Texture Recognition

One way to analyze the texture pattern in an image is through Local Binary Pattern (LBP). The computation of the LBP is done as follows:

(1) for every pixel location, get the difference of the center pixels from each of its eight neighboring pixel.
(2) set a threshold in which all the negative values are zeroes, otherwise ones.
(3) set a fixed weight for each of the 8 position of the neighbor, that is, $2^{n-1}$ for the nth neighbor where the movement is in clockwise direction.  Multiply this weight to the corresponding thresholded values.
(4) compute the sum of these products. The sum is the LBP value for that neighborhood.

The summary of the computation of LBP is illustrated in the figure below

Three texture classes that were considered for this activity are sand, sponge and wood. At least five samples for each class were considered. The first set of texture samples is shown below. 

Sand texture samples in grayscale. 

Information about the texture are presented here through histogram. The LBP histogram for each sample of the sand texture is shown below. Aside from the peak at the very dark and the very light values or the two ends of the histogram, the other bins don't have drastic difference in values. This histogram pattern was consistent for all five sand samples. 

LBP histogram of five sand texture samples.

Sponge texture samples

Sponge texture samples in grayscale.

The LBP histogram for each sample of the sponge texture. Ideally, different texture have different histogram. The difference of the sand LBP histogram between the sponge LBP histogram are easily noticeable. The histogram of the sponge texture as shown below have sudden drop and rise in their values but this is relatively the same result for all five sponge textures. 

Wood texture samples

Wood texture samples in grayscale.

Lastly, the LBP histogram for each sample of the wood textures was acquired. It was observed from the figure below that the three fork shape at the middle was prominent for all the histograms. But for other part, we can reasonably say that they are similar to each other. 

But for strong argument sake, I presented below their corresponding histograms using smaller bins for this set of texture. Now, we can observed the similarity between the five histograms better. The middle values have relatively negligible density as compared to the rest where the the right side seems to have heavier weight than the left side. This is different from the other textures because the LBP histograms of sand and sponge have pretty much symmetric right and left sides.

References

[1] Matti Pietikäinen. Local Binary Patterns. 2010. http://www.scholarpedia.org/article/Local_Binary_Patterns