You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
279 lines
14 KiB
279 lines
14 KiB
4 years ago
|
<!-- saved from url=(0022)http://internet.e-mail -->
|
||
|
|
<html>
|
||
|
|
<head>
|
||
|
|
<title>Smart Deinterlacing Filter</title>
|
||
|
|
</head>
|
||
|
|
<body><font face=verdana>
|
||
|
|
<center><h2>Smart Deinterlacing Filter<br><small>(Version 2.6)</small></h2></center>
|
||
|
|
<small>[Place this HTML file in the VirtualDub plugins directory to
|
||
|
|
make it available via the Help button on the filter configuration
|
||
|
|
dialog box. The computer must have an HTML browser, such as Internet
|
||
|
|
Explorer or Netscape,
|
||
|
|
available in its search path.]</small>
|
||
|
|
<p>
|
||
|
|
This filter provides a smart, motion-based deinterlacing capability. In static
|
||
|
|
picture areas, interlacing artifacts do not appear, so data from both fields is
|
||
|
|
used to provide full detail. In moving areas, deinterlacing is performed. Also,
|
||
|
|
some clips derived from telecined material can appear to be interlaced when in fact
|
||
|
|
they only require field shift and/or swaps to recover progressive (noninterlaced)
|
||
|
|
frames. The filter provides advanced processing options to deal with these clips.
|
||
|
|
<p>
|
||
|
|
The following options are available:
|
||
|
|
<p>
|
||
|
|
<h3>Motion Processing</h3>
|
||
|
|
|
||
|
|
<b><i>Frame-only differencing</i></b>: When this option is checked (default), only inter-frame
|
||
|
|
comparisons are made to detect motion. If a pixel differs from the corresponding
|
||
|
|
pixel in the previous frame, the pixel is considered to be moving.
|
||
|
|
<p>
|
||
|
|
<b><i>Field-only differencing</i></b>: When this option is checked, only inter-field
|
||
|
|
comparisons are made to detect motion. If a pixel differs from the corresponding
|
||
|
|
pixels in the previous and following fields (the lines above and below the current
|
||
|
|
line), the pixel is considered to be moving.
|
||
|
|
<p>
|
||
|
|
<b><i>Frame-and-field differencing</i></b>: When this option is checked, both inter-frame and
|
||
|
|
inter-field comparisons are made to detect motion. If a pixel differs from the
|
||
|
|
corresponding pixel in both the previous field and the previous frame, the pixel
|
||
|
|
is considered to be moving.
|
||
|
|
<p>
|
||
|
|
The correct choice for differencing depends on the input video; each mode has problems
|
||
|
|
with some kinds of clips. Field-only differencing alone may tend to overestimate motion.
|
||
|
|
Frame-only and frame-and-field differencing may tend to underestimate it.
|
||
|
|
Also to be considered is execution time; frame-only will be the
|
||
|
|
fastest, followed by field-only, followed by frame-and-field.
|
||
|
|
<p>
|
||
|
|
In my experience, good results with a wide range of clips are obtained with frame-only
|
||
|
|
differencing at a threshold of 15, and so these are
|
||
|
|
the filter defaults. Motion map denoising is helpful with field-only differencing
|
||
|
|
as it reduces the amount of picture detail that is erroneously detected as motion.
|
||
|
|
<p>
|
||
|
|
<b><i>Compare color channels instead of luma</i></b>: When comparing pixels, if this box is unchecked
|
||
|
|
(default), the lumanance values are compared. When this box is checked, the individual
|
||
|
|
color channels (red, green, and blue) are compared. Luma comparison is good for general
|
||
|
|
video and especially where static alpha-blended logos appear (because video noise can
|
||
|
|
cause subtle color changes that would be detected by color channel compares). Color
|
||
|
|
channel comparisons are good for cartoons and other clips with large solid color areas.
|
||
|
|
<p>
|
||
|
|
<b><i>Show motion areas only</i></b>: When selected, only the moving areas of the image
|
||
|
|
are displayed; static areas are black. This option can be used to assess the
|
||
|
|
suitability of the choice of option settings and threshold.
|
||
|
|
<p>
|
||
|
|
<b><i>Blend instead of interpolate in motion areas</i></b>: If this checkbox is not selected (default),
|
||
|
|
then, in motion areas, the filter will discard one field's data and recreate it
|
||
|
|
by interpolating new lines from the retained field's lines. In static areas, both
|
||
|
|
field's data is used. If this checkbox is checked, then, in motion areas, instead
|
||
|
|
of interpolating, the filter blends each line with the lines above and below. This
|
||
|
|
has the effect of blending the fields, which tends to blur out the interlacing
|
||
|
|
artifacts. The choice of interpolation versus blending depends on the nature of
|
||
|
|
the input video and your own esthetic preferences. The interpolate mode avoids
|
||
|
|
the halos you can get with the blend mode, but it introduces some small amount
|
||
|
|
of stairstepping, and may tend to emphasize any video noise that is present. Try
|
||
|
|
both ways and see which you prefer for a given video clip.
