You say "They stay lit only as long as the sustain pulses are applied to the row drivers." Is there not a persistence factor wrt the phosphors? Not quite truly binary...but almost.
On 12/4/2009 9:05 AM, Stessen, Jeroen wrote:
Hello,Kilroy Hughes wrote:Ø Most new TVs do a good job of inverse telecine, where they throw away the repeat fields,Ø reconstruct the original 24p capture, and preferably blink it 5 or 10 times (called 120Hz orØ 240Hz "refresh" ... as though LCDs and plasmas don't stay lit or something.Ø Apparently it has to do with some ancient ritual involving electron beams.). Plasma panels don't stay lit anymore than CRTs do. They stay lit only as long as thesustain pulses are applied to the row drivers. And as they are inherently binary, thebrightness of each pixel must be pulse-code modulated. This is done by lighting uppixels during sub-fields with different duration, for different weight factors per bit. Soit's very common for a plasma panel to operate at 600 sub-fields per second, "600 Hz".Panasonic even seems to manage to apply separate motion compensation to each sub-field. This may reduce the false contour artefact, where due to eye tracking the sub-fields for different objects are combined on the retina into the wrong brightness values.LCD is different. It is a light valve, that (in the absence of black field insertion) is alwayson. Also the backlight (in the absence of backlight scanning) is always on. In principle itis possible to refresh an LCD as slowly as 24 frames per second (although that doescreate a problem for the polarity inversion, which we don't like to be at 12 Hz). But ifwe do that then we get a serious problem with the motion portrayal. Such display putsmoving objects at a new position every 42 ms, and then keeps it there for the remainderof the period. Eye tracking is continuous, so this means that the object is now smearedover the retina (convoluted) by a temporal aperture of 42 ms. This makes that movingobjects will be very unsharp. Increasing the frame rate (to 60, 120, 240 Hz) andrepeating the frames (2.5, 5, 10 times) changes exactly nothing. The only thing that isworse is 3:2 pull-down, where one frame is repeated 3 times and the other 2 times.this creates 12 Hz motion judder (and 5 displaced images) on top of the 24 Hz problem.The real solution, and all TV manufacturers are applying this, is to do motion estimationand motion-compensated frame rate up-conversion. This puts the moving objects inthe correct spatial position in the interpolated frames, so that there will be much lesssmear on the retina of the tracking eye. There still remains motion blur due to theshutter time (temporal aperture) of the camera, which is typically around 10 ms.Thus there is little benefit in reducing the display hold time below 10 ms (100-120 Hz).Still, companies like Samsung are promoting 200-480 Hz technology. This can only bedemonstrated with synthetically generated moving images, with no camera blur.The interpolated frames do not necessarily have to be motion-compensated, they mayalso be black. Then it's called black field insertion and/or scanning backlight. The CRTwith its short phosphor decay time had exactly the same advantage. The price to pay isflicker, so the illuminated frames should still occur at 72 Hz or faster (i.e. 100-120 Hz).It is not uncommon to call a 100 Hz display with a 50% (duty cycle) scanning backlighta "200 Hz display", because they have the same 5 ms temporal aperture. Actually, the100 Hz display with inserted black is probably better, because interpolated frames aregenerally of lesser quality than original frames or black frames.A good TV with 100-600 Hz motion-compensated frame rate will have a much bettermotion portrayal than a cinema, where frames are repeated 2-3 (or 6) times withoutmotion compensation. That gives judder and multiple images on the tracking retina.But then you lose that "film look" on the TV. Duh !Kilroy, you ought to know better. You were there when Dave Marsh and John Watkinson published their excellent whitepapers through Microsoft: http://www.microsoft.com/whdc/archive/temprate.mspx http://www.microsoft.com/whdc/archive/convrg1.mspxA story about display frame rates of 120 Hz or higher would not be complete withoutmentioning that such displays are thought to be ready for field-sequential 3D. This iswhere the display shows the left-eye and right-eye images alternately, and a pair ofactive (LCD) shutter glasses blocks the other eye. It is a cheap way of making a3D-ready display, if you don't mind the high price of the glasses. This is easily realizedwith DLP (digital cinema !) or plasma displays, and much less easily with LCDs(because in spite of the high frame rates their response time is way too slow).Groeten, -- JeroenJeroen H. 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