3:2 Pulldown Node

The 3:2 Pulldown node enables you to convert imagery from the frame rate of film (24 fps) to the frame rate of video (30 fps). By video, we are actually referring to the 525/60 scan rate associated with NTSC video. (The PAL video standard, on the other hand, is associated with the 625/50 scan rate. Typically, the transfer from 24 fps to 50 fps is accomplished by a simple doubling.)

To convert video to the frame rate of film, use the complementary 3:2 Pushup Node .

The 3:2 Pulldown node accepts one input and functions by creating five fields from every two input frames by replicating one field from every other frame. The following figure illustrates the functionality of the node, using a typical 3:2 pattern.

Selecting a Phase Shift

There are two basic pulldown patterns used to pad the frames to 60 fields per second: 3:2 and 2:3. However, there are a total of five different permutations, or phase shifts, necessary to match the footage being transferred to other video footage, depending on how it has been created and edited.

Depending on the system used for a pulldown, these variations may be referred to using different terminology. The following chart can be used as a guide if you, or those you need to communicate with about the process, are familiar with different terms:

The choice of phase shift only becomes important if the film sequence to be transferred will be spliced into other video sequences or if the footage will eventually be transferred back to film speed:

  • For footage that will be combined with an existing video sequence, the important thing is to sync the phase shift pattern based on how the other video clip has been edited.
  • For footage that will eventually be transferred back to 24 fps, the key is to use the matching phase shift pattern for both transfers.

Tip:
Click the Info ("i") button on the 3:2 Pulldown node to find out which input frames were used as the source of the odd and even field lines that compose the current frame of the output.

Selecting a Field Order

Field Order refers to whether the odd field lines of each frame are assigned to field 1 and the even field lines to field 2, or vice versa. (Note that this parameter does not refer to selecting field dominance, that is, to selecting F1 or F2 as the field you always edit on.)

Executing a 3:2 Pulldown Sequence

By the nature of the conversion operation, additional frames are created. Therefore, to render a sequence that has passed through a 3:2 pulldown node, you must specify Start and End values in the Exec node panel that correspond to the actual number of frames resulting from the pulldown operation--not the frame range of the original input.

For example, a six-second, 144-frame film sequence that is processed through the 3:2 Pulldown node becomes 180 frames long. To execute the entire sequence, you would key a value of 1 into the Start parameter field of the Exec node and a value of 180 into the End field.

Tip:
The Frame Range parameter on the Info tab of each node displays the length of the sequence as output from the node. (To actually calculate the number of frames in the output of a pulldown, you would multiply the number of input frames by 5, and divide the result by 4.)

To process only a portion of the total input sequence, it is important to add a Sequence node between the input node and the 3:2 Pulldown node in order to specify the frames to be used.

For example, to convert only the action occurring during the last four seconds of a six-second film sequence, key a Start value of 49 and an End value of 144 into the Sequence node entry panel. The Sequence node will then deliver the image data in frame 49 of the source imagery to the 3:2 Pulldown node, but the frame number is remapped to 1.

The Sequence node and the Exec node are described in chapter 13, "Tool Nodes ."

Pulldown Parameter Tab

Phase Shift

This parameter enables you to select the type of conversion the 3:2 Pulldown node should use. Select A, B, C, D, or E from the Phase Shift popup menu to specify a repeating field pattern. The most commonly used patterns are A and B:

Select "A" from the Phase Shift menu to use a " 2:3" pattern...

  • where the first video frame is made up of two fields based on the first film frame, the second video frame is made up of two fields based on the second film frame, and the third video frame is made up of one field based on the second film frame and one field based on the third film frame, and so on in a repeating 2:3 pattern.

Select "B" from the Phase Shift menu to use a " 3:2" pattern...

  • where the first video frame is made up of two fields based on the first film frame, and the second video frame is made up of one field based on the first film frame and one field based on the second film frame, and so on in a repeating 3:2 pattern.

Field Order

This parameter specifies whether the odd fields (lines 1, 3, 5, etc.) should be used to create field 1, with the interlacing even fields (lines 2, 4, 6 etc.) comprising field 2, or vice versa. It refers to spatial precedence and one choice should be used consistently throughout a facility.

Even, Odd

The even fields are used to create the first field and the odd fields are used to create the second field.

Odd, Even

The odd fields are used to create the first field and the even fields are used to create the second field.




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