CODEWITHSUNDEEP
image-processingcomputer-visionnormalization
Autonomous
Autonomous

Reputation: 9075

HOG features on different scales

Suppose we calculate HOG features of image patches of different sizes, ranging from 64 * 64 to 128 * 128. Now, if we want to do k-means on these, should we normalize the patches which belong to different scale? I know HOG features are normalized, but does scale matter?

Upvotes: 3

Views: 2318

Answers (1)

Raluca
Raluca

Reputation: 280

Normally, the HOG representations are normalized. However, you must be careful to the block size. In fact, you must have the same number of blocks, whatever the size of the image. Otherwise, you obtain descriptors of different lengths and the k-means cannot be performed. This means that when having larger images, you will have larger blocks. The resulting histograms will contain information from more gradients, so they aren’t invariant at this stage. However, by applying the histogram normalization, the scale invariance of the final descriptor is obtained.

Yet, if you are not sure if the histogram normalization is well performed or not, you can extract the descriptor for an image and its resized version and compare them. Good luck!

Upvotes: 4

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