size differ when processing

In my code below can u tell why the number of elements are different or size is different

>> img=imread('peppers.png');
>> flatImg = double(reshape(img,size(img,1)*size(img,2),size(img,3)));
idx = kmeans(flatImg,3)

size(flatImg)

196608           3

size(idx)

196608           1

please provide assistance

Answer 1

[Image Analyst]

You have 196608 pixels. In flatImg you rearranged them into rows where each column is the red, green, and blue values.

With kmeans, each of the 196608 pixels is classified as a "1", "2", or a "3" depending on its color, so it's a 1D array. There is no information along any second dimension like there was with flatImg.

There is no reason why they should be the same size because they represent different things. Do you think they should?

[kash]

So how to get information along 2nd and 3rd dimensions or else is these information enough for getting accurate results for rgb image

[Image Analyst]

What second and third dimension? You have a list of classifications for each pixel. For example, pixel 1 might be class 3 and pixel 2 might be class 2, etc. You have to reshape that "idx" into a 2D image (the same size as your original image) if you want the classified image. It will have the same number of gray levels as classes you have, obviously.

[kash]

ok thanks Analyst