|
||
|
|
<p>
|
||
|
|
<b><i>Use cubic for interpolation</i></b>: When doing line interpolation (not blending), if
|
||
|
|
this option is not selected, a linear interpolation using two lines is used. If this option is
|
||
|
|
selected, a cubic interpolation using 4 lines is used. Cubic interpolation is better but
|
||
|
|
slower.
|
||
|
|
<p>
|
||
|
|
<b><i>Motion map denoising</i></b>: A dilemma for users of the filter is that to get the best deinterlacing,
|
||
|
|
we like a low threshold, such as 10-15. A low threshold ensures that residual interlacing
|
||
|
|
artifacts don't sneak through. But if we set the threshold too low, video noise gets
|
||
|
|
detected as motion. This causes two undesirable results. First, the motion noise causes
|
||
|
|
a random sprinkling of deinterlaced areas in what should be static areas. This often
|
||
|
|
manifests as a kind of sparkling, which is objectionable. Second, any extra false
|
||
|
|
motion that is detected reduces the picture area that is passed through from both fields,
|
||
|
|
reducing the perceived resolution of the overall picture. So, what we want is a low threshold
|
||
|
|
but without the effects of video noise. When this checkbox is checked, extra
|
||
|
|
filtering is added in the motion detection pipeline (not in the main video pipeline, so the
|
||
|
|
ouput video is not compromised) that does a good job of suppressing false motion noise.
|
||
|
|
The downside is that the filter runs slower. Use the "Show motion areas only" option to
|
||
|
|
tweak the threshold fairly low without introducing false motion noise. This
|
||
|
|
option is especially helpful with field-only differencing.
|
||
|
|
<p>
|
||
|
|
<b><i>Motion Threshold</i></b>: This value determines the difference between a pixel and its corresponding
|
||
|
|
value in the previous field or frame that must be exceeded for the pixel to be considered
|
||
|
|
moving. A threshold that is too high will allow interlacing artifacts to slip through. A
|
||
|
|
threshold that is too low will cause too much of the image to be treated as moving,
|
||
|
|
reducing the perceived resolution. A too-low threshold will also tend to emphasize noise.
|
||
|
|
Without motion map denoising (see above), a threshold of 15-25 is good.
|
||
|
|
With denoising, 10-20 is good. You can view the effect of threshold on motion detection
|
||
|
|
by selecting the "Show motion areas only" checkbox.
|
||
|
|
<p>
|
||
|
|
<b><i>Scene Change Threshold</i></b>: Sometimes when a scene change occurs between the fields of
|
||
|
|
a frame, the result is not satisfactory. This option permits you to set a threshold of change such
|
||
|
|
that if the threshold is exceeded, the entire frame will be treated as moving, i.e., the
|
||
|
|
entire frame will be interpolated or blended. The value to be specified is the percentage of
|
||
|
|
moving area detected; for example, with the default value of 30, if 30 percent or more of
|
||
|
|
the frame is detected to be moving, the entire frame will be treated as moving. Note that
|
||
|
|
the percentage calculation is made prior to motion-map denoising (if enabled).
|
||
|
|
|
||
|
|
<h3>Advanced Processing</h3>
|
||
|
|
|
||
|
|
Advanced Processing is most often used for "deinterlacing" captured PAL video originally
|
||
|
|
made from films. If you have movies that seem to be interlaced, it is worth trying
|
||
|
|
the advanced processing first, because it may allow you to recover the original progressive
|
||
|
|
frames without quality loss. Because the processing is sufficient to recover the original
|
||
|
|
progressive frames, full motion processing is usually disabled when Advanced Processing is
|
||
|
|
enabled. But some capture cards do weird things when they capture, and if you are
|
||
|
|
unlucky enough to have such a card, you may need to enable one or more of the Advanced
|
||
|
|
Processing options and perform Motion Processing. Hopefully, the analysis below will help
|
||
|
|
you to determine if you are so affected.
|
||
|
|
<p>
|
||
|
|
Before proceeding into the analysis, please note that, due to
|
||
|
|
the way that this filter buffers frames internally, it may appear to not work correctly when
|
||
|
|
scrubbing the time line or when single stepping backward. But single stepping forward will
|
||
|
|
always work and, of course, saved processed video will always be correct. It is always advisable
|
||
|
|
to hit the rewind button before starting processing.
