[opendtv] Re: Philips ClearLCD technique for motion sharpness
- From: Doug McDonald <mcdonald@xxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 24 Jan 2005 16:46:31 -0600
jeroen.stessen@xxxxxxxxxxx wrote:
> Hello,
>
> Doug McDonald wrote:
>
>>I get the distinct impression that my LCD TV, a Panasonic
>>PT40LC12 RP-LCD set, refreshes at 300 Hz. It has a very
>>prnounced flicker at that frequency. Does anybody know
>>if this is really true?
>
>
> Most likely what you are seeing is the flickering of the backlight.
> A dimmable CCFL backlight often uses pulse width modulation for
> the dimming function, and it is not uncommon to use an odd multiple
> of the frame rate. (I can not explain why it should be odd..)
This set uses a high pressure mercury arc lamp. Jeroen ... are you
aware what "RP-LCD" means?
>
> It is interesting that your TV has that dimmable backlight...
My TV does have a dimmable lamp, however, it has only
two settings, 150 and 130 watts.
>
> The advantage of dimming is that it improves the black level,
> and it saves some power, of course. The disadvantage is that
> the whites will still be somewhat clipped. That would stop if
> you reduce the video gain instead. With a limited contrast
> ratio (white / black), typically 500:1 to 1000:1, you have to
> choose if you want better whites or better blacks.
Changing the lamp power has no effect on the contrast ratio.
It does have a substantial effect on the "purity", to use a
CRT term, of the screen. At the low power setting it is
much worse that at the high setting. At low power there
are faint green and pink colorations in some areas of the
screen in the 20 IRE area. This was fixed in the next
year's models.
Doug McDonald
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