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I am having a issue with a question with regards to how spatial frequency and high contrast are related.

Explain how high contrast resolution of an imaging system may be expressed in terms of a spatial frequency, measured in units of line pairs per mm.

As I understand spatial frequency is the amount of line pairs that occur with in a given distance, and by line pairs I mean a pair of black and white lines, so one line pair would be one black line and one white line.

If I think of a normal photo being taken the the higher the spatial frequency the more detailed the image is, but how does the increased spatial frequency effect the contrast of the image?

I can only thing that this would have to do with the thickness of the black and white lines.

For example say I take and x-ray image and there is a high contrast with in that image i.e a calcification, then to show in detail the difference in contrast I assume that the white line would be slight thicker than the black, so the more line per mm would give and brighter more white look I.e high contrast than say compared to the surrounding tissue in which, the line would be more a thicker black than white, to give a greyer kind on tone.

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  • $\begingroup$ Why was I down voted? $\endgroup$ – james2018 Aug 6 '18 at 9:24
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The term "high contrast" this context refers to the type of pattern used to measure the resolution of the imaging system. For example, a resolution pattern etched in lead foil would be a test object used to measure high contrast resolution. The line pairs are designed to have high contrast between them. The test pattern is designed to evaluate how the imaging system reproduces or transfers high contrast differences.

There are also low contrast resolution test objects, which typically contain disks of material that have low contrast compared to the surrounding.

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An imaging system will spatially spread a point or line object. This will translate resolution to contrast as can be seen in the picture.resolution to contrast mapping

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