SNAP Texture Analysis


#1

Dear all,

I havce a question converning the GLCM

If you select SNAP -> Raster -> Image Analysis- > Texture Analysis -> Grey Level co-occurene matrix, a window called GLCM will open. At the tab processing parameters, there are several parameters:

  • Quantizer
  • Quantization Levels
  • Displacement

They are not explained in the help module.

What exactly do these paremeters mean?

Thanks a lot…


#2

Hi,

  • Quantizer: If you select probabilistic option, then your GLCM matrix is expressed as probabilities instead of counting the total number of occurrences (probabilistic approach is preferred)

  • Quantization Levels: Quantization Levels is the number of possible values that your final image will have (e.g 8bit has 256 possible values while 16bit you will have a matrix 65536 x 65536 = 429,426,720 cells ). The higher the quantized levels, less information loss. On the other hand, the lower the quantized levels, more information loss. Keep in mind that, increasing the quantized level to the maximum, the procedure will take very long time and you will end up having a huge matrix which will be very hard to manipulate. (32 or 64 grey levels are proffered)

  • Displacement: Before GLCM matrix is calculated, a distance must be defined first. GLCM calculates how often different combination of pixels brightness values occur in an image. If you define a distance of 1, this means one pixel to the east from your reference pixel. distance of 4, it means 4 pixel to the east from your reference pixel. Most authors have proved that the optimum values for distance are between 1 and 3.

for more details please look at: https://www.researchgate.net/publication/315776784_GLCM_Texture_A_Tutorial_v_30_March_2017


#3

Great! Thanks a lot…


#4

Yes, the documentation should be more exhaustive here.
We should consider this document and describe the processing parameters in more detail.


#5

Could you please tell me that in GLCM processing parameters, in the Angle box, what does ALL option indicate. Does it take the average of all the directions in which texture was calculated or is it something else? I understand how texture is calculated individually for each direction.


#6

I don’t fully understand it but Eichkitz et al. 2013/2014 were one of the first to propose GLCM textures in multiple directions: