[MPlayer-DOCS] [PATCH] DOCS/tech/tearing.txt

Loren Merritt lorenm at u.washington.edu
Thu Jun 30 17:55:09 CEST 2005

On Thu, 30 Jun 2005, Diego Biurrun wrote:
> On Tue, Mar 08, 2005 at 12:07:23AM +0100, Diego Biurrun wrote:
>> On Mon, Mar 07, 2005 at 04:44:21PM +0200, Oded Shimon wrote:
>>> What happens with tearing is that halfway through this process, the
>>> image changes - a very likely event. Because of this, the monitor
>>> displays the first half the first image, and the next half it shows the
>>> new image, thinking it's all the same image. The mistake will be
>>> "corrected" in the very next refresh, as then the entire screen will be
>>> the new image - too slow. Our eye already caught the mistake. With
>>> extremely high refresh rates (150hz+), tearing is practically
>>> unnoticeable.
>> I'm not particularly fond of this paragraph.  It could be slightly clearer.
>> Sorry for not being more specific right now..
> I must admit I don't get the above paragraph 100%, can somebody
> elaborate?  Rich?

A CRT doesn't display a whole image at once. It updates one row, and then 
the next row, and so one until the bottom of the screen, and then jumps 
back to the top ("v-sync") and continues. So at any instant, the top 
portional of the screen is from one image, and the bottom portion is from 
the previous image. As long as the image being display only changes during 
v-sync, you don't normally notice this, because the border between the two 
images is moving really fast. However, if you change the display part way 
through the scan, then it's a mixture of 3 images, with one of the 
boundaries staying still for 1/75 second or so, which is long enough to 

--Loren Merritt

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