We review the role of acousto-optic (AO) modulators in programmable real-time image processing. Using one AO cell, 1D high pass filtering and edge enhancement has recently been demonstrated. Two AO cells in tandem can be used to remove asymmetries for using one AO cell. We also show notch filtering characteristics of an AO cell by developing a technique to determine the spatial transfer functions numerically for various cases of beam incidence on an AO modulator. Normal incidence and incidence at twice the Bragg angle are investigated as examples.