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HDTV Aspect

HDTV versus SDTV(NTSC) Screen Size

For a new TV, should I buy a wide HDTV screen or a Standard TV (STD) / NTSC screen?

What size screen should I buy?

While I can't make the decision for you, here is some simple math to help you get a handle on the screen size for HDTV versus NTSC.

Reminder: Pythagorean Theorem is a^2 + b^2 = c^2 for right triangles

NTSC aspect ratio is 4:3, forming a 3:4:5 right triangle with diagonal 5.

HDTV aspect ratio is 16:9, the diagonal is SQRT(337) = 18.358

HDTV Aspect Ratio

Scale factor from NTSC diagonal to needed HDTV diagonal [NTSC upgrade to HDTV]

1.224 = 337^0.5/15
When upgrading from NTSC to HDTV, use the above scale factor to convert your current NTSC TV diagonal to a HDTV diagonal that will show the same size NTSC image as your old NTSC TV.

Scale factor from NTSC diagonal to viewable HDTV diagonal [NTSC displaying HDTV signal]

0.918 = 337^0.5/20 = 337^0.5*(3/4)/15
Use the above scale factor to go from your NTSC TV diagonal to the displayable HDTV diagonal.

Scale factor from HDTV diagonal to viewable NTSC diagonal [HDTV displaying NTSC signal]

0.817 = 15/337^0.5
Use the above scale factor to go from your HDTV diagonal to the displayable NTSC diagonal.

Empty area

Empty area on HDTV screen viewing full-height NTSC image
¼
Empty area on NTSC screen viewing full-width HDTV image
¼

Interestingly enough, the blank area on the screan is 1/4 for either a NTSC TV or an HDTV viewing the other signal.

Here's a handy graph so that you can read off the conversion that you need.


Discussion

To answer the original questions, I highly recommend buying a wide screen HDTV for the following reasons.
  1. The "industry" has standardized on HDTV and has committed to the format for the future.  While the migration is somewhat slow due to various factors, it is progressing.
  2. Wide screen aspect matches both HDTV and DVD movies, and both of these signals have more resolution than NTSC.  So it is better to have the bigger (area) image for the higher resolution HDTV or DVD material, with the smaller (area) image for lower resolution NTSC programming.
  3. HDTV is a must have.  Once you have seen HDTV, you won't want to go back to SDTV/NTSC.  Are you a sports fan?  Many games are already being broadcast in HDTV.
  4. HDTV recordings will come.  Right now, you have to do your own recording using something like a HDTV HTPC.  But keep an eye out for HDTV on DVD.
Use the "NTSC upgrade to HDTV 1.224" factor to convert from a current NTSC TV to a diagonal for an HDTV that will show the same size NTSC image.