TV resolution encoding

[hassegubben]

I'm always watching my encoded movies on TV. What would be the best resolution for the most crisp picture so the TV don't have to resize and thus blur the image? Is 720*xxx better than 640*xxx? My TV is a widescreen with auto full screen resizing.

[scharfis_brain]

a TV cannot resize a picture and thus it cannot blur the image through resizing.
the "resizing", that your TV applies is only a modification of the timings, that guide the electron-ray (elektronenstrahl, don't know this word..) over your TV-screen.

It is always the Player (SAP/TV-Out) that resizes the image.
please tell me, what you're using (TV-Out/SAP)

[SeeMoreDigital]

Originally posted by hassegubben
I'm always watching my encoded movies on TV. What would be the best resolution for the most crisp picture so the TV don't have to resize and thus blur the image? Is 720*xxx better than 640*xxx? My TV is a widescreen with auto full screen resizing. I have a widescreen TV and I personally use an image pixel frame size of 720x576 (Im in a PAL country)!

While 'resizing' an moving image should not produce motion blur, it can introduce 'softening'. Afterall, there's only so far a pixel can be stretched. And some viewers have a more forgiving eye than others. So 'resizing' is another one of those 'personal preference' type discussions!

What ever you decide to do when 'encoding' your images, it's an established fact that, when playing them back on your widescren TV, you should not use your TV's 'AR' (resizing) button to stretch the image vertically. As this introduces very visable horizontal lines.

If you are using a graphics card with TV output, it's far to say that some cards are better at puking out a TV image than others. This is why I use an Sigma Xcard!

Cheers

[hassegubben]

I'm using a Philips TV 32PW9617 and a first generation geforce tv out(ASUS deluxe something...) and I DO get black horisontal stripes all over the picture. Is that because of the TV auto stretch function? I want as crisp picture as possible-would that lead me into Quarter pixel and full resolution? Would using TVtool(a must, to get the picture to the TV) render a better stripe free, full TV picture?

[SeeMoreDigital]

The Philips range of TV's have very good 'auto adjust'!

However, when you generate an encode for specific viewing on a widescreen TV you have to make sure that you encode in 1:1 (anamorphic) mode and that the encoded image pixel frame size is 720x576/480!

Your finished encoded image should look all 'squashed up' when played back and viewed on a PC's (4:3) monitor (this does not mean to say you can't view it correctly on a PC monitor) but when played back and viewed on a widescreen TV it should look correct!

I may be worth pointing out that when generating encodes for specific viewing on a TV monitor (instead of a PC monitor) you can reduce the bitrate quite a bit too. That said anything over 1000kbps looks excellent. But even at around 600kbps it still looks way better than VHS tape!

Cheers

[hassegubben]

@SeeMoreDigital:I figured a television set didn't show all 720 lines and that some were hidden and used for text content. The actual number of lines on screen would be less than 720, hence my consern. Then i believed the actual number of lines viewed on the screen would be the corresponding number of pixels (<720) to encode at. Is that wrong?

[hassegubben]

I'm correcting my mistake:The TV shows 480 out of 525 lines, so what I really meant to ask-does one pixel height roughly correspond to one line on the TV? Or is it better to always aim for full resolution when encoding for TV?

[SeeMoreDigital]

Hi hassegubben

Could I begin in asking you, were you are in the world. Are you a PAL DVD/TV user or an NTSC DVD/TV user?

When you see the expression 720x480 or 720x576. 720 refers to the 'width' quantity of pixels. And 480 or 576 refers to 'height' quantity of pixels.

NTSC DVD's are encoded using an image pixel frame size (resolution) of 720x480.
PAL DVD's are encoded using an image pixel frame size (resolution) of 720x576.

As a general rule, the more vertical pixels you encode with, the better looking the image. However, it's pretty pointless exceeding the vertical resolution of the 'source' DVD.

So if you are an PAL DVD/TV user, your DVD player will output 576 vertical pixels and your TV will display 625 vertical lines. (Setting the screen resolution of a PC monitor is a different affair, as you are able to set the screen resolution in pixels, which are far higher than a DVD's pixel resolution).

One important thing DVD encoders must understand is that the images are stored on the disc 'anamorphicly' using square pixels.

The definition of the word 'anamorphic' means: - "a distorted image which appears normal when viewed". Which in the case of a PAL DVD, means that the images are squashed up at a ratio of 1.25:1 (720/576 = 1.25:1).

So in order for you to view a DVD image correctly on your TV, each pixel has to be stretched 'anamorphicly' horizontally. This is done by visiting the setup options of your DVD player and setting the correct TV's screen shape (4:3 or 16:9).

And please don't confuse the DVD's 'anamorphic' ratio with the movies image aspect ratio (1.77:1, 1.85:1, 2.35:1 etc). They are quite different!

When it comes to encoding, there's quite alot of stuff to learn and get your head around. Maybe I'm giving you info you already know. If so, I apologise and hope it maybe useful to others instead.

Cheers

[hakko504]

hg, you are in Sweden: we use PAL. A PAL TV has 576 effective lines. Using anything but the full 720 wide is hurting the picture. The 640x480 is only an option for NTSC users.

[hassegubben]

Thank you guys!!! I really appreciate the expertice knowledge. I haven't done my homework. You answered all my questions. Yes, I am in PAL land and want the best image I can get on the TV. With recent codecs like the 5.x DivX, I have gained more bits and thus started encoding in 720*xxx(instead of 640*xxx). I was a bit worried though, that I wasted my bits on the resolution, since the bits/pixel have dropped to 12-13 in GKnot. I used to have a higher bits per pixel ratio when I used 640*xxx as encoding resolution. You have convinced me though, that keeping the original resolution is the better choice.

[hakko504]

Originally posted by hassegubben
I was a bit worried though, that I wasted my bits on the resolution, since the bits/pixel have dropped to 12-13 in GKnot. It has been said before, but it seems that it needs repeating so everybody gets it:
Bits/pixel should only be used as a reference before doing the first compression test. then when you know the result (%) of the compression test you should then trim the video so that the %age ends up in a reasonable range where 60-80% is recommended for a good quality video. It is very possible to acheive this and have bpp=0.01 or (more commonly) bpp=1.00 . There is no such thing as right or wrong in this case for bpp, only the compression test matter!.