Generate an ideal lowpass filter.
gen_lowpass generates an ideal lowpass filter in the frequency domain. The parameter Frequency determines the cutoff frequency of the filter as a fraction of the maximum (horizontal and vertical) frequency that can be represented in an image of size Width x Height, i.e., Frequency should lie between 0 and 1. To achieve a maximum efficiency of the filtering operation, the parameter Norm can be used to specify the normalization factor of the filter. If fft_generic and Norm = 'n' is used the normalization in the FFT can be avoided. Mode can be used to determine where the DC term of the filter lies or whether the filter should be used in the real-valued FFT. If fft_generic is used, 'dc_edge' can be used to gain efficiency. If fft_image and fft_image_inv are used for filtering, Norm = 'none' and Mode = 'dc_center' must be used. If rft_generic is used, Mode = 'rft' must be used. The resulting image has an inner part with the value set to the normalization factor, and an outer part with the value 0.
|
ImageLowpass (output_object) |
image -> object : real |
| Lowpass filter in the frequency domain. | |
|
Frequency (input_control) |
real -> real |
| Cutoff frequency. | |
| Default value: 0.1 | |
| Suggested values: 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 | |
| Restriction: Frequency >= 0 | |
|
Norm (input_control) |
string -> string |
| Normalizing factor of the filter. | |
| Default value: 'none' | |
| List of values: 'none', 'n' | |
|
Mode (input_control) |
string -> string |
| Location of the DC term in the frequency domain. | |
| Default value: 'dc_center' | |
| List of values: 'dc_center', 'dc_edge', 'rft' | |
|
Width (input_control) |
integer -> integer |
| Width of the image (filter). | |
| Default value: 512 | |
| List of values: 128, 160, 192, 256, 320, 384, 512, 640, 768, 1024, 2048, 4096, 8192 | |
|
Height (input_control) |
integer -> integer |
| Height of the image (filter). | |
| Default value: 512 | |
| List of values: 120, 128, 144, 240, 256, 288, 480, 512, 576, 1024, 2048, 4096, 8192 | |
/* Filtering with maximum efficiency with fft_generic. */ gen_lowpass(Lowpass,0.2,'n','dc_edge',Width,Height) fft_generic(Image,ImageFFT,'to_freq',-1,'none','dc_edge','complex') convol_fft(ImageFFT,Lowpass:ImageConvol) fft_generic(ImageConvol,ImageResult,'from_freq',1,'none','dc_edge','byte')
gen_lowpass returns 2 (H_MSG_TRUE) if all parameters are correct. If necessary, an exception handling is raised.
gen_lowpass is reentrant and processed without parallelization.
gen_highpass, gen_bandpass, gen_bandfilter, gen_gauss_filter, gen_derivative_filter
Foundation
