**PURPOSE**- Calculates autocorrelation coefficients for circular mask. Coefficients are normalized. Image is padded with zeros. Works only for real images (not their Fourier transforms!). Example.

**USAGE**- .OPERATION: AC MS

- .INPUT FILE: PIC001

[Enter the name of the file to be autocorrelated.].OUTPUT FILE: MAC001

[Enter name of the file which will contain AC coeffs.].MASK RADIUS: 25

[Enter radius of the circular mask which will be centered at NX/2+1, NY/2+1].(F)ULL OR (H)ALF OUTPUT FILE: F

[*F*results in a autocorrelation function file with dimensions 2*NX,2*NY (useful for mask radius =>MAX(NX/4,NY/4).

*H*results in a autocorrelation function file with dimensions NX, NY (enough if one is interested only in lower order ACF coeffs. or mask radius is small)]

**NOTES**

- On completion of this operation, the output file will contain
the auto-correlation function. The origin is at
(NX/2 + 1, NY/2 + 1). The ACF is not normalized.
- For non-masked autocorrelation function use 'AC'.
- Implemented by Paul Penczek.

**SUBROUTINES**- MACF, MACF_P, FMRS_2, FMRS_1, FFTMCF, ACRS_2

**CALLER**- CORR1

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