Moments

Using the Blob Analysis module, you can also calculate the moments used to find the center of gravity, as well as other grayscale and binary moments. To calculate a moment of a specified order in X and Y (general moment), enable the M_MOMENT_GENERAL feature for calculation using MblobControl; then specify the X and Y order of the moment to calculate using MblobControl with M_MOMENT_GENERAL_ORDER_X and M_MOMENT_GENERAL_ORDER_Y, respectively. Select whether to calculate the ordinary or the central moment using MblobControl with M_MOMENT_GENERAL_MODE. Central moments use coordinates that are relative to the center of gravity of the blob, and therefore are independent of a blob's position within the image; whereas, ordinary moments are affected by the blob position because they use coordinates relative to the top-left corner of the image. Use MblobGetResult with M_MOMENT_GENERAL to retrieve the result.

You could alternatively enable the calculation of the M_MOMENT_FIRST_ORDER, M_MOMENT_SECOND_ORDER and/or M_MOMENT_THIRD_ORDER group of features for calculation using MblobControl. These groups of features include only the more common moments (for example, MblobGetResult with M_MOMENT_X0_Y1, M_MOMENT_X0_Y2 or M_MOMENT_X0_Y3). These common moments are calculated faster than the general moment.

You could also enable the calculation of hu moment invariants using MblobControl with M_MOMENT_THIRD_ORDER. Hu moments are a set of seven moments calculated using central moments. Hu moments are invariant to translation, rotation and scaling.