|
||
|
|
|
||
|
|
<h4>Technical Explanation</h4>
|
||
|
|
|
||
|
|
I give the technical explanation first, then I explain what the options do. The former is
|
||
|
|
necessary to understand the latter.
|
||
|
|
<p>
|
||
|
|
First, it is necessary to understand how capture cards might vary. Let us assume that the
|
||
|
|
source material is simply a stream of bottom and top fields, as follows:
|
||
|
|
<p>
|
||
|
|
b1t1b2t2b3t3b4t4...
|
||
|
|
<p>
|
||
|
|
The symbol 'b' indicates a bottom field and 't' indicates a top field.
|
||
|
|
The number indicates the frame number of the original progressive frame. Thus, fields
|
||
|
|
b1 and t1 are both from frame 1 and contain information from the same temporal moment.
|
||
|
|
<p>
|
||
|
|
The capture card will capture this stream in memory, varying in two ways. First, it might
|
||
|
|
start capturing on a bottom field or a top field. Second, it might place either the bottom field
|
||
|
|
or the top field first in memory. This leads to 4 ways in which the stream may be captured,
|
||
|
|
as follows:
|
||
|
|
<p>
|
||
|
|
1) b1t1-b2t2-b3t3-b4t4...<br>
|
||
|
|
2) t1b1-t2b2-t3b3-t4b4...<br>
|
||
|
|
3) t1b2-t2b3-t3b4-t4b5...<br>
|
||
|
|
4) b2t1-b3t2-b4t3-b5t4...
|
||
|
|
<p>
|
||
|
|
where the '-' character indicates a frame boundary. A given capture card will be characterised
|
||
|
|
by which of these capture patterns it uses. Note that if capture pattern 1 is used, no filtering
|
||
|
|
is needed to re-create the original progressive frames.
|
||
|
|
<p>
|
||
|
|
It might seem that all we need to do now is to define the operations that the filter must
|
||
|
|
perform to change each of the above capture patterns to the desired deinterlaced end result
|
||
|
|
b1t1-b2t2-b3t3-b4t4. That would only tell half the story. The problem is that there is an
|
||
|
|
alternative form for the input stream! Consider these two ways in which the original material
|
||
|
|
may be telecined:
|
||
|
|
<p>
|
||
|
|
1) b1t1b2t2b3t3b4t4... (as before)<br>
|
||
|
|
2) b1t2b2t3b3t4b4t5... ('perverse' telecining)
|
||
|
|
<p>
|
||
|
|
Note that both will appear fine when displayed on an interlaced display, but a capture of
|
||
|
|
telecine type 2 with capture pattern 1 will no longer give deinterlaced output
|
||
|
|
on a progressive display without filtering! This means that we must now consider 8 patterns,
|
||
|
|
i.e., 4 capture patterns times 2 telecining types. For each type, we will have a specific operation
|
||
|
|
that will need to be done to re-create the original progressive frames. We see below that by
|
||
|
|
combining 3 building blocks we can cover all the possibilities. The building blocks are applied
|
||
|
|
in order and each one is optional:
|
||
|
|
<p>
|
||
|
|
swap fields on input --> shift field phase by one --> swap fields on output
|
||
|
|
<p>
|
||
|
|
A phase shift by one means that a stream b1t1-b2t2-b3t3... becomes xxb1-t1b2-t2b3-t3b4...
|
||
|
|
<p>
|
||
|
|
Following are all 8 possibilities together with the processing required for each:
|
||
|
|
<p>
|
||
|
|
<b><i>Case 1</i></b>: Telecine 1, capture 1 gives after capture:
|
||
|
|
<p>
|
||
|
|
b1t1-b2t2-b3t3...
|
||
|
|
<p>
|
||
|
|
Required action: none.
|
||
|
|
<p>
|
||
|
|
<b><i>Case 2</i></b>: Telecine 1, capture 2, gives after capture:
|
||
|
|
<p>
|
||
|
|
t1b1-t2b2-t3b3...
|
||
|
|
<p>
|
||
|
|
Required action: swap on input.
|
||
|
|
<p>
|
||
|
|
<b><i>Case 3</i></b>: Telecine 1, capture 3, gives after capture:
|
||
|
|
<p>
|
||
|
|
t1b2-t2b3-t3b4...
|
||
|
|
<p>
|
||
|
|
Required action: phase shift.
|
||
|
|
<p>
|
||
|
|
<b><i>Case 4</i></b>: Telecine 1, capture 4, gives after capture:
|
||
|
|
<p>
|
||
|
|
b2t1-b3t2-b4t3...
|
||
|
|
<p>
|
||
|
|
Required action: swap on input, followed by phase shift.
|
||
|
|
<p>
|
||
|
|
<b><i>Case 5</i></b>: Telecine 2, capture 1, gives after capture:
|
||
|
|
<p>
|
||
|
|
b1t2-b2t3-b3t4...
