An encoder that performs quantization based on a deadzone and a video processing system including the encoder are provided. The encoder includes: a domain transform unit configured to transform first image data of a spatial domain into second image data of a frequency domain including first to N-th pieces of frequency data (wherein N is an integer equal to or greater than 1); a deadzone determination unit including a human visual system (HVS) table including human visual frequency sensitivities and configured to determine, based on the HVS table, a deadzone regarding each of the first to N-th pieces of frequency data; and a quantization unit configured to perform, based on the deadzone, quantization regarding the second image data.