how to fill gradient color from light yellow to dark yellow? - matlab

Question

With matlab, I don't know how patch can make gradient color vertically in this picture. Here I just want a simple color gradient. I have used bwboundaries to catch the edge function and fill pure color just like this:
for i=1:4
input=imread(['heartspline2_4_',num2str(i)],'bmp');
figure,imshow(input);
BW=im2bw(input,graythresh(input));
[B,L]=bwboundaries(BW,'noholes');
for k=1:length(B)
boundary=B{k};
plot(boundary(:,2),boundary(:,1),'k','LineWidth',2);
fvc=[1 1 0;1 0 0;0 0 1];
hold on;
axis off;
if (k==1)
patch(boundary(:,2),boundary(:,1),'w');
else
p=patch(boundary(:,2),boundary(:,1),'y');
end
end
saveas(gca,['y_','heartspline2_4_',num2str(i)],'bmp')
close(gcf)
end

Answer 1

Following Shai's code in his answer in your other question:
%% Load image %%
close all; clear all; clc;
img = imread('https://i.stack.imgur.com/yO8Nd.jpg'); %// read image
bw = img(:,:,1) > 128; %// convert to binary mask
lb = bwlabel(bw,4); %// extract distinct regions
%%
%% Create as many colors as needed
% example: 2
cmap=rand(2,3); % make this yellow if needed
% lets convert to HSV, we can tune the intesity of the image better here
cmap=rgb2hsv(cmap);
% for each color, lets crate a set of colors.
for ii=1:size(cmap,1);
colors{ii}= [cmap(ii,1)*ones(1,size(img,2)); cmap(ii,2)*ones(1,size(img,2)); linspace(0.3,1,size(img,2))].';
% Modify the limits of linspace
% to achieve control over the limits
end
% Now we have the colors, lets create an image of vertical colors and mask
% it
cimage=zeros(size(img,1),size(img,2),3); % empthy color image
finalimage=cimage;
for ii=1:size(colors,2)
colors{ii}=hsv2rgb(colors{ii});
cimage=permute(reshape(repmat(colors{ii},[size(img,1),1,1]),[size(img,2),size(img,1),3]),[2,1,3]); % there is probably a simpler way
finalimage=finalimage+cimage.*repmat((lb==ii),[1 1 3]);
end
figure; imshow(finalimage, [], 'border', 'tight');
If you understand the code properly, you will be able to do it for vertical gradient. I accidentally did horizontal, but should be alright. The code is commented, but do not hesitate to ask. The steps are the following
Create random colors, as many as desired. In this case 2
convert to HSV
Create a range of V values, that represent "light"
Repeat that list of colors for every row on the image
mask it with the labels to just add it to the areas of that label