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  • Resizing DVD's with Correct Aspect Ratio's

    Some people are real sticklers for getting perfect aspect ratio. But it's almost impossible to get a perfect aspect ratio when we are limited to resizing by 16 pixel jumps every time! It makes cropping awkward and it also limits us to weird sizes. I have to admit that I haven't always followed perfect aspect ratios but this time I think I've got it right.



    The picture below is taken from a 4:3 DVD. If your DVD is an aspect ratio of 4:3 then there's nothing to it! All PAL (European) DVD's use 720 x 576 pixels and all NTSC (north American) DVD's use 720 x 480 pixels. This means a perfect aspect ratio should be 1.33:1.

    And, since we must resize in blocks of 16 x 16 pixels, this makes the following the closest sizes. Remember that the closer to 1.33:1 it is the more exact the aspect ratio to a 4:3 TV screen:

    PAL/NTSC 720 x 576 / 720 x 480
    Size Ratio
    720 x 544 1.32:1
    640 x 480 1.33:1
    592 x 448 1.32:1
    544 x 416 1.30:1
    512 x 384 1.33:1
    448 x 336 1.33:1
    400 x 304 1.32:1
    384 x 288 1.33:1
    336 x 256 1:31:1
    320 x 240 1.33:1

    For DivX rips I'd recommend something like 448 x 336 or even 384 x 288 for PAL and for NTSC you can go as low as 336 x 256 since you're used to 20% less TV resolution than the rest of the word, he he! I've tended to change my mind a lot on what I consider to be the best sizes to use, but I shy away from very large sizes because they cause too many artifacts. Also, full DVD resolutions will very often cause jerky playback. This will happen as often as the Divx hits a keyframe. For my 500Mhz CPU the DivX codec seems to give an optimum smooth playback with under 1000 blocks of 16 x 16 pixels before problems. Therefore a full 720 x 576 resolution DivX with 1620 blocks is no good for me. If you intend on making DivX's that will play on just about anyone's machine, then I suggest you consider this fact.



    Here is where life gets tricky. Firstly, many DVD's will say something like: 2.35:1 Anamorphic (Approx.) the "approx" part doesn't inspire confidence in me =). If you have read the section on Anamorphic DVD's you will know that they rip at 720 x 576 (or 720 x 480) and will give a squashed picture like this one:

    For those of you who use Flask Mpeg the rest of this information may not be needed. Because, if you check the maintain aspect ratio option, it will stretch the movie to the correct shape for you. But you still may have problems with those god accursed NTSC movies! Hence, the following information will be useful for getting correct aspect ratios in Flask when you keep the aspect ratio option turned off.


    STRETCHING 16:9 / 24:10

    2.35:1 WideScreen is probably the most used anamorphic size in Europe. But because we are limited to 16 x 16 blocks (because of the limitations of the mpeg format), the only size that is exactly 2.35:1 is 640 x 272 pixels. Actually, its an aspect ratio of 2.35294117647059:1 if you really want to impress your friends =).

    These are some of the closest:

    672 x 288 (2.33:1)
    640 x 272 (2.35:1)
    528 x 224 (2.36:1)

    But that's a bunch of bunk though! If you just resize an anamorphic DVD to 2.35:1 you'll see the incredible pancake show! This is basically because even anamorphic DVD's are still recorded with black bars at the top and bottom of the image. DVD's only support 4:3 and 16:9 aspect ratios. In other words they can be either 1.33:1 or 1.85:1. If another size is needed such as 2.35:1 then they will squish the picture on the DVD itself so that when it is resized to either 1.33:1 or 1.85:1 it will look the correct shape. This means the following sizes are the most common to use. The closer to a ratio of 1.85:1 the better.

    PAL/NTSC 720 x 576 / 720 x 480
    Size Ratio
    720 x 384 1.87:1
    640 x 336 1.87:1
    576 x 304 1.89:1
    512 x 272 1.88:1
    480 x 256 1.87:1
    448 x 240 1.86:1



    I cannot list every possible situation. So instead, there is a great utility called CM's Digital Video Tool. It can do many things, but its most useful feature is its ability to calculate aspect ratios for us. Get the application Here.

    Lets assume you want to resize your movie to be somewhere between 550-600 pixels across in size. It is an anamorphic 2.35:1 movie so we must use the aspect ratio of 1.85:1 to put it right. Right, so we open Digital Video Tools, select the 'Datarate Calculator' tab and click on the bit I've encircled in red.

    It will change to the following display:

    From the drop down menu you can choose some standard settings such as 4:3 or 16:9 etc. But you can ignore this drop down menu completely if you like! The most important thing is to make sure the 'Align by 16' box is always ticked and the 'Lock aspect' box is not ticked until I tell you :). Then follow these three simple steps:

    Step 1.

    Move the slider bars left and right until you get the correct aspect ratio you need. It will appear in the box to the far left of the picture (in the picture above it is: 1.80:1). Forget the size settings on the right (in the picture above are 720 x 400). The important thing is to get the aspect ratio correct. If you cannot get it exactly then get it as close as possible. So, for example, if you cannot get 1.85:1 you could use 1.86:1 and it would still look almost the same.

    Step 2.
    Once you know the aspect ratio is correct tick the 'Lock aspect' box to keep it always the same.
    Step 3.
    Finally, move either slider bar until the movie is the resolution you want it. For example, I moved it down to 576 x 320 and this gave me a pretty close aspect ratio to1.85:1 because I wanted the video 576 wide.

    That's it! Now you should be able to figure out any aspect ratio you want. But here are some helpful guidelines to save some time:

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