In order to become independent on the size of the recording medium, all measures are often scaled to the image or picture height (PH). The varying interpretation is now described by ' line widths per mm' or LW/mm. In order to be precise, the test chart line density is now described by ' line pairs per mm' or lp/mm or ' cycles/mm' and means the same as lines per mm. In the digital age this head led to confusion because some people treated the background color as yet another line. Their distance is typically described as ' lines per mm' where mm applies to the recording medium (sensor) rather than the test chart. Many authors use some form of test chart which contain high contrast lines with varying distance. This paper tries to provide a common basis for a quantitative discussion of these aspects. This White Paper is one in a series of articles discussing various aspects in obtaining sharp photographs such as obtaining sharp focus, avoiding shake and motion blur, possible lens resolution etc. 2010/06/lumolabs-understanding-image-sharpness.html#comments

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