Welcome to Doom9's Forum, THE in-place to be for everyone interested in DVD conversion. Before you start posting please read the forum rules. By posting to this forum you agree to abide by the rules. |
26th December 2005, 10:25 | #1 | Link |
Registered User
Join Date: Nov 2005
Posts: 6
|
Is it true that quadpel improve visual quality?
i am developing wavelet based video codecs.i have implemented half pel,but i want to improve visual quality of picture ,can i go for quadpel to improve quality .Which interpolation is best for quadpel please help me?
|
26th December 2005, 12:41 | #2 | Link | |
Registered User
Join Date: Nov 2001
Posts: 9,770
|
Quote:
avc/h.264 always uses qpel
__________________
Between the weak and the strong one it is the freedom which oppresses and the law that liberates (Jean Jacques Rousseau) I know, that I know nothing (Socrates) MPEG-4 ASP FAQ | AVC/H.264 FAQ | AAC FAQ | MP4 FAQ | MP4Menu stores DVD Menus in MP4 (guide) Ogg Theora | Ogg Vorbis use WM9 today and get Micro$oft controlling the A/V market tomorrow for free |
|
27th December 2005, 01:40 | #3 | Link |
Banned
Join Date: May 2005
Location: Serbia
Posts: 560
|
Anz idea about 1/8 frame motion search, exact double compared with qpel prediction?
I meant, qpel is two times simplier then opel (1/8 frame search). I suppose, somewhere in 2008 H.264 will use this, and become H.264+ standard. |
27th December 2005, 02:04 | #4 | Link |
Registered User
Join Date: Apr 2004
Posts: 1,315
|
qpel is not 1/4 of frame. Qpel - quarter pixel (1/4 pixel). 1/8 pixel in future? Hm .. I doubt.
Half of pixel 0.5 . Qpel (for exaple 0.25-0.75) already requires (usefull it or not it would spend approx 30-45 kbit/s for usual DVDrip resolution) some extra bits but increase sharpness usefully. Thatīs why for very low bitrate it sometimes better not to set Qpel. 1/8 pel will requeires even more bits. I don't know if it will be usefull trade on blockness/sharpness. Indeed Dev's commentaries are welcome. Last edited by IgorC; 27th December 2005 at 02:10. |
27th December 2005, 09:11 | #5 | Link |
Registered User
Join Date: Jan 2002
Location: France
Posts: 2,856
|
h264 was planned initially with 1/8th pel motion compensation. It has been dropped ( except for the chroma ), because it lacked efficiency. A better motion precision doesn't allow a better sharpness ( that's the interpolation filter that sets the sharpness, hpel could be sharp if it was made to ), but it allows a better prediction, which means les bits will be taken by the dct coefficient. However, more bits will be taken by motion vectors. from halfpel to qpel, it's still worth it. But from qpel to 1/8th pel, it seems it doesn't.
__________________
|
27th December 2005, 11:53 | #6 | Link |
Registered User
Join Date: Nov 2001
Posts: 9,770
|
at least they could have given us the choice!
__________________
Between the weak and the strong one it is the freedom which oppresses and the law that liberates (Jean Jacques Rousseau) I know, that I know nothing (Socrates) MPEG-4 ASP FAQ | AVC/H.264 FAQ | AAC FAQ | MP4 FAQ | MP4Menu stores DVD Menus in MP4 (guide) Ogg Theora | Ogg Vorbis use WM9 today and get Micro$oft controlling the A/V market tomorrow for free |
27th December 2005, 20:03 | #7 | Link | |
Senior n00b
Join Date: Jan 2004
Location: Italy
Posts: 446
|
Quote:
IIRC for chroma in 4:2:0 it's not really "1/8th pixel", but "1/8th sample". That is, along every axis you compute 8 values from the original sample. Given that in 4:2:0 each chroma sample is taken every two pixels, then 2 / 8 = 0.25 and so interpolated chroma planes are effectively "1/4th pixel" in resolution like luma. </nitpicking> (hope I'm remembering things correctly ) |
|
6th January 2006, 01:26 | #10 | Link |
Registered User
Join Date: Dec 2005
Location: Qetchua mountains in Peru, and Klingon battlecruiser D'Mar
Posts: 393
|
Well, H.264 format is still in early development, so let wait and see! Who knows, what future will bring to us?
