Compute lambdas for channel power law scaling. For a broad family of features, including gradient histograms and all channel types tested, the feature responses computed at a single scale can be used to approximate feature responses at nearby scales. The approximation is accurate at least within an entire scale octave. For details and to understand why this unexpected result holds, please see: P. Dollár, R. Appel, S. Belongie and P. Perona "Fast Feature Pyramids for Object Detection", PAMI 2014. This function computes channels at multiple image scales and plots the resulting power law scaling. The purpose of this function is two-fold: (1) compute lambdas for fast approximate channel computation for use in chnsPyramid() and (2) provide a visualization of the power law channel scaling described in the BMVC2010 paper. chnsScaling() takes two main inputs: the parameters for computing image channels (pChns), and an image or set of images (Is). The images are cropped to the dimension of the smallest image for simplicity of computing the lambdas (and fairly high resolution images are best). The computed lambdas will depend on the channel parameters (e.g. how much smoothing is performed), but given enough images (>1000) the computed lambdas should not depend on the exact images used. USAGE [lambdas,as,scales,fs] = chnsScaling( pChns, Is, [show] ) INPUTS pChns - parameters for creating channels (see chnsCompute.m) Is - [nImages x 1] cell array of images (nImages may be 1) show - [1] figure in which to display results OUTPUTS lambdas - [nTypes x 1] computed lambdas as - [nTypes x 1] computed y-intercepts scales - [nScales x 1] vector of actual scales used fs - [nImages x nScales x nTypes] array of feature means EXAMPLE sDir = 'data/Inria/train/neg/'; Is = fevalImages( @(x) {x}, {}, sDir, 'I', 'png', 0, 200 ); p = chnsCompute(); lambdas = chnsScaling( p, Is, 1 ); See also chnsCompute, chnsPyramid, fevalImages Piotr's Computer Vision Matlab Toolbox Version 3.25 Copyright 2014 Piotr Dollar & Ron Appel. [pdollar-at-gmail.com] Licensed under the Simplified BSD License [see external/bsd.txt]

Generated by