Field Selector

PieroF_Field_Selector_v1.3R.fxscript.zip: (click the link to Download)

What does it do ?

Field Selector is a freeware filter for Final Cut Express and Final Cut Pro whose purpose is to display only one field of each video frame. You can select which field to display; the other field, that is not selected, may be made transparent to show clips in the tracks below.

It allows to analyze each field separately, for example to check the comb effect or to control the field sequence in a movie, or also to modify each field separately in a frame; this is possible if you apply the simple procedure described in the Example at the end of this page.

Warning: Field Selector does not swap nor slip fields, and it does not de-interlace video: it simply shows or hides each single field (technically is the simplest filter I can imagine: a couple of if statements and 4 lines of fxscript code... you can check it yourself!).

For example, from the original clip:

...you can select the first or the second field (they are different in moving scenes):

...and you can choose to make the other field transparent to show an underlying clip:

To get this effect you must stack the 2 clips in 2 different tracks in the timeline, apply the Field Selector filter to the higher clip; with the option “From clips: THIS and BELOW” the first field of the higher clip and the second field of the lower clip will be used.

The clip in the lower track used in the example above is:

Note: Both fields are visible in the Canvas or in the Viewer as in the pictures above only if their Zoom is set exactly to 100% (not Fit to Window nor any other value); otherwise only the second field is displayed as if it were de-interlaced, even if the actual media is not de-interlaced. In addition it might be necessary to set RT = Safe RT (not Unlimited RT) if you want an immediate view of the fields, without rendering first.

Compatibility, Disclaimer

This Field Selector filter has been tested in Final Cut Express HD v3.5 and Final Cut Pro v5.1, but it will likely work also in other versions of FCE and FCP as long as they provide support for the fxscript language (see also the Disclaimer).

Version History

v1.3 - added “Both (PIP)”, and moved to pf-toolbox.

v1.1 - changed the user interface, and added the possibility to show only the “other” field.

v0.3 - completely restructured release: removed the Image Well and made the transparent option available for the alternate field.

v0.2 - first release.

Filter Usage

After its Installation drag the filter Field Selector v1.3 from the Video Filter > pf-toolbox folder of Effects into the Viewer on the clip you want to apply it to, set the zoom for the Canvas window to 100% to see the effect of the filter, and then choose:

•Select Field (in this clip) (default: First): defines which field from the clip will be used (see also Note on field order below):
‣First: the first output field contains the first field in the clip, or a black field depending on the From clips option; the second output field instead is either black or transparent (see below).
‣Second: the second output field contains the second field in the clip or a black field depending on the From clips option; the first output field instead is either black or transparent (see below).
‣Both (PIP): both the first and the second field are displayed side by side as 2 Pictures in Pictures (PIPs): the left one shows a scaled down version of the first field and the right one shows a scaled down version of the second field.
In this case the From clips control below is ignored.
•From clips (default: THIS only): depending on this control:
‣THIS only: only one field is displayed, taken from the clip where Field Selector is applied (this clip): only the first or only the second field is displayed, depending on the Select Field control;
‣THIS and BELOW: two fields are displayed: one field is taken from the clip where Field Selector is applied (this clip), the other field is taken from the clip below this clip: whether the first field is taken from this clip or the clip below depends on the Select Field control (see table below);
‣BELOW only: only one field is displayed, taken from the clip below this clip: only the second or only the first field is displayed, depending on the Select Field control.
In the last two cases, in order to show the clip below the field is made transparent.
•PIP Scale (%) (default: 50%): it defines the scaling factor for the case Select Field: Both (PIP). It is ignored otherwise.
As a result the possible combinations of the first two controls are the following ones:

Important: After applying the filter and setting its controls render the clip to see its final effect: without rendering and without setting the zoom to 100% you cannot see the effect in the canvas or the viewer.

As an alternative you might set RT = Safe RT (not Unlimited RT) if you want an immediate view of the fields, without rendering first. The zoom = 100% is always necessary to see the 2 fields at the same time.

Example n.1:

You can use Field Selector to apply 2 different filters (or filter settings) to each field in a clip.

To do that you must:

1.stack 2 copies of the clip in 2 different tracks in the timeline (e.g. by alt-select-shift-dragging the clip from a track to another)
2.apply 2 different filters or filter settings to the 2 copies of the clip
3.apply Field Selector to the top copy of the clip, making sure From clips: = THIS and BELOW.
As a result FCP or FCE will apply one filter to the first field and the other filter (or settings) to the second field.
In the example below the RGB Balance filter is applied to both the top clip and the bottom clip, but in the top clip Greens > Highlights is set to its maximum value, while in the bottom clip Reds > Highlights is set to its maximum value. In addition Field Selector is added to the top clip and depending on its settings these are the different results:

In the 3rd picture you can see the result of applying different settings of the RGB Balance Filter to the different fields of the same frame: Green > Highlights to the 1st field and Red > Highlights to the 2nd field.
Since the person in the picture is moving left, at his right you can easily see a greenish comb (due to the 1st green field) and, on its left, a reddish comb (due to the 2nd red field). This isn’t necessarily showing a good use of the RGB Balance Filter (this is not the purpose here), but it should clarify how the Field Selector works.

Example n.2:

If only a single frame has to be corrected or modified (e.g. for fixing dropouts or removing scratch) you have first to cut that frame out, for example using the blade tool, and then apply the above procedure to that 1-frame clip.

Example n.3:

The following is an example of display of Select Field: Both (PIP). The figure gives only a rough idea of the result, since it cannot be displayed full size; in any case differences between the 2 fields might be difficult to see, unless some object moves rapidly in the movie.
You can see the 1st and the 2nd field on the left and the right of the frame respectively.
If needed you can also scale both PIPs with values different from the default (50%).

Note on field order:

In this filter “first” and “second” field refer to the time when the field appears, not to its position within the frame. So in PAL the first field comes 1/50th of second before the second field, and in NTSC it comes 1/60th (roughly) of second before the second field.

Instead the position of a field in a frame depends on its timing and its movie Field Dominance, so:

•if Field Dominance = Lower (Even) (true for both DV-NTSC and DV-PAL):
‣the “first” field is the lower field, on frame rows 2, 4, 6, etc. and
‣the “second” field is the upper field, on frame rows 1, 3, 5, etc.
•if Field Dominance = Upper (Odd) it’s the other way around:
‣the “first” field is the upper field, on frame rows 1, 3, 5, etc. and
‣the “second” field is the lower field, on frame rows 2, 4, 6, etc