Half D1?

[backpages]

Could someone please explain to me or direct me to an explanation on the web of Half D1 works? If the resolution is only 352x480 why and how does it fill up the entire TV screen? 352x480 would provide a "vertical" image, so how does it end up being a "horizontal" or 4:3 image? Thanks for any insight or help. Steve

[Abond]

Magic...

You are in breach of the forum rules and are being issued with a formal warning. While "smart" remarks are sometimes ignored (sometimes even quite amusing), it's just bad taste for it to be the first reply to an otherwise serious post. Either try to help, or don't post at all. It's not like the poster had asked a stupid question (like "can I turn my CD burner into a DVD burner"). What he asked is neither common sense, nor readily explained anywhere.
/ Moderator lordsmurf

[lordsmurf]

The pixels are not 1:1 square, but rather 4:3 rectangle shaped. In fact, 720x480 is not stored as 1:1 data either. It too, is 4:3, otherwise it would appear to be "too long" or "too wide".

https://www.videohelp.com/glossary?H#Half%20D1

VHS is very much similar, it has a resolution (well, sort of, I'm referring to digital equiv here mostly) closer to about 250-350x480. It's somewhat less than even 352 would be.

[backpages]

Thanks for the info.

[Abond]

Your player "stretch" the image horizontally so it will fill the entire screen. In the firmware there is (probably) an algorithm to stretch valid DVD resolutions horizontaly and also verticaly (352x240 for example). New models provide more flexibility at this point. An year ago there were players not able to stretch properly SVCD resolution.
BTW this stretching give blurier image (because there is no information available - only for 352 pixels). This ofcourse reflect to image quality.
This is what I think about. But how in details it is done - pure magic.

[backpages]

Cool, thanks, this helps.

[Cornucopia]

MPEG2 stream makes note of PAR (pixel aspect ratio) and DAR (display aspect ratio). Preference is given to DAR. (Sometimes PAR isn't even listed/editable)

If DAR = 4:3,

640x480 NTSC --> PAR = 1:1 (square)
720x480 NTSC (DVD) --> PAR = 1.125:1 (narrow pixels)
unless overscanned, then 1.1:1
704x480 NTSC (DVD/D1) --> PAR = 1.1:1 (narrow pixels)
480x480 NTSC (SVCD, 2/3D1) --> PAR = .75:1 (wide pixels)
352x480 NTSC (1/2 D1) --> PAR = .55:1 (wide pixels)
352x240 NTSC (VCD, 1/4 D1) --> PAR = 1.1:1 (narrow pixels, just 704)

Similar things happen to PAL, although those are almost always wide.
(Just mentioning NTSC here 'cuz that's what was posted)

Scott

[lumis]

not to highjack this thread, but its in a similar vein.

is it possible to have anamorphic widescreen half D1 video?

[lordsmurf]

is it possible to have anamorphic widescreen half D1 video?

There is not a real good reason for it NOT to work, but the hardware and spec does not seem to include it.

[Cornucopia]

Generic MPEG2 1/2D1 for use on PC--yes, DVD 1/2D1--NO.

Acc'd to the spec, only 720x and 704x support anamorphic widescreen.

Scott

[Gurm]

Furthermore, your TV is analogue. It just displays what it's given. If the player chooses to declare that 352 is an entire scanline, the TV just shows it as such. On your computer, there's an upsampling algorithm. On the DVD player, it just declares that those 352 pixels are the entire scanline and is done with it.

Note that your TV's actual "resolution" is actually quite low (normal consumer-level TV's here, not high-def or widescreen units) - somewhere around 400x400 depending on the model. But that's a bad term anyway, when referring to a device which only accepts an interlaced analogue signal.

[edDV]

Furthermore, your TV is analogue. It just displays what it's given. If the player chooses to declare that 352 is an entire scanline, the TV just shows it as such. On your computer, there's an upsampling algorithm. On the DVD player, it just declares that those 352 pixels are the entire scanline and is done with it.

Note that your TV's actual "resolution" is actually quite low (normal consumer-level TV's here, not high-def or widescreen units) - somewhere around 400x400 depending on the model. But that's a bad term anyway, when referring to a device which only accepts an interlaced analogue signal.

If the TV (NTSC) doesn't have a comb filter, luminance is filtered out around 3MHz for ~240x480 (analog "lines of resolution") approx 330-352x480 in digital pixel speak.

That's for the tuner section. An S-Video input may avoid the evil 3MHz luminance filter and allow display at the limits of the TV CRT.