如何在 MATLAB 中创建带有线条的图像矩阵? [英] How do I create an image matrix with a line drawn in it in MATLAB?

问题描述

我想绘制一条从一个明确定义的点到另一个点的线，然后将其转换为图像矩阵以在其上使用高斯滤波器进行平滑.为此，我使用函数 line 和 getframe 来绘制一条线并捕获图像中的图形窗口，但是 getframe 非常慢，而且不非常可靠.我注意到当计算机锁定时它不会捕获任何内容，并且在执行 170 次后出现 内存不足 错误.

我的问题是:

• 我可以使用 getframe 的替代品吗?
• 有没有办法创建图像矩阵并直接在其中画线?

这是一个最小的代码示例:

figure1=line([30 35] ,[200 60]);F=获取帧；hsize=40;西格玛=20；h = fspecial('gaussian',hsize,sigma);FilteredImg = imfilter(double(F.cdata), h,256);imshow(uint8(filteredImg));

[更新]

High-Performance Mark 使用linspace 的想法看起来很有前途，但我如何访问使用linspace 计算的矩阵坐标?我尝试了以下代码，但它没有像我认为的那样工作.我认为这是一个非常简单和基本的 MATLAB 东西，但我无法理解它:

matrix=zeros(200,60);对角线=圆形([linspace(30,200，numSteps)；linspace(35,60，numSteps)])；矩阵(对角线(1，:)，对角线(2，:))=1；imshow(矩阵)；

解决方案

这是一个直接在矩阵中绘制直线的示例.首先，我们将为空图像创建一个零矩阵:

mat = zeros(250, 250, 'uint8');% uint8 类型的 250×250 矩阵

然后，假设我们要绘制一条从 (30, 35) 到 (200, 60) 的线.我们将首先计算这条线必须有多少像素长:

x = [30 200];% x 坐标(沿矩阵列运行)y = [35 60];% y 坐标(沿矩阵行运行)nPoints = max(abs(diff(x)), abs(diff(y)))+1;% 直线上的点数

接下来，我们使用

I want to plot a line from one well-defined point to another and then turn it into an image matrix to use a Gaussian filter on it for smoothing. For this I use the functions line and getframe to plot a line and capture the figure window in an image, but getframe is very slow and not very reliable. I noticed that it does not capture anything when the computer is locked and I got an out of memory error after 170 executions.

My questions are:

• Is there a substitute to getframe that I can use?
• Is there a way to create the image matrix and draw the line directly in it?

Here is a minimal code sample:

figure1=line([30 35] ,[200 60]);
F= getframe;
hsize=40; sigma=20;
h = fspecial('gaussian',hsize,sigma); 
filteredImg = imfilter(double(F.cdata), h,256);
imshow(uint8(filteredImg));

[update]

High-Performance Mark's idea with linspace looks very promising, but how do I access the matrix coordinates calculated with linspace? I tried the following code, but it does not work as I think it should. I assume it is a very simple and basic MATLAB thing, but I just can not wrap my head around it:

matrix=zeros(200,60);
diagonal=round([linspace(30,200,numSteps); linspace(35,60,numSteps)]);
matrix(diagonal(1,:), diagonal(2,:))=1;
imshow(matrix);

解决方案

Here's one example of drawing a line directly into a matrix. First, we'll create a matrix of zeros for an empty image:

mat = zeros(250, 250, 'uint8');  % A 250-by-250 matrix of type uint8

Then, let's say we want to draw a line running from (30, 35) to (200, 60). We'll first compute how many pixels long the line will have to be:

x = [30 200];  % x coordinates (running along matrix columns)
y = [35 60];   % y coordinates (running along matrix rows)
nPoints = max(abs(diff(x)), abs(diff(y)))+1;  % Number of points in line

Next, we compute row and column indices for the line pixels using linspace, convert them from subscripted indices to linear indices using sub2ind, then use them to modify mat:

rIndex = round(linspace(y(1), y(2), nPoints));  % Row indices
cIndex = round(linspace(x(1), x(2), nPoints));  % Column indices
index = sub2ind(size(mat), rIndex, cIndex);     % Linear indices
mat(index) = 255;  % Set the line pixels to the max value of 255 for uint8 types

You can then visualize the line and the filtered version with the following:

subplot(1, 2, 1);
image(mat);        % Show original line image
colormap(gray);    % Change colormap
title('Line');

subplot(1, 2, 2);
h = fspecial('gaussian', 20, 10);  % Create filter
filteredImg = imfilter(mat, h);    % Filter image
image(filteredImg);                % Show filtered line image
title('Filtered line');

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