Resize to full res square pixels before down scaling ?

[WorBry]

For Pal DV to MPEG-4/AVC conversion, I have been in the habit of resizing (after deinterlacing) directly to 720x544 (Edit:720x528 :rolleyes: old habits die hard) (720x400 for widescreen) with LanczosResize, and then denoising.

Recently I received advice that for 16:3 anamorphic DV (720x576) it is preferable to first size to 'full' square pixel resolution (1048x576) before down-scaling, to avoid introducing additional artifacts, unless "you have very good software that can scale the image without distortion".

Would appreciate the comments of our resident experts on this.

If this is considered sound practice:

a) Should the same be applied to 4:3 DV i.e. first size to 788x576 and then 'downscale' to 720x544 (Edit:720x528 :rolleyes: again )

b) Would Bicubic be a better choice for initial sizing?

c) Are there any particular benefits, in terms of image quality, in denoising before down-scaling (I know it will be slower).

I'm processing in YV12

Thanks alot.

[scharfis_brain]

Just only use one single resizing step.
Multiple resizing can result in blurry image detail.

[WorBry]

Thought so. Thanks Scharfis.

[halsboss]

Note sure if this thread helps or hinders ... here it is anyway http://forum.doom9.org/showthread.php?p=1019318#post1019318

[WorBry]

halsboss, thanks for the link, which, in its context, is enlightening.

However, my query specifically concerned square pixel rendering for MPEG-4/AVC, not DVD. I'm sure no-one would argue a case for intermediate sizing of DV to full square pixel res before encoding to MPEG-2, as the (native) source and final resolutions are the same (I dont crop anything) and, AFAIK, Avisynth filters (denoisers, colour correction etc), at least, dont require square pixel input to function correctly; if there are exceptions to this, I would be interested to know.

BTW - if anyone is a little confused (as I was) about PAR and holds that full square pixel AR should be 768x576 for 4:3 and 1024x576 for anamorphic 16:9 (as I previously did), here's a nice little tutorial that illustrates it well:

http://vistavision.de/tutorials/palvideo/tutorial_pal_4x3.html