alt Hacker NewsOLED is fundamentally not sample and hold, because it is using PWM, right?
Ignoring switching costs, keeping a sample-and-hold LED at 0%, 50% and 100% brightness all cost zero energy. For an OLED, the costs are closer to linear in the duty cycle (again, ignoring switching costs, but those are happening much faster than the framerate for OLED, right?)
(Also, according to another comment, the panel manufacturer says this is TFT, not OLED, which makes a lot more sense.)
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PWM still counts as sample-and-hold, because it sustains the brightness throughout the duration of a frame, resulting in significant motion blur. The converse are impulse-driven displays like CRT and plasma.
LED backlights using PWM likewise don’t change the sample-and-hold nature of LCD panels.
My understanding is that PWM switching costs aren’t negligible, and that this contributes to why PWM frequencies are often fairly low.
I don't believe LED-pixel displays use PWM. I would expect them to use bit planes: for each pixel transform the gamma-compressed intensity to the linear photon-proportional domain. Represent the linear intensity as a binary number. Start with the most significant bit, and all pixels with that bit get a current pulse, then for the next bitplane all the pixels having the 2nd bit set are turned on with half that current for the same duration, each progressive bitplane sending half as much current per pixel. After the least significant bitplane has been lit each pixel location has emitted a total number of photons proportional to what was requested in the linear domain.