[opendtv] Re: Math of oversampling - a simple comparison

Jeroen -

Thanks.  I've posted your two new images on my web site along with 
the others, though with no other doc except for this post.  But 
this brings the total collection to 5 images, listed below in 
chronological order:

1)  The left&right comparison of the Medium show that started all 
this.

        www.trbarry.com/Medium_1080p_compare_qtr_rez.jpg

2)  The left&right comparison of Leno (again the right filtered to 
  960x544)

        www.trbarry.com/Leno_1080p_compare_qtr_rez.jpg

3)  The original unfiltered Leno image

        www.trbarry.com/Leno_1080i.jpg

4)  Jeroen's Leno image creating by scaling to 544p and then back 
up to 1088p. Possibly softer but with fewer artifacts.

        www.trbarry.com/Leno_1080_544_1080p.jpg

5)  Jeroen's Leno image creating by scaling all the way down to 
480p and then back up to 1088p. Definitely softer but again with 
fewer artifacts.

BTW, I was thinking again about the discussion of artifacts being 
caused at the edges of the 8x8 blocks.  Of course I believe they 
will be created by MPEGx compression anyway.  But it on the way 
home today it occurred to me that for the cost of a few hundred 
vectorized multiplies and additions per pixel it would probably be 
possible to treat the entire image as one big block and avoid this 
problem anyway.

I need a faster computer.

- Tom


Jeroen Stessen wrote:

        www.trbarry.com/Leno_1080_480_1080p.jpg


> Dear Tom,=20
> 
> 
>>I've place a jpeg compressed version of the full untouched frame at:
>><www.trbarry.com/Leno=5F1080i.jpg> so you or anyone else can compare and =
> 
> 
>>play with it better.  Be interesting to see what you come up with.
> 
> 
> I send you back two files:=20
> <Leno=5F1080=5F544=5F1080p.jpg> and <Leno=5F1080=5F480=5F1080p.jpg>=20
> (attachments deleted for OpenDTV).=20
> 
> The first  file was generated: 1920x1088 -> 960x544p -> 1920x1088,=20
> the second file was generated: 1920x1088 -> 720x480p -> 1920x1088,=20
> 
> For the down-sampling I have used an 8-taps transposed polyphase=20
> filter (equivalent to a 16-taps impulse response low-pass filter)=20
> that has been optimized for low aliasing. It was applied in the=20
> linear-light domain, to simulate what an SD (p) camera would do.=20
> 
> For the up-sampling I have used a 6-taps polyphase filter (6-taps=20
> impulse response low-pass filter) that has been optimized more for=20
> high sharpness than for low aliasing. It was applied in the gamma=20
> domain, to simulate what a typical receiver would do.=20
> 
> There are some errors: the alignment of the output image is not=20
> exactly correct with the input image, and there are black bars=20
> around the image because I did not bother with filter run-in/out.=20
> Those can be fairly easily corrected in the design, but I have=20
> never bothered to. (That's why we have overscan, to not bother.)=20
> 
> I think that the sharpness loss is more significant than with=20
> your example, but the artefacts are milder and this is a true=20
> 2-step process with real filters with finite bandwidth (slope).=20
> So I think that this is a realistic example of what-if (480p).=20
> It can be significantly improved by receiver-side sharpness=20
> enhancement (=E0 la PixelPlus), but I did not apply that here.=20
> 
> I will post this same message, without attachments, on OpenDTV,=20
> and will you please put the images on your web-site and post a=20
> link to the messages ? Thanks.=20
> 
> Best regards,=20
> -- Jeroen=20
> 
> +-------------------------------+------------------------------------------+
> | From:     Jeroen H. Stessen   | E-mail:  Jeroen.Stessen@xxxxxxxxxxx |
> | Building: SFJ-5.22 Eindhoven  | Deptmt.: Philips Applied Technologies |
> | Phone:    ++31.40.2732739     | Visiting & mail address: Glaslaan 2 |
> | Mobile:   ++31.6.44680021     | NL 5616 LW Eindhoven, the Netherlands |
> | Pager:    ++31.6.65133818     | Website: http://www.apptech.philips.com/ =
> 
> |
> +-------------------------------+------------------------------------------+
> 
> 
>  
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