**PURPOSE**- Computes the self-correlation function of an image/volume byusing the Fourier transform relationship. Example.

**SEE ALSO****AC N**[Auto Correlation - Normalized ||] **AC NS**[Self Correlation - Normalized ||] **AC MS**[Auto Correlation - Masked and normalized ||] **CC**[Cross Correlation ||] **CC N**[Cross Correlation - Normalized ||] **CN**[Convolution ||] **CN N**[Convolution - Normalized ||] **FT**[Fourier Transform ||]

**USAGE**- .OPERATION: AC S

- .INPUT FILE: PIC001

[Enter the name of the picture to be self-correlated.].OUTPUT FILE: ACF001

[Enter name of the file which will contain the self-correlation coefficients.]

**NOTES**

- On completion of this operation, the output file will contain
the self-correlation function. The origin is at
(INT(NX/2) + 1, INT(NY/2) + 1, INT(NZ/2) + 1).
The SCF is not normalized.
- The type of input data can be either real or Fourier.
- The self-correlation function is defined in "Correlation functions revisited", M. van Heel, M. Schatz, E. Orlova. Ultramicroscopy, 46, (1992) 307-316; as inverse Fourier transform of the modulus of the Fourier transform of the input image.

**SUBROUTINES**- ACRS_3S

**CALLER**- CORR1

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