[mythtv] ffmpeg SWSCALE!

Michael T. Dean mtdean at thirdcontact.com
Thu Aug 31 01:03:53 UTC 2006

On 08/30/06 19:12, Steven Adeff wrote:

>On 8/30/06, Michael T. Dean <mtdean at thirdcontact.com> wrote:
>>But, if done right, DVD's in 720x480 anamorphic widescreen on a 1080p TV
>>can give nearly the same quality output as HDTV in 1080i/p on a 1080p TV...
>rotfl! thats because all you've see is broadcast 1080i, which does not
>come close to image quality that HD-DVD provides. HD-DVD, on a true
>1080p display will blow. your. mind. Its truely a site to behold, even
>PBS/InHD/HDNet can't come close to the bitrate and color palette that
>HD-DVD will provide. HD-DVD also has the honor of holding uncompressed
>surround sound. Where DVD's are AC3/DTS encodings (of usually
>processed) theatre audio, HD-DVD will hold the uncompressed audio (and
>from what I understand, unprocessed from what I hear as well.
>You just can't "make up" the information by upsampling.

True, but if you're processing the images correctly, you're not making 
up information (nor are you "upsampling"--i.e. 1 pixel becomes 4 or 9 or 
whatever).  Notice, however, the, "If done right," in my original statement.

A digital image defines a set of samples, which can be displayed as is 
(i.e. a 1:1 pixel mapping) to /approximate/ the original image, or can 
be used with a proper reconstruction algorithm to recreate the original 
image /function/ from which the samples were taken (where the image 
function is a continuously-defined function, as opposed to the digital 
samples in the image itself).  If the image function is recreated, it's 
possible to resample the function for the desired number of pixels.  In 
doing so, no information is "made up"--instead, the information that's 
encoded into the original samples is just better applied.

And, as mentioned in reply to your post in the thread, "Graphics card 
recomendation" ( 
http://www.gossamer-threads.com/lists/mythtv/users/220344#220344 --mine 
will appear somewhere below there once the archive catches it), a 
display device needs at least 2x the pixels on each axis to fully 
represent the information in a given image.  So, a 720x480 DVD needs at 
least 1440x960 pixels.  And, a 720p TV has 1280x720 pixels, so you'd 
need a 1080p TV (with 1920x1280 pixels) to fully appreciate the images 
on the DVD.

(BTW, the reply in the other thread is one which your laughter prompted 
me to actually send, after it sat in my Drafts folder for a day and a half.)

In the real world, it's impossible to recreate the image function 
exactly from the samples that are taken--primarily because in the real 
world, signals are rarely band-limited.  Nonetheless, there is 
additional information in the image that can be extracted through an 
appropriate reconstruction process (and can result in a much better 
image given 4x the pixels for output).  Once you've reached a 
sufficiently-higher resolution than the image resolution (somewhere 
around 2x the pixels in each dimension), you will no longer see an 
improvement in picture quality.  At this resolution, you've used all the 
available information in the signal and eventually you will begin to 
bring out the artifacts/aliasing in the image.  But, as mentioned, 
1920x1080 works quite well for DVD's...

Besides, if you're talking about replacing DVD's with HD-DVD's, 
depending on the source, the studio may be "making up" as much 
information as the player that decodes the DVD.


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