Archived from groups: alt.comp.periphs.scanner (
More info?)
"Kennedy McEwen" <rkm@nospam.demon.co.uk> wrote in message
news:QiYqx$BBK+fCFwqe@kennedym.demon.co.uk...
In article <jArfe.60$aM4.32@newssvr11.news.prodigy.com>, CSM1
<nomoremail@nomail.com> writes
>
>USA HDTV is Maximum 1920 x 1080 pixels. Aspect ratio is 16:9.
>USA Standard Definition TV is Max Resolution of 720 x 486 pixels, the
>common
>use size is 640 X 480 pixels. Aspect ratio is 4:3.
>PAL is 576 x 720 pixels. Aspect ratio is 5:4.
>
>http://www.ee.surrey.ac.uk/Contrib/WorldTV/digital.html
>
Careful! Both PAL and NTSC have aspect ratios of 4:3!
The 720 horizontal resolution in standard TV (both PAL and NTSC) is a
fudge of the transmission mode (nice integers of the chroma subcarrier
subsequently encoded on the data for transmission) which is only
achievable with the use of non-square pixels - something that computer
graphics and scanners generally avoid.
If you scan at 720x486 for NTSC or 720x576 for PAL using a standard
scanner and then display on those media you will end up with distorted
images. The final images will appear 6.7% too wide in PAL: somewhat
less than watching standard 4:3 images on a widescreen TV (which seems
as acceptable to the fast majority of gogglebox addicts as a vain
politician telling them they will be blown up in 45 minutes by a feeble
middle east dictator) but is clearly visible and objectionable to anyone
expecting a factual representation of the real world.
The correct image resolution for 4:3 PAL (ie. the answer to the question
asked) is 768x576 pixels, best achieved by scanning at an integer
multiple of these values (eg. 1536x1152 or 2304x1728) and then
downsampling to 768x576 using an algorithm that efficiently retains
image content but avoids aliasing. For 16:9 PAL, aim for a final
resolution of 1024x576 square pixels.
If you must use the 720 horizontal pixel standard (for example if your
DVD player does not offer a square pixel setting for still image replay)
then resample to that resolution from your scanned 4:3 aspect *whilst*
changing the image aspect ratio to 5:4. The video system will then
stretch this back to a 4:3 aspect by using non-square pixels. DO NOT
SCAN THE ORIGINAL WORK AT A 5:4 ASPECT RATIO!! (This will effectively
double the distortion).
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a ah heck when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
Kennedy,
Thanks for your comprehensive reply.
Beemer
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