# Name

filt_tophatl - top-hat low-pass Fourier filter (truncation of a Fourier series)

# Usage

output = filt_tophatl(image, freq, pad)

## Input

- image
- input image (can be either real or Fourier)
- freq
- stop-band frequency
- pad
- logical flag specifying whether before filtering the image should be padded with zeroes in real space to twice the size (this helps avoiding aliasing artifacts). (Default pad = False).

All frequencies are in absolute frequency units

``f_a``and their valid range is [0:0.5].

## Output

- output
- filtered image. Output image is real when input image is real or Fourier when input image is Fourier

# Method

Fourier transform of the input image is set to zero for spatial frequencies larger than freq.

# Reference

Gonzalez, R. F., Woods, R. E., 2002. Digital Image Processing. Prentice Hall, Upper Saddle River, NJ.

# Author / Maintainer

Pawel A. Penczek

# Keywords

- category 1
- FILTER
- category 2
- FOURIER

# Files

filter.py

# Maturity

- stable
- works for most people, has been tested; test cases/examples available.

# Bugs

None. It is perfect.