Monochrome LCD Video Hacks Galore!

[Wenting Zhang] is clearly a lover of previous school STN Liquid crystal display displays, and was asking yourself how various more mature moveable products managed to travel monochrome LCDs panels with various grey amounts. If the screen controller supports many bits per pixel, it can use various procedures, these kinds of as PWM, in buy to develop a pseudo-grayscale graphic. But, what if you have a monochrome-only display screen controller? With a adequately substantial pixel clock, can you use software program on the software side of items to flip people pixels in these kinds of a method as to give a sensible searching grayscale picture?

Simple dithering – do not glimpse much too shut!
PDM greyscale approximation in a 1-bit display

[Wenting] goes through a number of strategies, exhibiting the resulting graphic top quality in a clear, systematic fashion. The very first strategy is to use a classic dithering strategy. For every pixel, it is established to black if the grey price is beneath some threshold. The resulting error value, is then propagated to neighbouring pixels. This mistake diffusion process smears the mistake out over the full exhibit, so spatially speaking, on regular the pixel values correspond approximately to the initial gray values. But, the pixels on their own are even now possibly on or off. This isn’t really ample. The future plan is to PWM the individual pixels above numerous frames, to approximate unique gray degrees. But, that gives a worst case helpful refresh amount of 8 Hz with a PWM interval of 15 frames, at 120 fps, and that flickers. Badly. 1 way to mitigate that is to change to PDM (pulse density modulation) which selects unique length sequences to give the same responsibility cycle but at higher frequency, at minimum for some gray values. A little bit improved, but there’s far more that can be finished.

Uncomplicated PWM vs lookup desk mapping

The factor is, our brains do odd items with the visual indicators we understand. Areas with the exact same gray worth, will be pulsating at the very same time, and the eye will be drawn to it and perceive flickering. So, the future trick was to check out to decouple nearby pixels in such regions using a LFSR sequence, which did give an apparent advancement. The actual aim was to check out to enjoy movie via the Lcd, so right after investigating spatial dithering, [Wenting] moved about to asking yourself if he could also dither in time, i.e. can the error in the time sequence be smoothed out in a identical fashion, to make the video clip seem far better? By utilizing a very simple sound-shaper, the video clip looked noticeably smoother, and practically flicker cost-free. Great final results! All in all, this is a extensive video to watch, but so crammed with handy tricks that it is in our view unquestionably worthy of your time.

We’re no strangers to driving retro displays with modern day hardware, for example CRTs, and while we’re contemplating about retro displays, how about this retro (and really disturbing) touch-enabled CRT from the early ’80s?

Many thanks [Philippe] for the tip!

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