Color-pass filter by Hue - matlab

Question

Why doesn't color filter below find green peppers?
The code:
function [ outhsv ] = ColorFilter( hsv, h, s )
%COLORFILTER Summary of this function goes here
% Detailed explanation goes here
if nargin < 2
h = [];
end
if nargin < 3
s = [];
end
if size(h,2)==1
h = padarray(h, [0 1], 1/100, 'post');
end
if size(s,2)==1
s = padarray(s, [0 1], 1/100, 'post');
end
if isempty(h)
v_of_h = ones(size(hsv,1), size(hsv,2));
else
v_of_h = WeightFunction( hsv(:,:,1), h(:,1), h(:,2));
end
if isempty(s)
v_of_s = ones(size(hsv,1), size(hsv,2));
else
v_of_s = WeightFunctionOnce( hsv(:,:,2), s(:,1), s(:,2));
end
outhsv = hsv;
outhsv(:,:,3) = hsv(:,:,3) .* v_of_h .* v_of_s;
function y = WeightFunction( x, mu, sigma )
%y = WeightFunctionOnce(x,mu,sigma) + WeightFunctionOnce(x-1,mu,sigma);
y = 1 - (1-WeightFunctionOnce(x,mu,sigma)) .* (1-WeightFunctionOnce(x-1,mu,sigma));
function y = WeightFunctionOnce( x, mu, sigma )
if nargin<2
mu=0;
elseif nargin<3
sigma=1./100.;
end
if any(size(mu) ~= size(sigma))
error('mu and sigma should be of the same size');
end
y = zeros([size(x) numel(mu)]);
for i=1:numel(mu)
y(:,:,i) = exp(-((x - mu(i)) .^ 2 ./ (2 .* sigma(i) .^ 2)));
end
%y = sum(y,3)/size(y,3);
y = 1-prod(1-y,3);
Display code:
hue = 120;
h = [hue/360 0.05];
s = [];
rgb1 = imread('huescale.png');
%rgb1 = imread('peppers.png');
hsv1 = rgb2hsv(rgb1);
hsv2 = ColorFilter(hsv1, h, s);
rgb2 = hsv2rgb(hsv2);
bitmask = hsv1(:,:,1)>(h(1)-h(2)) & hsv1(:,:,1)<(h(1)+h(2));
figure;
subplot(3,1,1); imshow(rgb1);
subplot(3,1,2); imshow(rgb2);
subplot(3,1,3); imshow(bitmask);
result on scale
(works)
result on peppers:
(does not)
Why?

Answer 1

If you looked closer at the H values, those green peppers are kind of yellowish, so you might want to widen the rule a bit.
I would suggest something in between 0.15 and 0.5. You can also combine with saturation channel, say only consider portions of images that are vibrant, i.e., we want to get rid of the onions. Try the following codes to get a preview.
hsv_dat = rgb2hsv(imread('peppers.png'));
imagesc(hsv_dat(:,:,1) > 0.15 & hsv_dat(:,:,1) < 0.5 & hsv_dat(:,:,2) > 0.3)
colormap(gray)
You should get