From 676d30b82200f2c538f6fd8006081defa43a6244 Mon Sep 17 00:00:00 2001 From: "Per.Andreas.Brodtkorb" Date: Wed, 23 Nov 2011 16:12:31 +0000 Subject: [PATCH] Added dctn and idctn --- pywafo/src/wafo/dctpack.py | 267 ++++++++++++++++++++++++++++++++++++- 1 file changed, 261 insertions(+), 6 deletions(-) diff --git a/pywafo/src/wafo/dctpack.py b/pywafo/src/wafo/dctpack.py index 3ea245f..de9aa72 100644 --- a/pywafo/src/wafo/dctpack.py +++ b/pywafo/src/wafo/dctpack.py @@ -1,5 +1,5 @@ import numpy as np -__all__ = ['dct', 'idct'] +__all__ = ['dct', 'idct', 'dctn', 'idctn'] def dct(x, n=None): """ Discrete Cosine Transform @@ -54,12 +54,12 @@ def idct(x, n=None): """ Inverse Discrete Cosine Transform - N-1 - x[k] = 1/N sum w[n]*y[n]*cos(pi*k*(2n+1)/(2*N)), 0 <= k < N. - n=0 + N-1 + x[k] = 1/N sum w[n]*y[n]*cos(pi*k*(2n+1)/(2*N)), 0 <= k < N. + n=0 - w(0) = 1/2 - w(n) = 1 for n>0 + w(0) = 1/2 + w(n) = 1 for n>0 Examples -------- @@ -105,3 +105,258 @@ def idct(x, n=None): return y.real else: return y + +def dctn(y, axis=None, w=None): + ''' + DCTN N-D discrete cosine transform. + + Y = DCTN(X) returns the discrete cosine transform of X. The array Y is + the same size as X and contains the discrete cosine transform + coefficients. This transform can be inverted using IDCTN. + + DCTN(X,axis) applies the DCTN operation across the dimension axis. + + Class Support + ------------- + Input array can be numeric or logical. The returned array is of class + double. + + Reference + --------- + Narasimha M. et al, On the computation of the discrete cosine + transform, IEEE Trans Comm, 26, 6, 1978, pp 934-936. + + Example + ------- + RGB = imread('autumn.tif'); + I = rgb2gray(RGB); + J = dctn(I); + imshow(log(abs(J)),[]), colormap(jet), colorbar + + The commands below set values less than magnitude 10 in the DCT matrix + to zero, then reconstruct the image using the inverse DCT. + + J(abs(J)<10) = 0; + K = idctn(J); + figure, imshow(I) + figure, imshow(K,[0 255]) + + See also + -------- + idctn, dct, idct + ''' + + y = np.atleast_1d(y) + shape0 = y.shape + + + if axis is None: + y = y.squeeze() # Working across singleton dimensions is useless + dimy = y.ndim + if dimy==1: + y = np.atleast_2d(y) + y = y.T + # Some modifications are required if Y is a vector +# if isvector(y): +# if y.shape[0]==1: +# if axis==0: +# return y, None +# elif axis==1: +# axis=0 +# y = y.T +# elif axis==1: +# return y, None + + if w is None: + w = [0,] * dimy + for dim in range(dimy): + if axis is not None and dim!=axis: + continue + n = (dimy==1)*y.size + (dimy>1)*shape0[dim] + #w{dim} = exp(1i*(0:n-1)'*pi/2/n); + w[dim] = np.exp(1j * np.arange(n) * np.pi / (2 * n)) + + # --- DCT algorithm --- + if np.iscomplex(y).any(): + y = np.complex(dctn(np.real(y),axis,w),dctn(np.imag(y),axis,w)) + else: + for dim in range(dimy): + y = shiftdim(y,1) + if axis is not None and dim!=axis: + y = shiftdim(y, 1) + continue + siz = y.shape + n = siz[-1] + y = y[...,np.r_[0:n:2, 2*int(n//2)-1:0:-2]] + y = y.reshape((-1,n)) + y = y*np.sqrt(2*n); + y = (np.fft.ifft(y, n=n, axis=1) * w[dim]).real + y[:,0] = y[:,0]/np.sqrt(2) + y = y.reshape(siz) + + #end + #end + + return y.reshape(shape0), w + +def idctn(y, axis=None, w=None): + ''' + IDCTN N-D inverse discrete cosine transform. + X = IDCTN(Y) inverts the N-D DCT transform, returning the original + array if Y was obtained using Y = DCTN(X). + + IDCTN(X,DIM) applies the IDCTN operation across the