function [VG, A, PPG] = colorgrad(f, T)

if (ndims(f)~=) || (size(f,)~=)

    error('Input image must be RGB');

end

sh = fspecial('sobel');

sv = sh';

Rx = imfilter(double(f(:,:,)), sh, 'replicate');

Ry = imfilter(double(f(:,:,)), sv, 'replicate');

Gx = imfilter(double(f(:,:,)), sh, 'replicate');

Gy = imfilter(double(f(:,:,)), sv, 'replicate');

Bx = imfilter(double(f(:,:,)), sh, 'replicate');

By = imfilter(double(f(:,:,)), sv, 'replicate');

gxx = Rx.^ + Gx.^ + Bx.^;

gyy = Ry.^ + Gy.^ + By.^;

gxy = Rx.*Ry + Gx.*Gy + Bx.*By;

A = 0.5*(atan(*gxy./(gxx-gyy+eps)));

G1 = 0.5*((gxx+gyy) + (gxx-gyy).*cos(*A) + *gxy.*sin(*A));

A = A + pi/;

G2 = 0.5*((gxx+gyy) + (gxx-gyy).*cos(*A) + *gxy.*sin(*A));

G1 = G1.^0.5;

G2 = G2.^0.5;

VG = mat2gray(max(G1, G2));

RG = sqrt(Rx.^ + Ry.^);

GG = sqrt(Gx.^ + Gy.^);

BG = sqrt(Bx.^ + By.^);

PPG = mat2gray(RG + GG + BG);

if nargin ==

    VG = (VG>T).*VG;

    PPG = (PPG>T).*PPG;

end

close all;clear all;clc;

f = imread('wo.jpg');

[VG,A,PPG] = colorgrad(f);

ppg = im2uint8(PPG);

ppgf =  - ppg;

[M,N] = size(ppgf);

T=;

ppgf1 = zeros(M,N);

for ii = :M

    for jj = :N

        if ppgf(ii,jj)<T %边缘区域

%             ppgf1(ii,jj)=;

            ppgf1(ii,jj)=(T-ppgf1(ii,jj))/;

        else %平滑区域

            ppgf1(ii,jj)=/(-T)*(ppgf(ii,jj)-T);

        end

    end

end

ppgf1 = uint8(ppgf1);

figure;

subplot();imshow(ppgf);

subplot();imshow(ppgf1);

subplot();imhist(ppgf);

subplot();imhist(ppgf1);

figure;imshow(ppgf1);