Imatest Documentation

Imatest Documentation
2 0.173 33.4 2.05 2.78 7.73 0.224 1.14 0.256 15.3 1.93 0.516 0.565
3 0.145 47.5 3.02 3.36 11.3 0.123 1.65 0.216 21.4 2.93 0.402 0.777
4 0.127 62.0 4.02 3.80 14.4 0.071 2.16 0.191 27.4 3.86 0.313 0.99
5 0.115 75.6 4.96 4.18 17.5 0.043 2.65 0.172 33.8 4.98 0.247 1.21
N = number of applications.
m1 = 1/ MTF50 2
Blur more: m2 = (m1-3.6)/14.52
Blur: m3 = (m1-3.6)/6.067
Edge with Blur More applied twice
Unmagnified 4X Magnified
These results confirm an inverse square relationship between MTF50 and the number of Blur More and Blur applications. Two
Blur more operations equals five Blur operations. m2 and m3 are approximately equal to the number of applications.
Each application of Blur More cuts the response
at 0.25 cycles per pixel (half the Nyquist
frequency) by half. This suggests an equation
(though probably not the one used to calculate
BxU): BxU = -log2(MH) = -3.322 * log10(MH),
where MH is the MTF at 0.25 cycles per pixels
(half-Nyquist).
The calculation of variance σ 2 is somewhat tricky. The equation is derived from probability theory, but it can behave strangely.
σ 2 can have negative values because the line spread function LSF(t), which is the derivative of the averaged pulse, can have
negative values (undershoots) that never occur for probability density functions.
First, the mean location of LSF(t) needs to be calculated. This can be done using LSF or LSF 2 . The latter seems to work better.
E(t) = Σ ti LSF 2 (ti) / Σ LSF 2 (ti)
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