dimension DIM. + + Class Support + ------------- + Input array can be numeric or logical. The returned array is of class + double. + + Reference + --------- + Narasimha M. et al, On the computation of the discrete cosine + transform, IEEE Trans Comm, 26, 6, 1978, pp 934-936. + + Example + ------- + RGB = imread('autumn.tif'); + I = rgb2gray(RGB); + J = dctn(I); + imshow(log(abs(J)),[]), colormap(jet), colorbar + + The commands below set values less than magnitude 10 in the DCT matrix + to zero, then reconstruct the image using the inverse DCT. + + J(abs(J)<10) = 0; + K = idctn(J); + figure, imshow(I) + figure, imshow(K,[0 255]) + + See also + -------- + dctn, idct, dct + + -- Damien Garcia -- 2009/04, revised 2009/11 + website: www.BiomeCardio.com + + ---------- + [Y,W] = IDCTN(X,DIM,W) uses and returns the weights which are used by + the program. If IDCTN is required for several large arrays of same + size, the weights can be reused to make the algorithm faster. A typical + syntax is the following: + w = []; + for k = 1:10 + [y{k},w] = idctn(x{k},[],w); + end + The weights (w) are calculated during the first call of IDCTN then + reused in the next calls. + ''' + + y = np.atleast_1d(y) + shape0 = y.shape + + if axis is None: + y = y.squeeze() # Working across singleton dimensions is useless + + dimy = y.ndim + if dimy==1: + y = np.atleast_2d(y) + y = y.T + # Some modifications are required if Y is a vector +# if isvector(y): +# if y.shape[0]==1: +# if axis==0: +# return y, None +# elif axis==1: +# axis=0 +# y = y.T +# elif axis==1: +# return y, None +# + + + if w is None: + w = [0,] * dimy + for dim in range(dimy): + if axis is not None and dim!=axis: + continue + n = (dimy==1)*y.size + (dimy>1)*shape0[dim] + #w{dim} = exp(1i*(0:n-1)'*pi/2/n); + w[dim] = np.exp(1j * np.arange(n) * np.pi / (2 * n)) + # --- IDCT algorithm --- + if np.iscomplex(y).any(): + y = np.complex(idctn(np.real(y),axis,w),idctn(np.imag(y),axis,w)) + else: + for dim in range(dimy): + y = shiftdim(y,1) + if axis is not None and dim!=axis: + #y = shiftdim(y, 1) + continue + siz = y.shape + n = siz[-1] + + y = y.reshape((-1,n)) * w[dim] + y[:,0] = y[:,0]/np.sqrt(2) + y = (np.fft.ifft(y, n=n, axis=1)).real + y = y * np.sqrt(2*n) + + I = np.empty(n,dtype=int) + I.put(np.r_[0:n:2],np.r_[0:int(n//2)+np.remainder(n,2)]) + I.put(np.r_[1:n:2],np.r_[n-1:int(n//2)-1:-1]) + y = y[:,I] + + y = y.reshape(siz) + + + y = y.reshape(shape0); + return y, w + + + +def no_leading_ones(x): + first = 0 + for i, xi in enumerate(x): + if xi != 1: + first = i + break + return x[first:] + +def shiftdim(x, n=None): + if n is None: + # returns the array B with the same number of + # elements as X but with any leading singleton + # dimensions removed. + return x.reshape(no_leading_ones(x.shape)) + elif n>=0: + # When n is positive, shiftdim shifts the dimensions + # to the left and wraps the n leading dimensions to the end. + return x.transpose(np.roll(range(x.ndim), -n)) + else: + # When n is negative, shiftdim shifts the dimensions + # to the right and pads with singletons. + return x.reshape((1,)*-n+x.shape) + +def test_dctn(): + a = np.arange(12).reshape((3,-1)) + #y = dct(a) + #x = idct(y) + #print(y) + #print(x) + + print(a) + yn = dctn(a)[0] + xn = idctn(yn)[0] + + print(yn) + print(xn) + + + +def test_docstrings(): + import doctest + doctest.testmod() + +if __name__ == '__main__': + #test_docstrings() + test_dctn() \ No newline at end of file