Q10: 4:3 interlaced to 16:9 anamorphic
Often people ask themselves how to convert a 4:3 interlaced shot into a 16:9 anamorphic video (interlaced, too). To achieve this, you crop away everything outside the 16:9 window of your 4:3 frame; typically you keep the center part of the frame. Then you upsize the cropped video to get back a full sized DV frame. But how much to crop? How to resize correctly to keep the aspect ratio, thus avoiding "egg heads"? How to deal with the interlacing?
The answers differ depending on the TV standard. Although the formulas are the same, the crop and resize values differ because of the different frame sizes. Here are the answers.
NTSC:
Code:
frame........720x480
field........720x240
4:3 AR.......1.500
4:3 DAR......1.333
PAR..........0.889
16:9 AR......2.000
16:9 DAR.....1.778
16:9 frame...720x360
crop total...120 pixels
NTSC example script:
Code:
AviSource("C:\DV\test.avi")
# alternatively: DirectShowSource("C:\DV\test.avi")
Crop(0,60,0,-60)
SeparateFields()
BicubicResize(720,240)
ConverttoYUY2()
ReInterpolate411()
odd=SelectOdd.Convolution3D(1, 6, 10, 6, 8, 2.8, 0)
evn=SelectEven.Convolution3D(1, 6, 10, 6, 8, 2.8, 0)
Interleave(evn,odd)
Weave()
# BFF to TFF: DoubleWeave.SelectOdd()
PAL:
Code:
frame........720x576
field........720x288
4:3 AR.......1.250
4:3 DAR......1.333
PAR..........1.067
16:9 AR......1.667
16:9 DAR.....1.778
16:9 frame...720x432
crop total...144 pixels
PAL example script:
Code:
AviSource("C:\DV\test.avi")
# alternatively: DirectShowSource("C:\DV\test.avi")
Crop(0,72,0,-72)
SeparateFields()
BicubicResize(720,288)
ConverttoYUY2()
odd=SelectOdd.Convolution3D(1, 6, 10, 6, 8, 2.8, 0)
evn=SelectEven.Convolution3D(1, 6, 10, 6, 8, 2.8, 0)
Interleave(evn,odd)
Weave()
# BFF to TFF: DoubleWeave.SelectOdd()
Feed the script into your favourite MPEG-2 encoder, and remember to switch the 16:9 flag on. This will tell your player that it has to deal with anamorphic content, i.e. it has to resize to 16:9 display.
Now that you know how to turn your 4:3 footage into 16:9 anamorphic, let me add a note which you might want to consider:
During the abovementioned process you crop your video, then you upsize it to full frame (field) size. You don't gain information in this process, you merely "blow up" the video. That means you'll need more bitrate to encode it later.
An alternative is to encode 4:3 letterboxed and use your TV set's 16:9 zoom. This way you save bitrate while preserving the same picture quality. All you have to do is to crop and add back black borders of the same size, which can be done in a single Letterbox command in AviSynth.