Module code >> skvideo.measure.strred
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Source code for skvideo.measure.strred

from ..utils import *
import numpy as np
import scipy.ndimage
import scipy.linalg

def est_params(frame, blk, sigma_nn):
    h, w = frame.shape
    sizeim = np.floor(np.array(frame.shape)/blk) * blk
    sizeim = sizeim.astype(

    frame = frame[:sizeim[0], :sizeim[1]]

    temp = []
    for u in range(blk):
      for v in range(blk):
        temp.append(np.ravel(frame[v:(sizeim[0]-(blk-v)+1), u:(sizeim[1]-(blk-u)+1)]))
    temp = np.array(temp).astype(np.float32)

    cov_mat = np.cov(temp, bias=1).astype(np.float32)

    # force PSD
    eigval, eigvec = np.linalg.eig(cov_mat)
    Q = np.matrix(eigvec)
    xdiag = np.matrix(np.diag(np.maximum(eigval, 0)))
    cov_mat = Q*xdiag*Q.T

    temp = []
    for u in range(blk):
      for v in range(blk):
        temp.append(np.ravel(frame[v::blk, u::blk]))
    temp = np.array(temp).astype(np.float32)

    # float32 vs float64 difference between python2 and python3 
    # avoiding this problem with quick cast to float64
    V,d = scipy.linalg.eigh(cov_mat.astype(np.float64))
    V = V.astype(np.float32)

    # Estimate local variance
    sizeim_reduced = (sizeim/blk).astype(
    ss = np.zeros((sizeim_reduced[0], sizeim_reduced[1]), dtype=np.float32)
    if np.max(V) > 0:
      # avoid the matrix inverse for extra speed/accuracy
      ss = scipy.linalg.solve(cov_mat, temp)
      ss = np.sum(np.multiply(ss, temp) / (blk**2), axis=0)
      ss = ss.reshape(sizeim_reduced)

    V = V[V>0]

    # Compute entropy
    ent = np.zeros_like(ss, dtype=np.float32)
    for u in range(V.shape[0]):
      ent += np.log2(ss * V[u] + sigma_nn) + np.log(2*np.pi*np.exp(1))

    return ss, ent

def extract_info(frame1, frame2):
    blk = 3
    sigma_nsq = 0.1
    sigma_nsqt = 0.1

    model = SpatialSteerablePyramid(height=6)
    y1 = model.extractSingleBand(frame1, filtfile="sp5Filters", band=0, level=4)
    y2 = model.extractSingleBand(frame2, filtfile="sp5Filters", band=0, level=4)

    ydiff = y1 - y2

    ss, q = est_params(y1, blk, sigma_nsq)
    ssdiff, qdiff = est_params(ydiff, blk, sigma_nsqt)

    spatial = np.multiply(q, np.log2(1 + ss))
    temporal = np.multiply(qdiff, np.multiply(np.log2(1 + ss), np.log2(1 + ssdiff)))

    return spatial, temporal

[docs]def strred(referenceVideoData, distortedVideoData): """Computes Spatio-Temporal Reduced Reference Entropic Differencing (ST-RRED) Index. [#f1]_ Both video inputs are compared over frame differences, with quality determined by differences in the entropy per subband. Parameters ---------- referenceVideoData : ndarray Reference video, ndarray of dimension (T, M, N, C), (T, M, N), (M, N, C), or (M, N), where T is the number of frames, M is the height, N is width, and C is number of channels. Here C is only allowed to be 1. distortedVideoData : ndarray Distorted video, ndarray of dimension (T, M, N, C), (T, M, N), (M, N, C), or (M, N), where T is the number of frames, M is the height, N is width, and C is number of channels. Here C is only allowed to be 1. Returns ------- strred_array : ndarray The ST-RRED results, ndarray of dimension ((T-1)/2, 4), where T is the number of frames. Each row holds spatial score, temporal score, reduced reference spatial score, and reduced reference temporal score. strred : float The final ST-RRED score if all blocks are averaged after comparing reference and distorted data. This is close to full-reference. strredssn : float The final ST-RRED score if all blocks are averaged before comparing reference and distorted data. This is the reduced reference score. References ---------- .. [#f1] R. Soundararajan and A. C. Bovik, "Video Quality Assessment by Reduced Reference Spatio-temporal Entropic Differencing," IEEE Transactions on Circuits and Systems for Video Technology, April 2013. """ referenceVideoData = vshape(referenceVideoData) distortedVideoData = vshape(distortedVideoData) assert(referenceVideoData.shape == distortedVideoData.shape) T, M, N, C = referenceVideoData.shape assert C == 1, "strred called with videos containing %d channels. Please supply only the luminance channel" % (C,) referenceVideoData = referenceVideoData[:, :, :, 0] distortedVideoData = distortedVideoData[:, :, :, 0] rreds = [] rredt = [] rredssn = [] rredtsn = [] for i in range(0, T-1, 2): refFrame1 = referenceVideoData[i].astype(np.float32) refFrame2 = referenceVideoData[i+1].astype(np.float32) disFrame1 = distortedVideoData[i].astype(np.float32) disFrame2 = distortedVideoData[i+1].astype(np.float32) spatialRef, temporalRef = extract_info(refFrame1, refFrame2) spatialDis, temporalDis = extract_info(disFrame1, disFrame2) rreds.append(np.mean(np.abs(spatialRef - spatialDis))) rredt.append(np.mean(np.abs(temporalRef - temporalDis))) rredssn.append(np.abs(np.mean(spatialRef - spatialDis))) rredtsn.append(np.abs(np.mean(temporalRef - temporalDis))) rreds = np.array(rreds) rredt = np.array(rredt) rredssn = np.array(rredssn) rredtsn = np.array(rredtsn) srred = np.mean(rreds) trred = np.mean(rredt) srredsn = np.mean(rredssn) trredsn = np.mean(rredtsn) strred = srred * trred strredsn = srredsn * trredsn return np.hstack((rreds.reshape(-1, 1), rredt.reshape(-1, 1), rredssn.reshape(-1, 1), rredtsn.reshape(-1, 1))), strred, strredsn