Convert RGB image to other color spaces (highly optimized). If colorSpace=='gray' transforms I to grayscale. The output is within numerical error of Matlab's rgb2gray, except ~10x faster. The output in this case is hxwx1, and while the input must be hxwx3 for all other cases, the input for this case can also be hxwx1 (normalization only). If colorSpace=='hsv' transforms I to the HSV color space. The output is within numerical error of Matlab's rgb2hsv, except ~15x faster. If colorSpace=='rgb' or colorSpace='orig' only normalizes I to be in the range [0,1]. In this case both the input and output may have an arbitrary number of channels (that is I may be [hxwxd] for any d). If colorSpace=='luv' transforms I to the LUV color space. The LUV color space is "perceptually uniform" (meaning that two colors equally distant in the color space according to the Euclidean metric are equally distant perceptually). The L,u,v channels correspond roughly to luminance, green-red, blue-yellow. For more information see: http://en.wikipedia.org/wiki/CIELUV - using this color spaces http://en.wikipedia.org/wiki/CIELAB - more info about color spaces The LUV channels are normalized to fall in ~[0,1]. Without normalization the ranges are L~[0,100], u~[-88,182], and v~[-134,105] (and typically u,v~[-100,100]). The applied transformation is L=L/270, u=(u+88)/270, and v=(v+134)/270. This results in ranges L~[0,.37], u~[0,1], and v~[0,.89]. Perceptual uniformity is maintained since divisor is constant (normalizing each color channel independently would break uniformity). To undo the normalization on an LUV image J use: J=J*270; J(:,:,2)=J(:,:,2)-88; J(:,:,3)=J(:,:,3)-134; To test the range of the colorSpace use: R=100; I=zeros(R^3,1,3); k=1; R=linspace(0,1,R); for r=R, for g=R, for b=R, I(k,1,:)=[r g b]; k=k+1; end; end; end J=rgbConvert(I,'luv'); [min(J), max(J)] This code requires SSE2 to compile and run (most modern Intel and AMD processors support SSE2). Please see: http://en.wikipedia.org/wiki/SSE2. USAGE J = rgbConvert( I, colorSpace, [useSingle] ); INPUTS I - [hxwx3] input rgb image (uint8 or single/double in [0,1]) colorSpace - ['luv'] other choices include: 'gray', 'hsv', 'rgb', 'orig' useSingle - [true] determines output type (faster if useSingle) OUTPUTS J - [hxwx3] single or double output image (normalized to [0,1]) EXAMPLE - luv I = imread('peppers.png'); tic, J = rgbConvert( I, 'luv' ); toc figure(1); montage2( J ); EXAMPLE - hsv I=imread('peppers.png'); tic, J1=rgb2hsv( I ); toc tic, J2=rgbConvert( I, 'hsv' ); toc mean2(abs(J1-J2)) EXAMPLE - gray I=imread('peppers.png'); tic, J1=rgb2gray( I ); toc tic, J2=rgbConvert( I, 'gray' ); toc J1=single(J1)/255; mean2(abs(J1-J2)) See also rgb2hsv, rgb2gray Piotr's Computer Vision Matlab Toolbox Version 3.02 Copyright 2014 Piotr Dollar & Ron Appel. [pdollar-at-gmail.com] Licensed under the Simplified BSD License [see external/bsd.txt]

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