A method for determining an afterimage level of a display device, comprising: displaying an image having a single color value on the display device and detecting the brightness value of the display device, denoted as brightness value of the display device before the afterimage test; performing an afterimage test for the display device by displaying an image for the afterimage test, wherein a test image comprising a plurality of unit areas is displayed in the afterimage test; after the afterimage test, switching the image displayed by the display device to the image displayed before the afterimage test and detecting the brightness values displayed by the display device, denoted as brightness values of the display device after the afterimage test; wherein the brightness value of the display device before the afterimage test is the detected brightness value of the display device in the case of displaying the image having a single color value; calculating, for each brightness value (Y(bl), Y) of the display device after the afterimage test, a brightness difference of the afterimage as the absolute value of the difference between the brightness value (Y(bl), Y) of the display device after the afterimage test and the brightness value of the display device before the afterimage test; calculating, for each brightness value (Y(bl), Y) of the display device after the afterimage test, a brightness variation index, an area index, and an afterimage index, wherein the brightness variation index is equal to the ratio of the brightness difference of the afterimage with respect to the brightness value of the display device before the afterimage test, wherein the area index is equal to the ratio of the number of unit areas with the brightness value (Y(bl), Y) of the display device after the afterimage test with respect to the number of unit areas forming the total display area of the display device; and wherein the afterimage index for a brightness value is equal to the product of the brightness variation index for said brightness value and the calculated area index for said brightness value; and determining the afterimage level of the display device according to the sum of the afterimage indexes for each brightness value (Y(bl), Y). displaying an image having a single color value on the display device and detecting the brightness value of the display device, denoted as brightness value of the display device before the afterimage test; performing an afterimage test for the display device by displaying an image for the afterimage test, wherein a test image comprising a plurality of unit areas is displayed in the afterimage test; after the afterimage test, switching the image displayed by the display device to the image displayed before the afterimage test and detecting the brightness values displayed by the display device, denoted as brightness values of the display device after the afterimage test; wherein the brightness value of the display device before the afterimage test is the detected brightness value of the display device in the case of displaying the image having a single color value; calculating, for each brightness value (Y(bl), Y) of the display device after the afterimage test, a brightness difference of the afterimage as the absolute value of the difference between the brightness value (Y(bl), Y) of the display device after the afterimage test and the brightness value of the display device before the afterimage test; calculating, for each brightness value (Y(bl), Y) of the display device after the afterimage test, a brightness variation index, an area index, and an afterimage index, wherein the brightness variation index is equal to the ratio of the brightness difference of the afterimage with respect to the brightness value of the display device before the afterimage test, wherein the area index is equal to the ratio of the number of unit areas with the brightness value (Y(bl), Y) of the display device after the afterimage test with respect to the number of unit areas forming the total display area of the display device; and wherein the afterimage index for a brightness value is equal to the product of the brightness variation index for said brightness value and the calculated area index for said brightness value; and determining the afterimage level of the display device according to the sum of the afterimage indexes for each brightness value (Y(bl), Y).