Gabor filter can be simply defined as a Gaussian modulated sinusoid with a capability of multiresolution analysis. The extracted features represent the energy of each filter magnitude response.
More information can be found in section 6.8 of the PhD thesis on the use of Gabor filter for texture analysis in medical images: http://omar.alkadi.net/wp-content/uploads/Al-Kadi_PhD_Thesis.pdf
Take all three filtered channel data (except the approximation channel), divide each channel matrix into for example 9 *9 blocks, calculate the mean and variance of each block, construct a feature vector, depending on your need, which contains the mean and variance information, for comparison with similar data in other images.