[mythtv-users] HDTV Video Modes with MythTV

[James Oltman]

On 8/11/05, Hamish Moffatt <hamish at cloud.net.au> wrote:
> On Mon, Aug 01, 2005 at 11:53:16AM -0700, Brandon Rogers wrote:
> > At first, I thought the clarity of the 1080i (540p in
> > some cases) is actually better than the NTSC output.
> 
> Off-topic: I've noticed a few messages and sites that claim that 540p
> and 1080i are equivalent, and I can't understand how this is true.
> 
> They might be equivalent to the TV. In 1080i you send one set of 540
> lines followed by another which are displayed one line below. Repeat 30
> times per second (or 25 times in my case).
> 
> On 540p you send one set of 540 lines 60 times per second.
> The TV (needing to scale to 1080 lines, or thinking it's 1080i) will
> display every second set one line below the first set.
> 
> However in 1080i you have 1080 lines, updated 30 times per second.
> In 540p, you only have 540 lines! The resolution is halved, and it's
> not much more than 480i.


You are confusing frames, and fields.  In 1080i, you have 2 fields of
540 lines a piece.  The first field uses lines 1, 3, 5, etc all the
way to 539 or whatever.  The second field uses lines 2, 4, 6, 8 etc
all the way to 540.  Those two fields equal one frame of 1080i (i =
interlaced).  When you have 540p you are actually writing all 540
lines in both fields, thus making for a cleaner, smoother picture.  If
anyone can add/correct me, please chime in.  I am fairly certain that
is how this works.  It's been about a year since I played with HDTV
modelines.