About the GLCM and textures

The Gray Level Co-occurrence Matrix1 (GLCM) and associated texture feature calculations are image analysis techniques. Given an image composed of pixels each with an intensity (a specific gray level), the GLCM is a tabulation of how often different combinations of gray levels co-occur in an image or image section. Texture feature calculations use the contents of the GLCM to give a measure of the variation in intensity (a.k.a. image texture) at the pixel of interest.

Echoview offers a GLCM texture feature operator that produces a virtual variable which represents a specified texture calculation on a single beam echogram.

The virtual variable is created in the following way (using the settings on the GLCM texture page of the Variable properties dialog box identified in bold):

1. Quantize the image data. Each sample on the echogram is treated as a single image pixel and the value of the sample is the intensity of that pixel. These intensities are then further quantized into a specified number of discrete gray levels as specified under Quantization.
2. Create the GLCM. It will be a square matrix N x N in size where N is the Number of levels specified under Quantization. The matrix is created as follows:
   1. Let s be the sample under consideration for the calculation.
   2. Let W be the set of samples surrounding sample s which fall within a window centered upon sample s of the size specified under Window Size.
   3. Considering only the samples in the set W, define each element i,j of the GLCM as the number of times two samples of intensities i and j occur in specified Spatial relationship (where i and j are intensities between 0 and Number of levels-1) .
      
      The sum of all the elements i, j of the GLCM will be the total number of times the specified spatial relationship occurs in W.
   4. Make the GLCM symmetric:
      1. Make a transposed copy of the GLCM
      2. Add this copy to the GLCM itself
         
         This produces a symmetric matrix in which the relationship i to j is indistinguishable for the relationship j to i (for any two intensities i and j). As a consequence the sum of all the elements i, j of the GLCM will now be twice the total number of times the specified spatial relationship occurs in W (once where the sample with intensity i is the reference sample and once where the sample with intensity j is the reference sample), and for any given i, the sum of all the elements i, j with the given i will be the total number of times a sample of intensity i appears in the specified spatial relationship with another sample.
   5. Normalize the GLCM:
      1. Divide each element by the sum of all elements
         
         The elements of the GLCM may now be considered probabilities of finding the relationship i, j (or j, i) in W.
3. Calculate the selected Feature. This calculation uses only the values in the GLCM. See:
   • Energy,
   • Entropy,
   • Contrast,
   • Homogeneity,
   • Correlation,
   • Shade or
   • Prominence
4. The sample s in the resulting virtual variable is replaced by the value of this calculated feature.

See also

GLCM texture feature operator
GLCM texture page of Variable properties dialog box

1. Newcomers to this topic are advised to read the GLCM Tutorial at http://www.fp.ucalgary.ca/mhallbey/ and pursue any further reading if necessary.

Echoview Help file 5.2.21 for Echoview 5.2.55 Monday 21st May 2012

Please report any errors or omissions to support@echoview.com.