如何在Matlab中找到并突出显示图像中最亮的区域

Question

Dears，

我想恳请你的支持。我的目标是找到RGB图像中最亮的区域，并在没有额外工具的情况下高亮显示它。请看下面的例子。

rgbImage = imread( 'Zoom1_WhiteImage.png' );
imshow(rgbImage);
[rows, columns, numberOfColorChannels] = size(rgbImage)
[x, y] = meshgrid(1:columns, 1:rows);
% Extract the individual red, green, and blue color channels.
% Need to cast to double or else x and y will be clipped to 255 when we concatenate them.
if numberOfColorChannels == 1
% Leave as gray scale.
% Get array listing [r, g, b, x, y].  Using (:) will turn all the 2-D arrays into column vectors.
output = [rgbImage(:), x(:), y(:)];
else
redChannel = double(rgbImage(:, :, 1));
greenChannel = double(rgbImage(:, :, 2));
blueChannel = double(rgbImage(:, :, 3));
% Get array listing [r, g, b, x, y].  Using (:) will turn all the 2-D arrays into column vectors.
output = [redChannel(:), greenChannel(:), blueChannel(:), x(:), y(:)];
end
[rows, columns] = find(rgbImage == 155);
imshow(rgbImage);
hold on

不幸的是，我正在努力处理如何绘制应该覆盖灰色图像的点。

你能帮我完成代码吗？

Answer 1

我建议您阅读MATLAB中的逻辑索引——这是一个非常强大的概念，它允许您跳过大多数尝试做的事情，方法是将数组扁平化，并使用meshgrid创建单独的索引数组。例如，这里有一篇文章在底部介绍了逻辑索引。

我已经修改并添加到您的代码中，因此它使用逻辑索引来完成任务。我在R2019b中对此进行了测试。

rgbImage = imread( 'Zoom1_WhiteImage.png' );
imshow(rgbImage);
[rows, columns, numberOfColorChannels] = size(rgbImage)
% This is unnecessary - the 'find' command will generate the indices 
%   without you preparing a matrix of them:
% [x, y] = meshgrid(1:columns, 1:rows);   
if numberOfColorChannels == 1
% No need to flatten the image, or combine it with indices:
%output = [rgbImage(:), x(:), y(:)];
brightness = rgbImage;  % For a 1 channel image, brightness is the same as the original pixel value.
else
%     redChannel = double(rgbImage(:, :, 1));
%     greenChannel = double(rgbImage(:, :, 2));
%     blueChannel = double(rgbImage(:, :, 3));
% Get array listing [r, g, b, x, y].  Using (:) will turn all the 2-D arrays into column vectors.
%     output = [redChannel(:), greenChannel(:), blueChannel(:), x(:), y(:)];
% For an RGB image, the brightness can be estimated in various ways, here's one standard formula: 
brightness = (0.2126*rgbImage(:, :, 1) + 0.7152*rgbImage(:, :, 2) + 0.0722*rgbImage(:, :, 3));
end
% Establish a brightness threshold - pixels brighter than this value will
% be highlighted
threshold = 215;
% Create a zero-filled mask of equal size to the image to hold the
% information of which pixels met the brightness criterion:
mask = zeros(rows, columns, 'logical');
% Assign "1" to any mask pixels whose corresponding image pixel met the
% brightness criterion:
mask(brightness > threshold) = 1;
figure;
% Overlay and display mask. imoverlay was introduced in R2017, but the 
% syntax has changed a bit, so check the version you're using. You can also
% use imfuse, or imshowpair, or make your own image blending algorithm, 
% depending on how you want it to look.
imshow(imoverlay(rgbImage, mask, 'red'));
hold on