Check out the research released publicly at Electronics Hacking: Creating a Strobe Backlight. If you have not read this up, you should read this very thoroughly, in order to understand what is going on.vturksoy wrote:I'll try to do hardware based, refresh syncronized strobing.
Read above. You must strobe only once per refresh.vturksoy wrote:I'll acsess to hardware and get signals from there and use it to strobe back light. I'll try this on a 65hz screen. More than 65 strobes for each refresh. Do you think that it might work?
Explanation Why You Must Strobe Only Once Per Refresh: As you track moving eyes on moving objects on a screen, your eyes are a different position at the beginning of a refresh than at the end of a refresh cycle. This creates the motion blur you see in the demonstration animation at http://www.testufo.com/eyetracking. Your eyes are continuously moving. But the frame is static for the whole refresh cycle. Your eyes are not digital stepper motors, so there's always a disconnect between your continually moving eyes (as you track moving objects on a screen) and the discrete stepping forward of a series of static images on a screen (e.g. series of refresh cycles). This creates the optical illusions you see at http://www.testufo.com/eyetracking (Tip: try the "Checkerboard" illusion). Eliminating this type of motion blur requires you to reduce the amount of time each frame is visible for, all the way from the first visibility of the same frame, to the last visibility of the same frame. So it is critically important, that you must make the frame visibility contiguously brief, aka one strobe per refresh, to minimize motion blur. You could flash multiple times in a short time period, but that would be a waste of brightness with a LED backlight; For efficiency's sake, might as well shine it contiguously for the whole target persistence, since strobed-LED and strobed-OLED persistence is equal to the time from the first visibility of a refresh to the last visibility of a refresh (And multiple strobes means persistence is effectively all the way from the beginning of the first strobe, to the end of the last strobe of the same refresh). If you strobe multiple times for the same frame/refresh while your eyes are moving (while tracking moving objects), your eyes will be in different positions during each strobe, and you get the dreaded multiple-image effect:
30fps@60Hz CRT, creates a double image effect
60fps@120Hz LightBoost creates a double image effect
60fps@180Hz PWM-dimming creates a triple image effect
etc.
EXAMPLE: View http://www.testufo.com on a CRT or LightBoost. You'll instantly understand why you want one strobe per frame.
Your LCD does NOT strobe by default.vturksoy wrote:on a 65hz LCD it strobes 65 times as default.
It's a continuously shining display, flicker free, strobe free, sample and hold.
See Understanding LCD Refresh Behavior Via High Speed Video.
It doesn't work that way. You must strobe only once per refresh. Read above.vturksoy wrote:it equals to 15.4ms motion blur. If I tweak it to strobe 130 times 7.7ms blur. if it strobes 260 times 3.8ms motion blur. 520strobes to 1.8ms motion blur. 1040 strobes to 0.9 ms motion bulur.
Light output of a strobe backlight (without overvoltage boosts, often found in LightBoost) is directly proportional to persistence.vturksoy wrote:My LCD is around 400 cd/m² so 325 strobes should give me 3ms presistance and fairly enough light.
So to reduce motion blur by 75%, you will be limited to 100cd/m2.
And to reduce motion blur by 90%, you will be limited to 40cd/m2.
Based on the CREE X-Lamp specifications, you can usually safely use approximately a 3x-5x overvoltage boost to create approximately 3x brightness, so you could theoretically get 120cd/m2 while eliminating 90% of motion blur.
One strobe per refresh. Read above.vturksoy wrote:Should I always multiply hz with X to have a proper strobe number? or can I set it to any value?
I do not recommend this. Efficiency of a backlight is extremely poor.vturksoy wrote:What if I remove the reflective surface on the back of the LCD and add more strobing leds on the back of the LCD ( a proper small box can be made with proper difusers to have even light.)
Instead, I recommend boost voltages instead, already found in a section of http://www.blurbusters.com/faq/creating ... -backlight
For your experiment I recommend a good target is approximately 80% motion blur elimination, which will give you 80cd/m2 out of 400cd/m2, then using boost to raise the 80cd/m2 back to 240cd/m2. This is still dramatic motion blur eliminaton on a smartphone, as it will suddenly look like a (65 x 5) = 325fps@325Hz motion clarity when viewing 65fps@65Hz scrolling at 1/5th persistence (1/5th of 1/65sec equals 1/325sec persistence, an 80% motion blur reduction -- using 65 strobe flashes of 1/325sec each, voltage-boosted to 3-5x wattage, for an approximately effective 240cd/m2 average brightness with 80% motion blur reduction.
"OPTIONAL (Advanced): Use boost voltage during flashes. If you have advanced knowledge of electronics, use boost pulses to overvolt the LED backlight so it flashes brighter during pulses. You will be able to gain at least 2x or 3x brightness, but with some accelerated wear and tear on the LED’s. Good study material for reading is CREE: Pulsed Over-Current Driving of Cree® XLamp® LEDs: Information and Cautions. LightBoost monitors actually also do this (albiet to a lesser extent) to compensate for the darkness between strobes, as discovered by Marc Repnow’s reverse engineering of LightBoost. Optionally, you can also add adjustable capacitor softening of strobes for CRT-style phosphor decay, to make the 60Hz flickering slightly less harsh.
Intensifying an edgelight is a lot easier than converting an edgelight to a backlight. However, I suggest the simpler voltage-boost method first, to see if you can get satisfactory performance. Remember, the 65Hz->"equivalence 325Hz" upgrade (even at 240cd/m2 voltage boosted) will be a much bigger upgrade than "60Hz->65Hz". You don't have to target ultrashort persistence such as 0.5ms or 1.0ms, when just merely having 3ms or 4ms persistence gives you the world's lowest-persistence smartphone.vturksoy wrote:Second plan is just to open reflective surface from led light side just enough to add another 12 set of leds with same specs. (double led row)
If you succeed in your modification, we'd love to feature you on Blur Busters. This talk is definitely "Area 51" worthy.