A technique for quantitatively measuring the image retention is suggested. This work focuses on dark image retention, which occurs during the reset period. To investigate the dark image retention phenomenon, characteristics of reset discharge were observed in accordance with the slope of the reset pulse. The temporal behaviors of luminance, chromatistic values, and infra red emission were observed with the black-level image after a five-minute repeatedly strong discharge. The image retention time of the luminance and chromatistic values increased with a decrease in the rising time of the reset ramp pulse. For the case of infrared (IR) emission, there was no clear tendency, in contrast with the image retention or temporal image sticking phenomenon. The results indicate that measurement of the temporal behaviors of luminance and chromatistic values provide suitable measurement for investigating the image retention in AC plasma display panels (PDPs), whereas the IR emission does not provide a useful guide in this regard.