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Thinkpad T60P LCD barrel pincushion distortion ???
Posted: Sat Jan 26, 2008 9:13 pm
by devnull
Hello,
This may sound odd and even unheard. I recently swapped my Thinkpad T60p 15" LCD display from SXGA+ to UXGA. Everything was fine.
But today I notice barrel and pincushion distortion, by about 3 pixels on all 4 sides. I am aware such a thing is uncommon in LCDs, but it is the case. I am very sure that display was not distorted when I sewed it together. The only thing I did was to keep the machine running for almost 3 days. I checked the LCD bezel to see if its skewed, but it doesn't look like either.
Any clue on what could cause this!
Thinkpad T60P LCD barrel distortion ???
Posted: Sat Jan 26, 2008 9:16 pm
by devnull
Sorry, I made a mistake. I meant barrel distortion, not pincushion.
Posted: Sat Jan 26, 2008 9:53 pm
by sjthinkpader
Over the TFT array is a color filter. They are made separately by different companies then aligned together by a machine. So there is no barrel or pin cushion distortion there.
The array is driven by a decoded/controller on the LCD assembly. It drives the row and columns by column and row drivers. So there cannot be any barrel and pin cushion distortion here either.
The video controller sends pixel data to the LCD controller via interface called LVDS (low voltage differential signaling, precursor to DVI). This interface is digital and may or may not be row oriented.
So are you sure this is not your eyes or eyeglasses?
How do you know it is 3-4 pixels? Are you looking at it with a loupe?
Posted: Sat Jan 26, 2008 10:32 pm
by devnull
Thanks sjthinkpader!
My eyes indeed
The culprit is the LCD bezel. It is pincushioned, which is making the LCD appear barrel shaped. I kept a linear object along the inner borders and the centers on all 4 sides of the bezel are drawn inside making the appearance geometrically distorted.
Well, mystery resolved, case closed!
Posted: Sat Jan 26, 2008 11:10 pm
by sjthinkpader
Great,
This could be possible with LCD monitors using analog VGA interface. The computer sends not pixel data but line scan. So they are not pixel accurate. When you look at objects on the screen with a loupe, it will not have that crisp pixel border. But the LCD on our Thinkpads are pixel accurate.
Having perfectly straight lines are actually not natural in our world. But it is easier to manufacturer and standardize. Designer don't like to use straight lines unless they are forced to, by economics. Engineers use straight lines due to simplicity.