__________________
Live long and prosperLive long and prosperLive long and prosper |
6th January 2006, 16:58 | #11 | Link |
Registered User
Join Date: Mar 2002
Posts: 1,075
|
AFAIK 1/8 pel was dropped for complexity, not performance.
Nilgosavi, you should read the papers here (start with the one from Thomas Wedi). PS. I think making better and better linear interpolation filters is completely missing the point. There is a fundamental mismatch between how images are captured and linear filtering. PPS. I wonder how much the impression of sharpness for qpel is just a side effect of the ringing of the filter (it works a bit like unsharp). Last edited by MfA; 6th January 2006 at 23:40. |
6th January 2006, 21:19 | #12 | Link | |
Registered User
Join Date: Apr 2003
Location: Czech Republic
Posts: 752
|
Quote:
|
|
11th January 2006, 13:37 | #13 | Link | |
Clouded
Join Date: Jul 2003
Location: Cambridge, UK
Posts: 1,148
|
Quote:
__________________
a.k.a. Clouded. Come and help by making sure your favourite AVISynth filters and scripts are listed. |
|
11th January 2006, 17:25 | #14 | Link |
Registered User
Join Date: Mar 2002
Posts: 1,075
|
Not exactly, usually point spread functions are approximated as anisotropic gaussians (in linear colourspace of course). Though it's not really all that important to me, any good model would be too complex to be of use for making a filter
What I find relevant is that pixels are effectively area sampled. Not point samples on a bandwith limited signal, that's not how cameras work and that is not how our own visual system works. The effect that has on stuff like resampling is often lost on people, even those who should know better. The amount of times I have seen it said that the Sinc doesn't work out to be the ideal resampling filter because the extent is not infinite in practice is sad. Last edited by MfA; 11th January 2006 at 17:27. |
11th January 2006, 18:13 | #15 | Link | |
Clouded
Join Date: Jul 2003
Location: Cambridge, UK
Posts: 1,148
|
Thanks for the reply!
Quote:
Something I've been meaning to do for a long time is to take a perfect zoom (no internal motion -- not hard to find in animation, which is my main area of interest), and use a Fourier transform to extract the camera sampling kernel empirically... but of course this assumes that the various layers of (probably tape) transmission between source and DVD haven't messed things up too much. Edit: and also assuming that the sampling kernel is the same for all zoom factors... which is a big assumption. (That's the kind of thing I searched for information on.)
__________________
a.k.a. Clouded. Come and help by making sure your favourite AVISynth filters and scripts are listed. Last edited by mg262; 11th January 2006 at 19:27. |
|
12th January 2006, 05:37 | #16 | Link |
Registered User
Join Date: Mar 2002
Posts: 1,075
|
Looking at it as a point sampled signal doesn't help, since from a conventional point of view you just end up with a whole lotta aliasing. Talking about it in terms associated with filtering on critically sampled signals just reinforces bad habits in people ...
As long as there is any motion for which you have a good description you could simply assume a higher resolution ground truth and extract an overdetermined set of linear equations to find the PSF. I just don't see the point though ... it's not really relevant to the kind of ad hoc algorithms Im interested in. Just googling for ccd and point-spread-function seems to provide decent results. For a CCD it is roughly a box shape, with tapered edges and lots of spikes. Last edited by MfA; 12th January 2006 at 05:45. |
12th January 2006, 14:14 | #17 | Link | ||||
Clouded
Join Date: Jul 2003
Location: Cambridge, UK
Posts: 1,148
|
Quote:
Quote:
Quote:
Edit: Quote:
__________________
a.k.a. Clouded. Come and help by making sure your favourite AVISynth filters and scripts are listed. Last edited by mg262; 12th January 2006 at 14:32. |
||||
12th January 2006, 19:16 | #18 | Link |
Registered User
Join Date: Mar 2002
Posts: 1,075
|
Without knowing the extent of the errors you are introducing thinking that using a physical PSF for deconvolution will get you closer to the ground truth is hopefull thinking at best. My guess is that simply directly using your favourite linear interpolation and unsharp with visually tweaked parameters will perform equally and look better.
|
Thread Tools | Search this Thread |
Display Modes | |
|
|