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Mar 17, 2013

Raymond Soneira, Displaymate's display guru (and our friend) has previously criticized Samsung for the lack of calibration on their AMOLED displays - the colors are too saturated, the whites are too blue, and the intensity scales are too steep. This is hopefully going to change with the S4 however. Samsung is including a new feature in the S4 called Adapt Display that offers seven automatic modes and four manual modes - to provide the optimal viewing experience.

Samsung S4 Adapt Display photo

As Raymond points out, Samsung's own S4 site shows a CIE chromaticity diagram and a gray scale level picker (see screenshot above). This leads Raymond to believe that the S4 will have extensive color, white-point, and display calibration adjustments. This could be a "major display advancement and a win for Samsung and AMOLED displays" - according to Raymond.

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Could you provide some details about how exactly PWM is related to color calibration/tuning of OLED displays? AFAIK, PWM can (though it is not necessary and undesirable in general) be used to control overall brightness of entire OLED display while individual subpixels (and therefore colors) are controlled via voltage/current only.

MT, here's the explanation Raymond sent us:

Plasma displays, DLP, and Samsung OLEDs all use Pulse Width Modulation to independently control the intensity (Luminance) of every single R,G,B sub-pixel in the entire display. In Pulse Width Modulation each sub-pixel is continuously switched at a very high rate (typically greater than 100KHz) between the fully Off and fully On states by the display controller and AM Active Matrix. The percentage of time that a sub-pixel spends in the On state determines its particular observed visual Luminance. For example, within an given image refresh frame, if a particular sub-pixel spends 25% of the time in the On state and 75% in the Off state, it will have 25% of the peak Luminance for that sub-pixel at that instant. This makes it easy to digitally control the entire image and apply all of the desired display calibrations digitally as well.

The statement made by the reader that the overall brightness is controlled by PWM and individual sub-pixels are controlled by voltage [not current] applies exactly to LCDs, where the brightness of the LED or CCFL backlight is controlled by PWM. OLEDs do not have a backlight so this statement does not apply to OLEDs.

Thanks. I know well what is PWM itself as well as that OLEDs do not have a backlight.

Backlight absence does not necessarily mean that PWM is not used to control overall brightness of the display, and moreover does not mean that PWM should necessarily be used to control individual subpixels.

For example, as far as I know, Sony’s professional broadcasting monitor PVM-1741 uses PWM to control overall brightness of the display: