如何填充从浅黄色到深黄色的渐变色？

Question

用matlab，我不知道patch如何在这张图片中垂直制作渐变色。在这里，我只想要一个简单的颜色渐变。我已经使用 bwboundaries 来捕捉边缘函数并填充纯色，就像这样：

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 在他对您的其他问题的回答中：

  %% 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'); 

如果你正确理解了代码，你将能够做到垂直渐变。我不小心做了水平，但应该没问题。代码已注释，但请不要犹豫。步骤如下

• 根据需要创建随机颜色。在这种情况下 2
• 转换为HSV
• 创建一系列V 值，代表“光”
• 为图像上的每一行重复该颜色列表
• 用标签掩盖它，只是将它添加到该标签的区域