A method for calibrating an OLED display device having four or more channels (R, G, B, W; 70, 72, 74, 76), including three main channels (R, G, B; 70, 72, 74) which include in their gamut a desired display white point, and one or more further channels (W; 76), said OLED display device also having one or more individual adjustment controls for each channel, said method comprising the steps of: a) displaying a first target using a low level code value for each channel (R, G, B, W) of the display; b) measuring and recording the luminance and chromaticity coordinates of the displayed first target; c) displaying a second target using a minimum code value for each of the further channels, and a set of non-minimum code values, such set including one non-minimum code value for each of the three main channels (R, G, B); d) measuring the luminance and chromaticity coordinates of the displayed second target; e) adjusting the individual adjustment controls for each of the three main channels (R, G, B) so that the chromaticity coordinates of the second target approximately match the chromaticity coordinates of the desired display white point; f) recording the resulting values of the individual adjustment controls for each of the three main channels (R, G, B) and the corresponding luminance and chromaticity coordinate measurements; g) repeating steps c) through f) one or more times for each of a number of additional selected non-minimum code value sets; h) displaying a third target using, for a first main channel (R, G, B), the value(s) of the individual adjustment control(s) for that channel recorded in step f) corresponding to a selected non-minimum code value set, and using, for each of the other channels, a minimum code value; i) measuring and recording the luminance and chromaticity coordinates of the displayed third target; j) repeating steps h) through i) for each remaining main channel (R, G, B); k) displaying a fourth target using a selected code value for a first further channel, and a minimum code value for each of the other channels; l) measuring and recording the luminance and chromaticity coordinates of the displayed fourth target; m) repeating steps k) through I) for one or more of a number of additional selected code values of the first further channel; and n) repeating steps k) through m) for each remaining further channel, characterized in that for at least one target, a buck pattern (60; 62) is displayed on the OLED display device, said buck pattern (60; 62) comprising, across the at least one target, pixels driven with the selected code values and pixels driven with relatively lower code values than the selected code values. a) displaying a first target using a low level code value for each channel (R, G, B, W) of the display; b) measuring and recording the luminance and chromaticity coordinates of the displayed first target; c) displaying a second target using a minimum code value for each of the further channels, and a set of non-minimum code values, such set including one non-minimum code value for each of the three main channels (R, G, B); d) measuring the luminance and chromaticity coordinates of the displayed second target; e) adjusting the individual adjustment controls for each of the three main channels (R, G, B) so that the chromaticity coordinates of the second target approximately match the chromaticity coordinates of the desired display white point; f) recording the resulting values of the individual adjustment controls for each of the three main channels (R, G, B) and the corresponding luminance and chromaticity coordinate measurements; g) repeating steps c) through f) one or more times for each of a number of additional selected non-minimum code value sets; h) displaying a third target using, for a first main channel (R, G, B), the value(s) of the individual adjustment control(s) for that channel recorded in step f) corresponding to a selected non-minimum code value set, and using, for each of the other channels, a minimum code value; i) measuring and recording the luminance and chromaticity coordinates of the displayed third target; j) repeating steps h) through i) for each remaining main channel (R, G, B); k) displaying a fourth target using a selected code value for a first further channel, and a minimum code value for each of the other channels; l) measuring and recording the luminance and chromaticity coordinates of the displayed fourth target; m) repeating steps k) through I) for one or more of a number of additional selected code values of the first further channel; and n) repeating steps k) through m) for each remaining further channel,