16. An ultrasound diagnostic apparatus, comprising:processing circuitry configured to

acquire, as a first data group, a plurality of pieces of ultrasound image data, each of the plurality of pieces of ultrasound image data being acquired at a different deflection angle, of a plurality of different deflection angles generated by first ultrasound scanning in a first mode in which the deflection angles for ultrasound transmission and reception are changed between a plurality of frames, the plurality of different deflection angles including a first deflection angle and each piece of ultrasound image data corresponding to a frame of the plurality of frames, acquire, as a second data group, first received signals, each of the first received signals corresponding to one of a plurality of reception scan lines, the first received signals being generated by second ultrasound scanning in a second mode in which the deflection angles for ultrasound transmission and reception are changed, and acquire, as a third data group, second received signals, each of the second received signals corresponding to one of the plurality of reception scan lines, the second received signals being generated by third ultrasound scanning in a third mode in which a plurality of reflected waves at the different deflection angles for ultrasound reception are received;

in the first mode, calculate first coefficients, each first coefficient corresponding to a spatial position of a plurality of spatial positions in a first piece of ultrasound image data and being separately calculated for each spatial position, of the acquired plurality of pieces of ultrasound image data, acquired at the first deflection angle, each of the first coefficients being calculated based on a signal value or a pixel value at a corresponding spatial position, of the plurality of spatial positions, in at least one of the acquired plurality of pieces of ultrasound image data acquired at a deflection angle, of the plurality of different deflection angles, other than the first deflection angle, and in the second and the third modes, calculate second coefficients, each second coefficient corresponding to one depth of a plurality of depths on a first reception scan line corresponding to the first deflection angle, each second coefficient being separately calculated for each one depth, the second coefficient being calculated based on a first signal value or a first pixel value at the one depth and being derived from the first received signals, when in the second mode, or the second received signals, when in the third mode, corresponding to at least one reception scan line, of the plurality of reception scan lines, having a deflection angle other than the first deflection angle;

in the first ultrasound scanning, multiply, by the first coefficients, second signal values or second pixel values corresponding to the plurality of spatial positions in the first piece of ultrasound image data corresponding to the first deflection angle, or third signal values or third pixel values corresponding to the plurality of spatial positions in a piece of image data that is obtained by compounding the plurality of pieces of ultrasound image data acquired at the plurality of different deflection angles including the first deflection angle, and in the second ultrasound scanning and the third ultrasound scanning, multiply, by the second coefficients, fourth signal values or fourth pixel values derived from the first received signals, when in the second mode, or the second received signals, when in the third mode, corresponding to the first reception scan line or a signal obtained by compounding the first received signals, when in the second mode, or the second received signals, when in the third mode, corresponding to the reception scan lines at the plurality of deflection angles including the first deflection angle, the fourth signal values or the fourth pixel values having values at the plurality of depths on the first reception scan line;

when the processing circuitry uses the first data group and at least one group of the second data group and the third group, (1) perform first multiplication, the first multiplication being multiplication of at least one of the data values in the first data group by at least one of the first coefficients, and/or (2) perform second multiplication, the second multiplication being multiplication of at least one of the data values in the at least one group by at least one of the second coefficients;

when the processing circuitry does not use the first data group and uses the second data group and the third data group are obtained, perform third multiplication, the third multiplication being multiplication of at least one of the data values in the at least one of the second data group and the third data group by at least one of the second coefficients;

when the processing circuitry uses the first data group, but does not perform the first multiplication, perform a compounding process on the first data group;

when the processing circuitry does not use the second data group, but does not perform the second multiplication nor the third multiplication, perform a compounding process on the second data group; and

when the processing circuitry uses the third data group, but does not perform the second multiplication nor the third multiplication on the third data group, perform a compounding process on the third data group.