K-means on a gray scale image

Question

Iremsu Savas 2018-10-24

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https://ww2.mathworks.cn/matlabcentral/answers/425839-k-means-on-a-gray-scale-image

评论： Image Analyst 2020-9-2

Hello everyone, I have a grayscale image 'lena.bmp' and I am trying to apply k-means color quantization. I found the following code but I have some points that are not clear in my mind: 1)Why we need to convert the image format to double? 2)While I am writing "pixel_labels = reshape(cluster_idx,nrows,ncols);" in the code what excatly it is doing? 3)Why did I need to write the square brackets inside this "imshow(pixel_labels,[])" ? The code is here:

Image=imread('lena.bmp');
Image = im2double(Image);
nrows = size(Image,1);
ncols = size(Image,2);
Image = reshape(Image,nrows*ncols,1); 
Colors = 4;
[cluster_idx, cluster_center] = kmeans(Image,Colors,'distance','sqEuclidean');  
pixel_labels = reshape(cluster_idx,nrows,ncols);
imshow(pixel_labels,[]);

Thank you so much.

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Answer 1

Adam 2018-10-24

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https://ww2.mathworks.cn/matlabcentral/answers/425839-k-means-on-a-gray-scale-image#answer_343171

在 MATLAB Online 中打开

1. kmeans only supports double or single inputs. It works in floating point so integers wouldn't make sense.

2.

doc reshape

will answer this. It does pretty much exactly what it says - it reshapes your output back to the number of rows and columns of your image so that you have an image back rather than just a vector of class indices.

3.

doc imshow

describes the different scaling you can do with imshow. This syntax is the 3rd in the list.