Matte Filters in FCP
Matte Filters in FCP
It has been said that Compositing takes
place whenever there is more than one video track on the Timeline.
Mattes are used in FCP to make parts of a video image transparent
so that video on the tracks below can show through. In the Matte
Bin of the Effects Browser are nine different filters. A number
of these are actual Matte filters, the remaining items are filters
that can be applied to the matte filters for additional control.
Matte filters are used to shape that area of the video that we
want to become transparent and that part of the image that we
want to remain opaque.
Garbage Mattes - 4 and 8 Point
The Four and Eight Point Garbage Mattes
work in an identical manner. The Eight Point Garbage Matte has
four additional crop points that can be set.
Drag either the 4 or 8 point Garbage
Matte filter from the Effects Browser, Video filters, and drop
on to the clip on the Timeline. Park your playhead over the clip.
Double click on the filter to load into the Viewer, click on
the Filters tab.
In the Controls box. View Mode defaults
to 'Preview' which shows both the numbered crop points and video
with the matte active and transparent, showing the video on the
track below. My examples below have two video tracks, V1 and
V2, with two different landscapes. The Four Point Garbage Matte
is on V2. Final Mode shows the video only, no crop numbers. Wireframe,
the last option shows V2 only, crop points, and a white line
connecting the points.
View Mode - Preview
View Mode - Final
View Mode - Wireframe
The default positioning for the Crop points are the four corners
of the video frame. There are several ways to position the crop
points. In the Controls box are '+ buttons' for each of the Crop
points, 1,2 , 3 and 4. Click on the Crop button in Controls then
click in the Canvas window at the location that you want the
Crop point to be. Then move to the next numbered '+ button' and
set it. There are numeric fields for each of the Crop buttons
or you can select a '+' button in the Controls and then click
and hold on the small green Crop point in the Canvas. After a
few seconds you can slowly drag the Crop point to a new position,
be patient as this process is very slow.
There are several other controls used
with a Garbage Matte. 'Smooth' which rounds out the corners of
each of the Crop points. 'Choke' is used to enlarge or reduce
the size of the Matte created by the Crop points. The more 'Smooth'
that is applied the greater the changes that the 'Choke' setting
will produce. 'Feather Edges' is a must. This produces a semi
transparent border around the Matte that will soften or fade
the edges of the matte. There is an 'Invert' box which will flop
the transparent and opaque parts of the matte. 'Hide Labels'
will hide the Crop point numbers but not the green Crop points.
Point 1 set
Points 1, 2 and 3 set
Final with 'Feather Edges'
This Matte offers 4 different views,
with 'Source, Matte, Final' offering a 4-up view. I get the best
results when 'Final' is selected. There are three control sliders
which default to 50. There is an Invert box and 'Copy Results'
With Copy Results at its default setting
of 'to RGB' no compositing ability is present, this filter needs
only one clip. The RGB setting will produce a Black and White
image (shown below). Adjusting the slider controls will vary
the look. Adjusting the Soft slider higher than 50 will produce
more tone. Moving the slider below 50 will add contrast.
Normal video - no matte
Copy Results - to RGB
The Extract filter definitely becomes
more interesting when Copy Results is set to 'Alpha'. In this
mode the filter works like a luminance matte and composites with
a clip that is below it on the TL. Using the sliders you can
control which parts of the clip (V2) become transparent and which
parts stay opaque based on brightness.
Alpha - Threshold 57 - Tolerance
Alpha - Threshold 23 - Tolerance
The Image Mask filter uses only one video
clip on V1. In its Controls is an 'Image Well', Red arrow. The
video or image that is placed in the Image Well is composited
with the clip on V1. This is a simple tool with only two controls.
In the Channel drop down is Luminance, the default setting and
Alpha which does not seem to do much. The other control is 'Invert'
box which when checked reverses the composite.
This filter works by using the image
in the Image Well as a mask. Whatever parts of the Well image
are light in color become transparent allowing the video from
V1 to show through. Those parts of the image in the Well that
are dark become opaque blocking out the image from V1. Clicking
on the 'Invert' box will cause the light parts of the image in
the Well to become opaque and the dark parts to become transparent.
Video on V1
Image used in 'Image Well'
The Mask Shape Matte is a very useful
tool. It has four shape presets which you can then modify to
fit your needs. Diamond, Oval, Rectangle and Round Rectangle.
The size of the shape is controlled by the Horizontal and Vertical
settings which have sliders and numeric fields for control. I
have found that using the numeric fields to size the Matte is
the most useful. Clicking on 'Center' button in Controls and
then clicking in the Canvas window will set the position of the
Matte. There is an 'Invert' option for reversing the transparent
and opaque parts of the Matte.
In my example below I want to replace
the yellow sun in the fashion shot with the purple moon from
a landscape, Red arrows below. I have placed the fashion shot
on V1 and the landscape on V2 with the Mask Shape filter on the
landscape. This filter opens with the Rectangle shape as default
and a matte size of 50 x 50 pixels. You will notice that at this
point you can not see the purple moon in the landscape image.
