why all the fuss about choosing the resolution?

[Psymaster]

I've been doing dvd rips using divx 502 and gknot and I had no problems. I really think it's the best app out there. I always follow the guides. They put big emphasis on choosing the "right" resolution by doing comp. checks etc.

But, I've been thinking lately, isn't all this useless? I mean, we take a dvd at the typical 720x576. What's the point in encoding lower than 640x??? if we're gonna view it at at least 640x480?

I am thinking of having a lower limit of resolutions in my rips from now on, @ 640x???. Is it a right decision? What do you think? Am I geting sth wrong here?

[jggimi]

I would bet that the majority of GKnot users are like me, doing 2-pass encodings, trying to get the best possible quality at a specific file size.

Both quality and size predicitability are impacted by resolution. That's why there's such a focus on it.

For short material where size is not a factor, I do 1-pass encodings at Quant 2.

For those shorts, I suppose I could eliminate the resizing command from the .avs entirely, as long as I crop with the correct modulo limitations...though I have to say I've I've never tried it.

[Psymaster]

Both quality and size predicitability are impacted by resolution. That's why there's such a focus on it.

If the comp check directs me to use a res like 576x??? what will change if I use 640x??? anyway if i'm gonna view it on my pc at 640x480? Wouldn't it be better?

[jggimi]

...what will change if I use 640x??? Bitrate. With direct impact on the quality of the image.


And, from empirical evidence with compressibility testing, you will likely miss your desired file size.

[jggimi]

I'm wrong.

(Manono corrected me via e-mail, so I'm still living up to my tagline.)

Bitrate doesn't change.

The larger the resolution, the fewer bits available to each block of pixels. Quality is something of a balancing act.

[Psymaster]

And, from empirical evidence with compressibility testing, you will likely miss your desired file size.

No, if I put 700 MB in gknot I'll get 700 MB no matter which res I choose. So Manono is right.

The larger the resolution, the fewer bits available to each block of pixels.

That is know by definition.

Quality is something of a balancing act.

I think I didn't get that.

The question remains. If I will always watch my divx on my monitor @640x480, shouldn't I always encode @640x??? ? What's the point in choosing a res below that if I will anyway change it when I view it? If someone knows please reply.

[N_F]

This is the way I see it (don't ask me to back it up with technical answers):

If you encode at low resolutions and then watch it in fullscreen the picture will be blocky.
If you encode at higher resolutions and then watch it in fullscreen the picture will be more blurry.

A while ago I did some experiments with different resolutions for the same scene. I tried to as low as 320 x xxx and as high as 800 x xxx. The 320 x xxx were blocky as hell in fullscreen while the 800 x xxx was very blurry, both of them locked very bad. I also compared 640 x xxx and 576 x xxx. I preferred 576 x xxx. Perhaps 640 x xxx would have been the better one if there'd been more bits available, i e a higher bitrate.


Helpful?

[Psymaster]

Helpful?

Yes, of course.

But were all your test encodes at the same filesize?

[N_F]

I don't remember if I used 2-pass or quality based. But it doesn't matter, if you use quality based the filesize will be different. If you use 2-pass encoding the filesize will be the same, as long as the codec isn't maxed out, in which case you may end up with a smaller filesize.

[jggimi]

Psymaster wrote:No, if I put 700 MB in gknot I'll get 700 MB no matter which res I choose... Not quite. Compressibility will have an impact on final filesize. Loading factors above 80% are unlikely to reach your desired result, as N_F mentions.

In addition, loading factors under 60% appear to produce results that appear, subjectively "too blocky" according to most who've reported results here.

These two reasons are why compression tests are recommended for setting resolutions for a desired file size.

[TheWEF]

Originally posted by Psymaster
If the comp check directs me to use a res like 576x??? what will change if I use 640x??? anyway if i'm gonna view it on my pc at 640x480? Wouldn't it be better?


higher resolution -> more compression artefacts, blocks.
lower resolution -> less detail, more blur.

and there is a resolution with the best balance...

wef.