[mythtv] bobdeint observation

John Patrick Poet john at BlueSkyTours.com
Wed Sep 1 21:57:44 EDT 2004


Doug Larrick wrote:

> Isaac Richards wrote:
>
>> On Saturday 28 August 2004 01:17 am, Andy McMullan wrote:
>>
>>> Basically all this does is draw the second field one pixel lower than
>>> the first field. The effect is pretty subtle, but I'm pretty sure it
>>> gives a better result.
>>
>>
>> I've had this (well, same idea) in my tree for a couple weeks now.  
>> It does actually make video playback look very good on my (ntsc, 
>> fx5200) tv-out, but the OSD still looks bad.  Haven't had time to 
>> mess with it much, though.
>
>
> The attached patch seems to get it right for both top-first and 
> bottom-first videos for me.  For HDTV, it doesn't seem to make much 
> difference since the fields are so big to begin with.  But for 
> standard-def stuff it does make a difference.
>
> The reason the OSD looks bad is that it's being drawn onto a surface 
> with only half the normal vertical resolution (one field).  In order 
> to make it look nice, you'd have to do one of:
> * double the scanlines in software into a full-height Xv buffer before 
> rendering the OSD onto it
> * arrange for the filter to output two full-height frames rather than 
> the current way of using the top half for the top field and the bottom 
> half for the bottom field.  I avoided this approach to keep from 
> complicating the filter interface; doing so, though, would allow 
> adoption of some of the more advanced deinterlace filters from e.g. 
> TvTime
> * figure out how to render the OSD in an interlaced manner, sending 
> the appropriate OSD scanlines to the appropriate fields in the video.
>
> -Doug


I briefly had a PVR-350 in my system.  Video quality was poor compared 
to my old ReplayTVs.  Tried this patch and it made a very nice 
improvement.  I can recommend this patch to those using PVR-x50 cards.

John



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