A psychophysical experiment was conducted in which observers compared the saturation and brightness between high-dynamic-range images that had been modulated in chroma and achromatic lightness. Models of brightness which account for the Helmholtz-Kohlrausch effect include both chromatic and achromatic inputs into brightness metrics, and this experiment was an exploration of whether these metrics could be expanded to images. The observers consistently judged saturation in agreement with the predictions of our color appearance modeling. However, some unexpected results and differences between observers in their methods for judging brightness indicates that further modeling, including spatial effects of color perception, need to be included to apply our model of the Helmholtz-Kohlrausch effect to images.