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  1. Member
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    First of all I am assuming DV sampling is 720 samples per line, that is the DV data actually has data for 720 points per line. Is this correct ?

    If so, then whats the point is collecting 720 samples when its going to get resized to 640 anyway whether it is being played on an old interlaced crt tv or a modern digital progressive monitor/tv ? Is there a way to somehow keep the full resolution all the way to the display device if that display is a digital progressive display capable of deinterlacing interlaced content itself ?
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  2. Because that was the standard for digitizing analog video for many years before DV and is sufficient to get all the resolution from a high quality analog source. It's not going to get resized to 640 pixels wide. It's going to get resized to whatever the final output size is. Ie, 1440x1080 or 1920x1080 on an HDTV. Even the analog SD output from a DVD player isn't 640 pixels wide. The 720 samples are sent do the DAC to produce the analog waveform.
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    Yes eventually it will get resized by the playback or display device, but when a DV AVI is converted to say MKV using a program like Handbrake, then doesn't it do that whole aspect ratio and par thing where it resizes to 480*1.33 = 720*.89 = 640 ? Thats what lead me to believe that the converted file itself is resized in the first place. If that is not true I'd be happy to know but then where and how does 640 come into the picture ? In Handbrake when the Anamorphic option is disabled ('none') it automatically flips the resolution to 640 from 720 (shown below).

    If you mention "rectnagular pixels", please do explain with an example which display device could have rectangular pixels ? How do they physically exist ? That is one thing I have never been able to understand.Click image for larger version

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  4. Video Restorer lordsmurf's Avatar
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    Originally Posted by Movie-Maker View Post
    Yes eventually it will get resized by the playback or display device,
    No, it does not.
    It gets resampled for display. It's not resized.
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  5. Originally Posted by Movie-Maker View Post
    If you mention "rectnagular pixels", please do explain with an example which display device could have rectangular pixels ? How do they physically exist ? That is one thing I have never been able to understand.
    Rectangular pixel is a figure of speech, they do not exist. What player does, when encountering anamorphic video, is reading aspect ratio.
    Assuming playing NTSC DV avi using monitor, aspect ratio is 8:9(that is standard for NTSC DV 4/3). So Player knows that he has to stretch horizontal resolution using that storage aspect ratio (or whatever it is correctly named). It uses whatever algorithm to do it. For example, if you set player to full screen (1920x1080) it renders 1440x1080 out of those 720x480.

    Why it knows to stretch it to 1440? First it calculates viewing aspect ratio: 720x8/9=640, then 640/480=4/3. It knows 4/3 is rendering aspect ratio. It knows also your screen aspect ratio of your monitor. So then it figures out what side would touch the edge of your screen, if top and bottom, it upscales vertical resolution to 1080, then sides get black bars to fill the screen - it upscales horizontal resolution 720 into 1440: 1080/480=2.25x was vertical resolution upscaled, so horizontal resolution must be upscaled with same amount: 720x8/9x2.25=1440

    ... that I just made up, calculation cold have gone very different way, but with the same principle, anamorphic video gets just upscaled (or downscaled) .Regular video, non-anamorphic is rendered exactly the same way, except aspect ratio is 1.0 (instead of those 8/9) in those calculations

    Resizing is happening almost all the time when you view standard resolution video on HD screen. It makes not much difference if it is anamorphic or not, it gets resized (or resampled as lordsmurf says) anyway from something to something.
    Last edited by _Al_; 15th May 2015 at 00:29.
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  6. Member
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    Ok thanks. Couple of followup questions if you dont mind -

    What is the definition of anamorphic ? Any video that does not have an aspect ratio of 1:1 or PAR of 1 ?

    When I convert from AVI to another format (say mkv or mp4 or mpeg2) then does the converter do any resizing (720->640) at all ? or does it leave it as is ?
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  7. Pixels have no shape, they are points. When you speak of pixel aspect ratio what you are really referring to is the spacing between those points. So a pixel aspect ratio (more properly called a sampling aspect ratio) of 8:9 means the separation of the points horizontally is 8/9 the vertical spacing.

    When you convert videos you may or may not retain the original frame size. It depends on the software you use, your personal preference, and playback hardware limitations.
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  8. Banned
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    It is simple:

    720 > 640.

    So anyone who first cuts resolution to 640 for "holy standards" or what have you and then upscales it to HD 720 or HD 1080 does not know what he is doing.

    Last edited by newpball; 15th May 2015 at 16:43.
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  9. Member Cornucopia's Avatar
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  10. By the way, DV conforms to the rec.601 standard for pixel aspect ratio. That means the 4:3 picture is contained in a 704x480 portion of the 720x480 frame. So the full frame is a little wider than 4:3.
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