Good video quality, but unsharp text

[Marthax]

Hello everybody!

I've been reading a lot here at doom9.org and you've all helped me out a lot but unfortunately, I haven't managed to solve my current problem. The problem is that when I encode video clip (which I resized from 1280x960 -> 640x480) using x264, the text in the clip gets unsharp. Now, I don't mean the subs, but a text at the top right corner of the clip that belongs to it. Everything looks just fine, but this unsharpness makes it really difficult to read.
I've probably missed something, but what?

Thanks in advance!

Marthax

[check]

It's probably because you are halving the resolution of it. If there is text on the screen of a video, reducing the resolution really reduces the quality of it.

[setarip_old]

(I'm nitpicking here) - Actually, you're reducing the resolution to one quarter of the original resolution...

[Marthax]

I always thought that if you resize it from a larger to a smaller res, you get better quality because more pixels are gathered together on the same spot. Why doesn't this apply?
Then how about resizing it to a larger res? Will the image quality change if I change it from 640x480 to 1280x960?

If there is text on the screen of a video, reducing the resolution really reduces the quality of it. Is there any explanation behind this? Why do the quality of the text reduce when you resize from higher to lower res?

(I'm nitpicking here) - Actually, you're reducing the resolution to one quarter of the original resolution... Why one quarter?

[mod]

Why do the quality of the text reduce when you resize from higher to lower res?
When you reduce the resolution, you "decimate" the number of pixels of the text (and of the whole img of course).
When you enlarge it again during playback, you have LESS pixels and they get "interpolated" to reach the "original" area.
The text doesn't look good because during all this process you loose contrast.

EDIT:Why one quarter?
Given a rect with

size = width*heigth

if you apply

width = width/2
heigth = heigth/2

you get a rect with size = size/4.

[Marthax]

Oh, I see. Thanks for pointing that out :) Appreciate it.

Well, then I suppose that resizing from a smaller to a larger res. is ever more foolish, or am I wrong?

[mod]

I suppose that resizing from a smaller to a larger res. is ever more foolish, or am I wrong?
The advantage is that in this 2nd case you can use some filtering to make your text more "clear", and the decoder doesn't reproduce "wrong" informations interpolating the video..

[Marthax]

What about the video itself? Will it's quality get worse?

EDIT: Oh, one more thing.

I thought about this When you enlarge it again during playback, you have LESS pixels and they get "interpolated" to reach the "original" area. and I can't seem to figure it out. If you resize a video to a smaller resolution, why do the player resize it back during playback?

[mod]

What about the video itself? Will it's quality get worse?
It depends by a lot of factors.. :)

If you resize a video to a smaller resolution, why do the player resize it back during playback?
I thought about it too before posting :)
I assumed that you didn't watch the material in a reduced screen area, because you said that the text looks "bad": this implies a comparison between two images of the same (or similar) dimension..
So.. I'm sorry if I'm not clear here, not my language.. the idea is that, considered an area of the same dimensions on your screen, if the decoder has less pixels then it has to interpolate, if has too much then it has to decimate..

[Marthax]

And by decimate I assume you mean "remove", right?

[mod]

Yes, as you wrote in your post (#4):
I always thought that if you resize it from a larger to a smaller res, you get better quality because more pixels are gathered together on the same spot.
Note that you get more bits per pixel (same bitrate and less pixels..), but this doesn't mean that the quality is higher.. it simply means that you can keep more infos, but with a reduced resolution..

[Marthax]

I see. Thanks for clearing that out for me :)

[mod]

np :)