Visualization of absolute values of Saab filter responses and the detection heat maps for DC, AC1, AC11 and AC26 four channels, where DC and AC1 are low-frequency channels, AC11 is a mid-frequency channel, and AC26 is a high-frequency channel. Cold and warm colors in heat maps indicate a higher probability of being real and fake in the corresponding location, respectively. The ground truth is that the whole image is a fake one.