数字图像处理matlab版源码V1.1.3(第三章)

由天下分享时间：2025/2/21 15:00:07 加入收藏我要投稿点赞

1、dftfilt

function g = dftfilt(f, H)

?TFILT Performs frequency domain filtering.

% G = DFTFILT(F, H) filters F in the frequency domain using the % filter transfer function H. The output, G, is the filtered

% image, which has the same size as F. DFTFILT automatically pads % F to be the same size as H. Function PADDEDSIZE can be used to % determine an appropriate size for H. %

% DFTFILT assumes that F is real and that H is a real, uncentered % circularly-symmetric filter function.

% Obtain the FFT of the padded input. F = fft2(f, size(H, 1), size(H, 2));

% Perform filtering. g = real(ifft2(H.*F));

% Crop to original size.

g = g(1:size(f, 1), 1:size(f, 2));

2、Dftuv

function [U, V] = dftuv(M, N)

?TUV Computes meshgrid frequency matrices.

% [U, V] = DFTUV(M, N) computes meshgrid frequency matrices U and % V. U and V are useful for computing frequency-domain filter % functions that can be used with DFTFILT. U and V are both % M-by-N.

% Set up range of variables. u = 0:(M - 1); v = 0:(N - 1);

% Compute the indices for use in meshgrid. idx = find(u > M/2); u(idx) = u(idx) - M; idy = find(v > N/2); v(idy) = v(idy) - N;

% Compute the meshgrid arrays.

[V, U] = meshgrid(v, u);

3、hpfilter

function H = hpfilter(type, M, N, D0, n)

%HPFILTER Computes frequency domain highpass filters.

% H = HPFILTER(TYPE, M, N, D0, n) creates the transfer function of % a highpass filter, H, of the specified TYPE and size (M-by-N). % Valid values for TYPE, D0, and n are: %

% 'ideal' Ideal highpass filter with cutoff frequency D0. n % need not be supplied. D0 must be positive. %

% 'btw' Butterworth highpass filter of order n, and cutoff % D0. The default value for n is 1.0. D0 must be % positive. %

% 'gaussian' Gaussian highpass filter with cutoff (standard

% deviation) D0. n need not be supplied. D0 must be % positive.

% The transfer function Hhp of a highpass filter is 1 - Hlp,

% where Hlp is the transfer function of the corresponding lowpass % filter. Thus, we can use function lpfilter to generate highpass % filters.

if nargin == 4

n = 1; % Default value of n. end

% Generate highpass filter. Hlp = lpfilter(type, M, N, D0, n); H = 1 - Hlp;

4、Lpfilter

function H = lpfilter(type, M, N, D0, n)

%LPFILTER Computes frequency domain lowpass filters.

% H = LPFILTER(TYPE, M, N, D0, n) creates the transfer function of % a lowpass filter, H, of the specified TYPE and size (M-by-N). To % view the filter as an image or mesh plot, it should be centered % using H = fftshift(H). %

% Valid values for TYPE, D0, and n are: %

% 'ideal' Ideal lowpass filter with cutoff frequency D0. n need % not be supplied. D0 must be positive.

% 'btw' Butterworth lowpass filter of order n, and cutoff % D0. The default value for n is 1.0. D0 must be % positive. %

% 'gaussian' Gaussian lowpass filter with cutoff (standard

% deviation) D0. n need not be supplied. D0 must be % positive.

% Use function dftuv to set up the meshgrid arrays needed for % computing the required distances. [U, V] = dftuv(M, N);

% Compute the distances D(U, V). D = sqrt(U.^2 + V.^2);

% Begin filter computations. switch type case 'ideal'

H = double(D <= D0); case 'btw'

if nargin == 4 n = 1; end

H = 1./(1 + (D./D0).^(2*n)); case 'gaussian'

H = exp(-(D.^2)./(2*(D0^2))); otherwise

error('Unknown filter type.') end

3、Paddedsize

function PQ = paddedsize(AB, CD, PARAM)

%PADDEDSIZE Computes padded sizes useful for FFT-based filtering. % PQ = PADDEDSIZE(AB), where AB is a two-element size vector, % computes the two-element size vector PQ = 2*AB. %

% PQ = PADDEDSIZE(AB, 'PWR2') computes the vector PQ such that % PQ(1) = PQ(2) = 2^nextpow2(2*m), where m is MAX(AB). %

% PQ = PADDEDSIZE(AB, CD), where AB and CD are two-element size % vectors, computes the two-element size vector PQ. The elements % of PQ are the smallest even integers greater than or equal to % AB + CD - 1. %

% PQ = PADDEDSIZE(AB, CD, 'PWR2') computes the vector PQ such that

% PQ(1) = PQ(2) = 2^nextpow2(2*m), where m is MAX([AB CD]).

if nargin == 1 PQ = 2*AB;

elseif nargin == 2 & ~ischar(CD) PQ = AB + CD - 1; PQ = 2 * ceil(PQ / 2); elseif nargin == 2

m = max(AB); % Maximum dimension.

% Find power-of-2 at least twice m. P = 2^nextpow2(2*m); PQ = [P, P]; elseif nargin == 3

m = max([AB CD]); % Maximum dimension. P = 2^nextpow2(2*m); PQ = [P, P]; else

error('Wrong number of inputs.') end