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

Oded Shimon ods15 at ods15.dyndns.org
Thu Jun 30 18:06:10 CEST 2005

On Thu, Jun 30, 2005 at 08:55:09AM -0700, Loren Merritt wrote:
> 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.

This is nonsense. (hmm, i'm starting to talk like Rich.. :) The entire
monitor is completely BLACK, _except_ for the horizantel line it's drawing.
There's no "mixture of 2 images", because there's no micture at all. The
monitor shows a line, the line is "burned" into your eye, remembered, then
the line disappears. _immedeately_. and so on for the next line, until the
entire picture has been burned into your eye, and then the monitor moves on
to the next image, by that time your eye has "recovered" from it's burn and
is ready for the next 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,

No, it's 2 images, and it's really not even that. it's the top half being 
the first frame (In your eye! the monitor is completely black ofcourse, as 
always), and the bottom half being the new frame.

> with one of the 
> boundaries staying still for 1/75 second or so, which is long enough to 
> notice.
> --Loren Merritt

- ods15

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