OpenCV running kmeans algorithm on an image

Question

I am trying to run kmeans on a 3 channel color image, but every time I try to run the function it seems to crash with the following error:

OpenCV Error: Assertion failed (data.dims <= 2 && type == CV_32F && K > 0) in unknown function, file ..\..\..\OpenCV-2.3.0\modules\core\src\matrix.cpp, line 2271

I've included the code below with some comments to help specify what is being passed in. Any help is greatly appreciated.

// Load in an image
// Depth: 8, Channels: 3
IplImage* iplImage = cvLoadImage("C:/TestImages/rainbox_box.jpg");

// Create a matrix to the image
cv::Mat mImage = cv::Mat(iplImage);

// Create a single channel image to create our labels needed
IplImage* iplLabels = cvCreateImage(cvGetSize(iplImage), iplImage->depth, 1);

// Convert the image to grayscale
cvCvtColor(iplImage, iplLabels, CV_RGB2GRAY);

// Create the matrix for the labels
cv::Mat mLabels = cv::Mat(iplLabels);

// Create the labels
int rows = mLabels.total();
int cols = 1;
cv::Mat list(rows, cols, mLabels .type());
uchar* src;
uchar* dest = list.ptr(0);
for(int i=0; i<mLabels.size().height; i++) 
{
    src = mLabels.ptr(i);
    memcpy(dest, src, mLabels.step);
    dest += mLabels.step;
}
list.convertTo(list, CV_32F);

// Run the algorithm
cv::Mat labellist(list.size(), CV_8UC1);
cv::Mat centers(6, 1, mImage.type());
cv::TermCriteria termcrit(CV_TERMCRIT_EPS+CV_TERMCRIT_ITER, 10, 1.0);
kmeans(mImage, 6, labellist, termcrit, 3, cv::KMEANS_PP_CENTERS, centers);

karlphillip · Accepted Answer · 2011-08-10 19:46:00Z

11

The error says all: Assertion failed (data.dims <= 2 && type == CV_32F && K > 0)

These are very simple rules to understand, the function will work only if:

mImage.depth() is CV_32F
if mImage.dims is <= 2
and if K > 0. In this case, you define K as 6.

From what you stated on the question, it seems that:

IplImage* iplImage = cvLoadImage("C:/TestImages/rainbox_box.jpg");`

is loading the image as IPL_DEPTH_8U by default and not IPL_DEPTH_32F. This means that mImage is also IPL_DEPTH_8U, which is why your code is not working.

answered Aug 10, 2011 at 19:46

karlphillip

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5 Comments

Seb Over a year ago

So does this mean that I have to load it in as a grayscale image?

karlphillip Over a year ago

No, it doesn't. iplImage->depth and iplImage->nChannels are two different things. You need to convert iplImage to it's IPL_DEPTH_32F equivalent. That's all. Check this answer on how to do that: stackoverflow.com/questions/6349493/…

Seb Over a year ago

I just tried the convert function and it crashes on me. "IplImage* ipl32Image = cvCreateImage(cvGetSize(iplImage), IPL_DEPTH_32F, 1); cvConvert(iplImage, ipl32Image);" with the error "OpenCV Error: Assertion failed (src.size == dst.size && src.channels() == dst.ch annels()) in unknown function, file ..\..\..\OpenCV-2.3.0\modules\core\src\convert.cpp, line 1177". It seems that I'll have to either split up the channels or I'll have to load in a grayscale image

karlphillip Over a year ago

It's crashing because you assume that the number of channels of iplImage is 1. Fix it to cvCreateImage(cvGetSize(iplImage), IPL_DEPTH_32F, iplImage->nChannels);

Seb Over a year ago

Beautiful! I misinterpreted the "mImage.dims" thinking that it only wanted that to be a 1 or a 2. Thank you so very much. :D

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