Re: White point for LCD
Re: White point for LCD
- Subject: Re: White point for LCD
- From: William Hollingworth <email@hidden>
- Date: Thu, 19 May 2005 14:22:35 -0500
For a standard CCFL based LCD monitor, the only way to change the white
point of the display aside from using LUTs on the host PC, is to modify the
video going to the panel itself.
Typically this can be done in internally to the monitor using either:
1. Scale the input video using an internal "gain control". In simple terms
you just multiply each incoming video level by a scale factor (gain). The
bad point about this is that as you change the gain, you also change the
shape of the display's response curve.
2. Scale the video by using an internal LUT and a color processor with
knowledge of the LCD panel's native response characteristics. This will
maintain the shape of the display's response curve as the "gains" are adjusted.
Low end LCDs would typically use 1., and higher end LCDs typically use 2.
With either option, the more you change the white point away from the
display's native white point, the more displayable levels you loose in the
process. That is why there is a need for 10 bit LUTs and true 10 bit LCD
panels.
Another negative point about white point adjustment on CCFL based LCD
monitors is that while you can scale the white point, the black point
"color" is essentially fixed (as determined by the color of whatever light
leaks from the LCD panel itself with a (0,0,0) video input. So your
greyscale tracking from white down to black can be less than optimal,
depending on the white point selected.
The upcoming NEC LCD2180WG LED based wide color gamut display uses
individual red, green and blue LEDs as the backlight source. The intensity
of each LED color can be controlled individually so the display's white
point can be adjusted without having to modify the display's internal or
host PC's LUTs. That means that:
1. The full resolution of the display's 10 bit LUT and the LCD panel is
utilized.
2. The black point of the display will also vary with the white point setting.
3. The host PC's internal LUTs can be set to linear - so the maximum use of
the 8 bit output from the PC is made.
Will Hollingworth
Manager of OEM Product Design & Development Engineering
NEC Display Solutions of America, Inc.
http://www.necdisplay.com
At Wed, 18 May 2005 17:37:17, Roger Breton <email@hidden> wrote:
> The Eizos (many of them not just the ColorEdge series) have adjustable
> color temp also. The adjustment is not accomplished with a graphic card
> LUT adjustment as the adjustment is made from the monitor. The question
> of "how" still exists though. Doesn't the monitor have a LUT of it own,
> hence the "14 bit" and "10 bit" internal LUT claims? I agree with your
> premiss that you can't vary the color of the actual light output as
> there is only a single source. It must change the appearance of the
> white point by altering the color of all pixels.
>
> David
I'd like to know the answer of that one too. Maybe someone from Eizo
monitoring the list could do everyone a favor by explaining how this is
done? If this is not a commercial secret.
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