Saturday, 22 May 2010

Digital Photographic Practice: Exercise 5: Sensor Linear Capture

I chose this image of Reykjavik for this exercise as it had a fairly full range if tones and a number of flat neutral areas – although with hindsight it would probably be better to have an image with more dark tones.
The ‘linear’ version of this loses virtually all detail in the relatively dark foreground as predicted by the exercise text. Interestingly, but not directly relevant to this exercise, there was a slight colour shift on screen as I converted it using ‘save for web’ in Elements.
As I have a relatively old version of Elements I re-corrected the TIFF image in Lightroom to give this very slightly  lighter version of the original. I struggled to get any closer  to the original but inspection of the image confirms the exercise – there is extra noise generated by this process.
Here are clips of the base of the church tower before (RHS) and after (LHS) processing. In spite of the limitations of the jpeg compression there is an increase in noise visible. At this scale and compression it manifests itself as a smoother look to the concrete in the LH image – there is also less detail visible in the tree. These effects are much more noticeable magnified in an image editing package.
Reykjavik-Clip  Reykjavik-Corrected-clip
The implication of this for image quality are clear. If we need to brighten the shadows significantly for underexposure the cost is an increase in visible noise, and a degradation of image quality.

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