|
||
|
|
<p>
|
||
|
|
Required action: phase shift, followed by swap on output.
|
||
|
|
<p>
|
||
|
|
<b><i>Case 6</i></b>: Telecine 2, capture 2, gives after capture:
|
||
|
|
<p>
|
||
|
|
t2b1-t3b2-t4b3...
|
||
|
|
<p>
|
||
|
|
Required action: swap on input, followed by phase shift, followed by swap on output.
|
||
|
|
<p>
|
||
|
|
<b><i>Case 7</i></b>: Telecine 2, capture 3, gives after capture:
|
||
|
|
<p>
|
||
|
|
t2b2-t3b3-t4b4...
|
||
|
|
<p>
|
||
|
|
Required action: swap on input.
|
||
|
|
<p>
|
||
|
|
<b><i>Case 8</i></b>: Telecine 2, capture 4, gives after capture:
|
||
|
|
<p>
|
||
|
|
b2t2-b3t3-b4t4...
|
||
|
|
<p>
|
||
|
|
Required action: none.
|
||
|
|
<p>
|
||
|
|
Unfortunately, it is not a trivial matter to determine which correction to apply.
|
||
|
|
If one is sure that the material is telecined from progressive material, one can try
|
||
|
|
all possibilities. When the correct one is found, one then knows for the future what the
|
||
|
|
capture pattern must be for the capture card used. Thereafter, only two corrections
|
||
|
|
need be tried to allow for the two possible telecine patterns. I wish things were simpler,
|
||
|
|
but, alas, it is not so.
|
||
|
|
<p>
|
||
|
|
Note also that the telecining method can change in mid-clip. This filter does not adapt to
|
||
|
|
such changes. A different filter, Telecide, is available that can adapt to such changes
|
||
|
|
and output a continuous stream of progressive frames.
|
||
|
|
<p>
|
||
|
|
<h4>Advanced Processing Settings</h4>
|
||
|
|
|
||
|
|
The advanced processing settings allow the possible 8 corrections to be applied. Simply check
|
||
|
|
a given building block if you want it enabled.
|
||
|
|
<p>
|
||
|
|
<b><i>Field swap before phase shift</i></b>: Swaps the fields of the frames before an optional phase shift.
|
||
|
|
<p>
|
||
|
|
<b><i>Phase shift</i></b>: Shifts the field phase by one, i.e., b1t1-b2t2-b3t3... becomes
|
||
|
|
xxb1-t1b2-t2b3-t3b4...
|
||
|
|
<p>
|
||
|
|
<b><i>Field swap after phase shift</i></b>: Swaps the fields of the frames after an optional phase shift.
|
||
|
|
<p>
|
||
|
|
<b><i>Disable motion processing</i></b>: When checked the filter will perform only the Advanced Processing and
|
||
|
|
will not follow it with normal motion processing. This is useful for getting only a shift and/or
|
||
|
|
swap when that is sufficient for processing telecined material. When this is unchecked the
|
||
|
|
Advanced Processing will be performed first and then full motion processing will be performed.
|
||
|
|
|
||
|
|
<h3>Note on 3:2 Pulldown, Etc.</h3>
|
||
|
|
|
||
|
|
Some video streams are created from progressive video by a process called pulldown.
|
||
|
|
This results in a mixture of progressive and interlaced frames, from which it is theoretically
|
||
|
|
possible to recreate the original progressive frames without doing motion-adaptive deinterlacing.
|
||
|
|
It is technically very challenging to write a filter that will recreate the original
|
||
|
|
frames for all types of pulldown and in the presence of video edits, etc. I have created
|
||
|
|
a filter that performs this function reasonably well (Telecide) and you may find that
|
||
|
|
it meets all your needs. As an alternative, motion-adaptive deinterlacing will function quite
|
||
|
|
acceptably for the majority of these video streams. Finally, some people use Telecide followed
|
||
|
|
by Smart Deinterlacer in field-only mode to catch any interlaced frames that slip through
|
||
|
|
Telecide.
|
||
|
|
<p>
|
||
|
|
For additional information, version updates, and other filters, please go to the following web site:
|
||
|
|
<p>
|
||
|
|
Filters for VirtualDub<br>
|
||
|
|
<a href=http://sauron.mordor.net/dgraft/index.html>
|
||
|
|
http://sauron.mordor.net/dgraft/index.html</a>
|
||
|
|
<p>
|
||
|
|
Donald Graft<br>
|
||
|
|
August 6, 2001<br>
|
||
|
|
(C) Copyright 1999-2001, All Rights Reserved
|
||
|
|
</body>
|
||
|
|
</html>
|