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--- definitions:absolute_frequency_units [2016/12/12 17:07]
fmerino [Definition]
+++ definitions:absolute_frequency_units [2016/12/14 10:37]
fmerino
@@ Line 2: / Line 2: @@
 ==== Definitions ====
-Inside SPHIRE, we define the spatial frequencies are handled in absolute units. This means that the spatial frequencies are expressed in term of pixels units, or absolute frequency $f_a$, instead of units of inverse distance. In this way $f_a=0$ corresponds to the zero Fourier term (zero frequency), while $f_a=0.5$  corresponds to Nyquist frequency $f_N$. The Nyquist frequency corresponds the maximum spatial frequency contained in an image. In absolute frequencies this always has a value of 0.5 while in inverse distance it will correspond to $f_N=\frac{1}{2p}$, where $p$ is the pixel size usually in Å.
+Inside SPHIRE, spatial frequencies are handled in absolute units. This means that the spatial frequencies are expressed in term of pixels, or absolute frequency $f_a$, instead of units of inverse distance. The Nyquist frequency, the maximum spatial frequency contained in an image, corresponds to $f_a=0.5$. In inverse distance units, it will correspond to $f_N=\frac{1}{2p}$, where $p$ is the pixel size, usually in Å.
-A simple relation exists between spatial frequencies $f_s$ and absolute frequencies $f_a$:
+A simple relation exists between spatial frequencies $f_s$ (e.g. $\frac{1}{\text{\AA}}$) and absolute frequencies $f_a$:
-For an image with pixel size $p$ [Å] by:
+For an image with pixel size $p$ by:
 $$
 f_s=\frac{f_a}{p}

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