An XOR gate and inverter computes the next bit of the sequence by XNOR’ing two feedback bits taken from taps on the register, and this bit is then fed into bit zero. The core of the project is a 242-bit linear-feedback shift register (LFSR) constructed from (31) 74LS164’s. Of course, the components used will fail long before the sequence repeats, but who cares, this thing looks awesome! Check out the gorgeous wire-wrapping job! When lucked into a bunch of 5 mm red LEDs and a tube of 74LS164 shift registers, a project sprang to mind: “The Forever Number,” a pseudo-random number generator with a period longer than the age of the universe. Continue reading “Monochrome LCD Video Hacks Galore!” → Posted in Video Hacks Tagged dithering, error diffusion, lcd, LFSR, PDM, pwm Slightly better, but there’s more that can be done. One way to mitigate that is to switch to PDM (pulse density modulation) which selects different length sequences to give the same duty cycle but at higher frequency, at least for some grey values. But, that gives a worst case effective refresh rate of 8 Hz with a PWM period of 15 frames, at 120 fps, and that flickers. The next idea is to PWM the individual pixels over multiple frames, to approximate different grey levels. But, the pixels themselves are still either on or off. This error diffusion process smears the error out over the whole display, so spatially speaking, on average the pixel values correspond roughly to the original gray values.
The resulting error value, is then propagated to neighbouring pixels. For each pixel, it is set to black if the grey value is below some threshold. The first idea is to use a traditional dithering technique. goes through multiple techniques, showing the resulting image quality in a clear, systematic manner.
But, what if you have a monochrome-only display controller? With a sufficiently high pixel clock, can you use software on the application side of things to flip those pixels in such a manner as to give a reasonable looking grayscale image? Simple dithering – don’t look too close! PDM greyscale approximation in a 1-bit display If the display controller supports multiple bits per pixel, it can use various techniques, such as PWM, in order to produce a pseudo-grayscale image. Is clearly a fan of old school STN LCD displays, and was wondering how various older portable devices managed to drive monochrome LCDs panels with multiple grey levels.
0 kommentar(er)
