[mythtv-users] Always prescaling theme images on startup

Steven Adeff adeffs.mythtv at gmail.com
Tue Mar 20 17:45:32 UTC 2007

On 3/20/07, Phill Edwards <philledwards at gmail.com> wrote:
> > Although, note that if you prefer the scaling done by the TV and you run
> > X at 1280x720, you'll be using /both/ MythTV and the TV to do scaling of
> > video at any other resolution unless you also use XRandR (and don't mind
> > those annoying mode changes on your TV)...  Using both to scale should
> > be worse than using either one (if only one) to scale.
> Sorry to be dumb on this - I guess picture scaling is an area of
> MythTV I've never understood and I don't understand the implications
> of decisions I may make.
> My TV's best resolution is 1366 x 768 which isn't 16:9. I can't get a
> modeline that works at that resolution anyway, so I ended up going for
> 1280x768 which was the closest I could get. MythTV seems to like 4:3
> or 16:9 resolutions but that doesn't match my TV. So which to go with
> - the one that more closely matches my TV's native resolution, or the
> one that matches what MythTV likes? What impact on my viewing will my
> decision make - will I see a difference in picture quality or will it
> be so subtle that is just doesn't matter? And so what if both the TV
> and MythTV do some scaling - again, how will that affect viewing
> quality?

With regards to how MythTV *currently* does scaling...
Your best option is to send the signal to your HDTV in the original
format for that picture and let your HDTV do the scaling. 1080i as
1920x1080i or 1920x1080p, 720p as 1280x720p, SD as 480i/p (720x480).

The reasoning behind this is that your HDTV will have a better scaler
than MythTV does.

Once the work some of the devs are doing in the mythvid branch gets
merged, MythTV should have some very high quality scaling and
filtering, allowing for very high quality scaling of video to 720p or

> And is it a binary thing - the resolution is either bang on in which
> case no scaling required, or it's not in which case scaling is
> required (ie close just isn't good enough)?

more or less. depending on the technology your tv uses. LCDs and
plasma invariable use an oddball resolution natively which means no
matter what signal your sending them they scale. For smaller TV's
(under ~50") the outcome of scaling between 1080i and 720p is
negligable (though for SD to 720p can be quite noticeable).

Many of the newer 1080p LCD/plasma screens have 1920x1080p natively,
some though have a resolution between 1366x768 and 1920x1080, so they
scale everything as well. That doesn't mean they will look bad. If
Sharp made an Aquos at 1600x1200 and sold it as 1080p it would most
likely look better than a cheaper display element at true 1080p.

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