunday, 12 May 2013

My (fairly high) tolerance for noise

I was curious to see practically how much tolerance for noise in a telling situation (such as the one suggested in the course described) would be within such a photograph. The reason for this was that previously I had veered from being very picky about any noise to being extremely tolerant for noise, without commencing upon a strategic test like this.

   My first impressions when looking at 'Grey Texture' was that there was a lot of noise. However, upon closer inspection I saw there was also a lot of detail. As well as this the image was a zoomed part of a larger photograph and yet appeared mostly 'natural' to my eyes, where the zoomed in part of the photograph still remained true to life. In particular the brighter areas of the grey fabric possessed this attribute, where (barely perceivable) detail - vertical ribbing and mottling were present. The mottling especially I mistook as noise because it looked less natural. The shadow areas held up less well.

   For me when looking at the crops of 'Turkish Dance', the most 'important' areas of the image like the faces and the silver brocades consisted of less noise than the shadow areas, which coincidentally happened to contain 'less-important' areas. I felt this was because those 'important' areas were well-exposed. I decided to investigate whether this inkling was true and found a statement that said: 'images which are underexposed will have more visible noise — even if you brighten them up to a more natural level afterwards' - Cambridge in Colour (2013). This interested me because it therefore followed that shadow areas within a photograph (which would count as underexposed areas in a typical exposure) would contain more noise than the well-exposed parts. This confirmed my inkling and I therefore predicted my tolerance for noise would be higher in non-shadow areas. I also felt that this statement had an important implication concerning how I approached digital noise in my photographs in the future. The implication was provided I exposed a photograph 'correctly' during capture, there would be less noise, particularly in well-exposed areas.

Figure 1 - the range of my camera's ISO values - a 100% crop including textureless shadow
Figure 2 - the range of my camera's ISO values - a 100% crop including an area of sharp detail
   To test out myself whether shadow areas contained more noise than well-lit areas, along with any other observations, I set up the suggested scene and started to compare the resulting images at different sizes of magnification. The first (and for me the most important) comparison was to look at the images on my computer monitor at a size that fitted the screen and then also at print size. I found the images to be perfectly acceptable at ISOs up to and including ISO 6400 on my camera for the aforementioned sizes. There was however some noticeable loss in colour richness at ISO 6400 and higher. Beyond ISO 6400 (up to ISO 16000) on my camera, even at the print size magnification, noise became too pronounced for me, especially in the shadow areas. Expectedly, zooming in further (I went straight to 100% magnification), made the noise become very obtrusive at ISOs 16000 and 12800 and only became minimal at ISO 800.

Photograph 1 - The scene I chose to conduct the test (this image at ISO 3200)
   I would say crucially however, that the highest ISO value in this test scene that acceptably balanced detail with noise at 100% magnification and print size magnification was ISO 3200 for my camera. I based this statement on the textureless area in shadow appearing natural at print size magnification - there was a lot less noise in the well-lit areas of the photograph as predicted. Also I based this assertion on my perception that the area of sharp detail (the jewellery on the subject's neck) remained perceivable as detail and not noise at 100% magnification at this ISO value. Lastly, the colours stayed rich at this ISO value.

   So overall I discovered that, for myself, as long as the noise didn't detract conspicuously from the impact of one of my photographs at print size or lesser, I was quite happy to let non-obtrusive noise in. This was provided I got the framing close to being 'right' (thus negating the need to crop, which would probably make any noise more apparent). This was probably because the sensor resolved more detail (in my eyes) than was perceivable at first glance. This meant the ISO value range for most of my photographs was large and therefore malleable for different situations. Finally, I learnt exposure was key, as well as low ISOs in reducing noise in images (especially shadow areas).

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