I have selected the 'Oval' shape from
the Shape menu. Using the 'Center' button I have moved the matte
up so that it now shows the purple moon. I then further change
the shape and size of the matte so that it traps the moon.
In the Canvas window I have selected
'image+wireframe' from the Canvas drop down menu and dragged
the purple moon over the yellow sun in the fashion shot. With
the moon in position I got the 'Mask Feather' filter from the
Effects Browser and place it on V2, loaded it into the Viewer.
Setting 'Soft' to '1' feathers the matte and softens the edges
of the matte blending the two composited images.
The Mask Feather is not a matte. It is
to be used in conjunction with a matte and is used to soften
the edges of the matte. This is a very useful filter as it is
used to blend the edges of the image being composited.
I have started out with one image on
V1 to which I have applied the Shape Mask filter. After shaping
and sizing the matte I placed the Mask Feather filter on the
clip and set 'Soft' to 63.
Feather Mask at 63
Moving my image with Mask Shape and Mask
Feather up to V2, I placed a landscape beneath on V1. My one
last adjustment was to lower the Opacity of the clip on V2 to
blend it further into the landscape image.
Mask Shape - no Feather
Feather Mask - Opacity reduced
The Matte Choker filter is used in conjunction
with a matte. It's purpose is to change the size of a matte in
very small increments. Very small. By default this filter's control
'Edge Thin' is set to 0 in the middle of the slider. Moving the
slider to the left into negative numbers will make that matte
smaller, moving to right will make it larger. Again, I am talking
about very fine adjustments of maybe a pixel or less. The other
control, 'Edge Feather' will soften the edge but like 'Edge Thin'
the amount of change is minuscule.
The Soft Edges filter creates borders
around the video frame. The width of each border is independently
adjustable. When the border is set there is a choice of three
different corner styles; Round, Bevel and Cut. There are two
ways to soften the edges of the borders. Dither, which does not
seem to do much, and Gaussian, which does a great job of blending
the Edge area.
I really like this filter for two reasons.
If there is only one clip and Soft Edges is applied to it, the
Edges or borders default to black. You can achieve either very
soft edges or more dramatic ones if you like. But this is just
not an Edge filter, it's a compositing filter as well. In my
example, below right, the fashion clip with Soft Edges filter
on it has been moved up to V2 and a landscape image placed below
it on V1. Now the width of each border becomes an area of transparency
allowing V1 to show through. The lighter colored areas of V1
will show through the edges area. In my example I left the top
and bottom edges set to 5. I brought each side edge in by 60.
The edge of each boarder is almost completely transparent. This
creates a very soft look. I then used Gaussian to smooth it out
Soft Edges - V1 only
Soft Edges - V1 and V2 Video
In my examples I show the full video
image including 'overscan' with 'Soft Edges' applied to the outer
borders of my video image. As you know TV sets crop out the outer
edges of the video that we see in the Canvas window, the 'overscan'
portion. For this reason it is essential that you have 'Title
Safe' turned on in your Canvas window to judge where to place
your borders so that they will not be cropped out. It is equally
important to view your work on a NTSC monitor as well.
I have demonstrated this problem below.
The first image shows a full frame from my Canvas window. The
Soft Edges filters is applied to the outer edges of the Canvas
image (White arrow). The second image shows the same shot with
Title Safe turned on. As you can see, my Soft Edges are well
outside the Title Safe area (Red arrow) and would be lost when
viewed on a TV.
So you want that Widescreen look. This
filter will do it for you. It offers 7 different prebuilt Widescreen
formats. In addition to these seven sizes there is a 'Border'
setting which will allow you to further tweak the exact size
of the borders. You can use the 'Border' control to add a colored
border as well. You can click on the 'Color' box which will produce
a 'color wheel', you can use numeric values or you can use the
'eyedropper' to sample a color from your video to use as a border.
In the example lower right I used the eyedropper to sample some
green from my video. My border size is set to two. There is also
a 'Feather Edges' option which will slightly soften the border
edges. This setting has no controls and only one option for the
amount of the Feather.
1.78 Widescreen - Border
This filter would be some what limited
except for the fact that it has one last control called 'Offset'.
When you choose the format type from the Widescreen controls
you may not be happy with the placement of the video between
the top and bottom borders. With the 'Offset' control you can
actually shift your video up or down within the fixed borders.
Shown below, the first video on the left, is full frame video.
The middle example shows 'Offset' set to -100 which displays
the top part of the video and crops out the bottom part. The
example on the right shows a setting of +100 which displays the
bottom part of the video cropping out the top. Somewhere between
these two settings will be an optimum position for your video.
As mentioned before it is essential that
you have 'Title and Action Safe' overlays turned on in the Canvas
window when you set your Widescreen. You must always view your
final output on NTSC to check your work.
The Matte Bin in the Effects Browser
really is a mixed bag. The two Garbage Mattes and Mask Shape
Matte are workhorses of FCP compositing. Mask Feather and Matte
Choker are often used as well. You will often find that when
matting out images for compositing work, one matte will not do
the entire job. It is often necessary to apply several or different
mattes to the image to accomplish the job.
copyright © Ken Stone 2001
This article first appeared on www.kenstone.net and is reprinted here
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