I = imread('coins.png'); level = graythresh(I); BW = im2bw(I,level); imshow(BW) 上面是MATLAB文档中使用灰度图像的示例。如何使它与索引图像（如
在
这篇文章中 ？
回答：
您可以先使用
IND2GRAY函数将索引图像及其
色彩图转换为灰度图像：
[X,map] = imread('SecCode.php.png'); %# Read the indexed image and colormap grayImage = ind2gray(X,map); %# Convert to grayscale image 然后，您可以应用上面的代码：
level = graythresh(grayImage); %# Compute threshold bwImage = im2bw(grayImage,level); %# Create binary image imshow(bwImage); %# Display image
编辑：
如果您想对任何类型的图像都采用这种通用方法，则可以采用以下一种方法：
%# Read an image file: [X,map] = imread('an_image_file.some_extension'); %# Check what type of image it is and convert to grayscale: if ~isempty(map) %# It's an indexed image if map isn't empty grayImage = ind2gray(X,map); %# Convert the indexed image to grayscale elseif ndims(X) == 3 %# It's an RGB image if X is 3-D grayImage = rgb2gray(X); %# Convert the RGB image to grayscale else %# It's already a grayscale or binary image grayImage = X; end %# Convert to a binary image (if necessary): if islogical(grayImage) %# grayImage is already a binary image bwImage = grayImage; else level = graythresh(grayImage); %# Compute threshold bwImage = im2bw(grayImage,level); %# Create binary image end %# Display image: imshow(bwImage); 除某些离群值（例如
TIFF图像的备用颜色空间 ）外，这应涵盖
大多数图像类型。
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