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Getting the "Movie Look" from Digital DV


I have been in discussion with others about a theory of mine for some time about NTSC 60i video that is destined to be film looked, either for direct video release, television broadcast or in theaters. Standard video runs at 60 interlaced frames per second at a standard shutter speed of 1/60th for each video field. One method used by many to convert video to give it that film feel is to combine fields and either go with a 30p conversion by taking field 1 and 2 and blending them together. If the 24fps look is desired, fields are combined then some more processing is done to create full frames to arrive at the 24fps speed. Motion picture cameras that photograph at 24fps usually are set at a shutter angle of 180 degrees, which translates into 1/48th second shutter speed per frame.

 

Here is where I have concentrated my research. Let's assume that we are going to emulate 30p with video acquired at 60i. We take as mentioned above field 1 and field 2 and combine them. Remove the interlace flicker with filtering. We now have full frame video that is emulating 30p DV. Each one of those fields has been recorded at 1/60th shutter speed with motion blur that is associated with that shutter setting. If you think about it, when these two fields are combined to make what we want to appear as one full frame, we are blending the motion blur and movement data of two separate points of time to make a full frame that appears as if it were captured all at once as a full frame from the beginning in-camera. Now this new full frame has more motion blur and image differences then it would have if we had shot at 30p full frame in-camera with a 1/60th setting from the beginning. By taking two fields with motion blurs of 1/60th captures and blending them together we are doubling the movement and blur information in that new full frame derived from blending fields 1 and 2. This would bring you to think that this would be emulating blur movement of a 1/30th approximate capture. If we actually had shot at 30fps progressive at 1/60th in-camera and compared it to the 60i blended field version, the in-camera 30p video would appear to have less blur then the 60i converted to simulation 30p.

 

The conversion process of blending fields appears to have too much motion blur. 60i video that's usually converted like this has always had a strange motion to it with a slightly slurry look or drag feel on movement. Maybe the reason that there is this appearance of excessive blur is that we are trying to force to much motion blur to happen at one point of time when combining fields from 60i video captured at 1/60th of a second into 30p. If we shot at 1/90th a second to reduce each fields motion blur slightly. When these fields are combined we would get the allusion of motion blur of 1/45th of a second. If we wanted the look of 1/50th motion blur, we could shoot the video at 1/100th and when theses fields are blended we would get the allusion of each full frame been acquired at 1/50th. There is a problem when increasing a DV cameras shutter speed with material destined to have it fields combined. When fields are combined that have to fast a shutter speed you will get what is called double image that shows to points of time that are overlapped that have very minimal blur. This does not look good on motion. Motion blur helps to hide the fact that these 60i video fields contain different points of time and the double image from blending fields together. So far 1/90th seems to be a good medium. More tests are being conducted at this time.

Source Michael Pappas