From: Benjamin Koh (koh_benjamin_at_hotmail.com)
Date: Wed Sep 01 1999 - 03:46:01 EDT
Jeff,
I think the reason stems from the way LCD screens are constructed
differently from CRT monitors. Read on, and it should be clear that there's
nothing you can do about this.
Unlike in conventional CRT monitors where 3 dots of red, green and blue
converge to form white, in a LCD screen the white comes from the human eye
averaging three distinct subpixels of red, green and blue that are placed
very close together. The subpixels that make up each pixel all go
red/green/blue. Each subpixel is a third the height of a normal pixel so
when stacked vertically they form a "normal" pixel. To avoid the eye
perceiving the nice horizontal lines that this would generate, each
subsequent column is shifted by one pixel, so the second column goes
blue/green/red and the third goes green/red/blue. This is reading the
subpixels from top to bottom. Look at the "sets" I've drawn below. It may
make it clearer.
rgbrgbrgbrgbrgbrgbrgbrgbr } one
gbrgbrgbrgbrgbrgbrgbrgbrg } row of
brgbrgbrgbrgbrgbrgbrgbrgb } pixels
|
V
(One pixel)
When you set the colour to magenta, you turn on all the red and blue
subpixels but not the green ones. The top left subpixel is red but it's
separated from the blue subpixel by the green subpixel which is off. Thus
there is a black subpixel between the red and blue. The pixel next to it
starts green/blue/red, so the blended magenta color is also separated from
the top left subpixel by a green subpixel that is off. Result: the red
subpixel appears as an individual pixel. The other red/blue subpixel sets do
not suffer this because all of the other red subpixels have 2 or more blue
subpixels in the vicinity. Only the very first red subpixel is surrounded by
only 1 blue subpixel in its lower right edge, so it appears less blue than
the others. Thus it appears red.
The TP 600 screen resolution is 1024x768. 1024 when divided by 3 leaves a
remainder of 1 so the last pixel in row 768 is also the same as the first:
red/green/blue. For the same reasons I have outlined earlier, it appears
blue and not red/blue (magenta).
I hope this clears up your queries.
You can also turn the screen green (0, 255, 0) and take a magnifying glass
to the corners. The top left and bottom right corners should show a small
indentation, like a square cut out of them.
This will be true of all color LCDs. The artifacts may vary in the corners
they're located in if the first pixel is green/blue/red for example. If it
was green/blue/red then a yellow screen would give a green artifact in the
top left corner. Obviously this will not work on CRT monitors since there
are no real pixels - just fuzzy bits of light blended together.
I have a feeling I may have overdone the explanation :-)
Cheers
Benjamin
>From: Jeff Macht <jamacht_at_home.com>
>Reply-To: Jeff Macht <jamacht_at_pobox.com>
>To: thinkpad_at_cs.utk.edu
>Subject: Thinkpad 600E LCD color -> What's up?
>Date: Tue, 31 Aug 1999 21:56:03 -0700 (PDT)
>
>Can anyone with a 600E try this out? I have a 2645-5AU so anything similar
>would be cool.
>
>Change the background colour in Windows 98 to the color
>(R,G,B)=(256,0,256), which is magenta. Now look at the left and right
>edges of the screen. Is the last pixel (on the left) red or (on the right)
>blue? That's what I get. If so, what is the reason for this?
>
>If you set the background to pure red or blue, the left or right
>respective single pixels are black.
>
>Is this a software (driver) or hardware issue that i'm having? Or should I
>just ignore it? It's hard to ignore once you see it.
>
>Thanks in advance for anyone noting the same problem,
>
>Jeff.
>
>--
> Jeff Macht (jamacht_at_pobox.com) |"Dreams become reality when desire
> http://www.pobox.com/~jamacht/ | transforms them into concrete action",
> NeXT Mail, MIME accepted | Gus, from the film The Top of his Head.
>
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