Abstract: Automatic music transcription plays an important role in music signal processing.This paper presents a computationally efficient approach to automatic polyphonic music transcription.The approach employs the Resonator Time-Frequency Image (RTFI) as a basic time-frequency analysis tool.The approach is mainly composed of two stages: energy-based onset detection and multiple pitch estimation.The proposed method makes preliminary pitch estimations by a simple peak-picking in the pitch energy spectrum,which is produced from original energy spectrum according to harmonic grouping principle;and then the incorrect estimations are cancelled according to spectral irregularity or some assumptions about harmonic structures of music notes.