Checking The Trackers

Pre-Solve Tracker Checking　解析前のトラッカーチェック

 訳者注）グラフのポイントはVelocity Spikes（速度スパイク）を見つけることにあるようです。

トラッカーが途中で間違ったものを追ってしまった場合、一瞬にして別の場所へ移動します。トラッカーの移動速度が一瞬上がるわけです。これを見つけだすことで不正なトラッカーを見つけだすことができます。

（以下本文）

手動トラッキングをしているとき、十分なトラッカーがショットを通して配置できていることを確認するために、ショットを解析し始める前に定期的にトラッカーをチェックしなければなりません。
ショットを解析し始める前、自動トラッキングの後にも、トラッカーをチェックすることができます。
（単純なショットの場合、自動トラッカーでトラッキングから解析までを直接行うことができます。）

 このセクションは、解析する前にトラッカーを検査する方法を記載します。
SynthEyesGraph Editorを紹介します。
解析した後に、clean-up toolを含む、他のテクニックとツールを利用できます。

Tip：以下のツール・ティプスの内、自動トラッカーは灰色、 手動トラッカーは金色の背景が表示されます。

 

Checking the Tracker Trails　トラッカー・テイルをチェックする

以下の手順は、問題あるトラッカーと状態（例えば、あまりに役に立つトラッカーが少ないフレームなど）を直ぐにチェックする方法です。

1. カメラ・ビューへ移動してください
2.メインまたは右クリック・メニューで、View/Show Imageをオフにしてください。
3.ショットのタイム・バー上で、クリック&ドラッグで左右にマウスを動かし(スクラブし)、以下を探してください
　・多くのトラッカーがないイメージの領域
　・全イメージが多くのトラッカーを持っていないショットの部分
　・他と違った方向に動いているトラッカー
4. メインまたは右クリック・メニューでView/Show tracker trailsをオンにしてください。
5. ショットのタイム・バー上でスクラブし、以下を探してください
　・トラックの始まりか最後のおかしいフック（特に画像の端で現れます）
　・テイルが不連続にジグザグしているもの。
イメージなしの方がモーション・パスを分析しやすいはずです。おそらく、イメージ自体によって惑わされないからです。

このプロセスは、問題の多いショット(低いパースペクティブによるショット、三脚で突然撮られたショット、若干のドリーまたは揺れている三脚ショット、中央のどこかに少しズームがあるショット)の性質を決定するのに有効です。

 

Checking Tracker Lifetimes

 Graph Editorのトラックビューでショットを通してフレーム毎にどのくらい多くのトラッカーが有効か概要をみることができます。

graph editorはツールバーのボタンを使用してフローティングウインドウにすることができます。また、それは、それ自体によるビューポートとして、または、他のビューポート構成の一部とにすることができます。

グラフ・エディタを開けたあと、以前に再生していたならば、それがトラック・ビューであることを確認してください。
ショットが手動トラッキングであるならば、アルファベットソートからタイムソートにしてください。

ウインドウの大きさを変更したならば、横スケーリングもリセットしてください。

次にパネルの右下ののボタンをクリックします。選択すると、トラッカーカウントバックグラウンドが見えている状態で、キーが消え、グラフが圧縮されます。グラフエディタはこのようにみえるはずです。

 

各バーは一つのトラッカーに対応しています。 Tracker4は選択されていて、強調されています。 色分けされたバックグラウンドは、トラッカーの数が、左で問題が多く、中央はOKで、右で安全を示します。 あなたは好きに、セーフレベルを構成できます。 このレベル(デフォルト12)を超えると、バックグラウンドは白くなるでしょう(グレーを暗いUI設定にしてください)。 しかし、セーフレベルを下回ると、バックグラウンドは"Ok"の、緑色の明るい色合いになるでしょう。 トラッカーの数はOKですが、希望するセーフレベルに達するほど高いわけではありません。 この圧縮された画面はトラッカーがショットの間中どう分配されているかにおける素晴らしいクイック・ルックを与えます。 色分けは三脚台モードショットと保持領域があるショットにより異なります。 ウェイトが0のトラッカーは数えません。

Hint: When the graph editor is in graph mode, you can look at a direct graph of the number of valid trackers on each frame by turning on the #Normal channel of the Active Trackers node.

If there are unavoidably too few trackers on some frames, you can use the Skip Frames track on theFeature Control Panel to proceed.

The graph editor is divided into three main areas: a hierarchy area at top left, a canvas area at top right, and a tool area at the bottom. You can change the width of the hierarchy area by sliding the gutter on its right. You can partially or completely close the tool area with the toolbox at left. A minimal view is particularly handy when the graph editor is embedded in a viewport layout.

In the hierarchy area. you can select trackers by clicking their line. You can control-click to toggle selections, or shift-drag to select a range. The scrollbar at left scrolls the hierarchy area.

You can also select trackers in the canvas area in squish mode, using the same mouse operations as in the hierarchy area.

The icons next to the tracker name provide quick control over the tracker visibility, color, lock status, and enable.

Warning: you can not change the enable, or much else, of a tracker while it is locked!

The small green swatch shows the display color of a tracker or mesh. Double-clicking brings up the color selection dialog so you can change the display color. You can shift-click a color, and add all trackers of that color to the current selection, control-click the swatch of an unselected tracker to select only trackers of that color, or control-click the swatch on a selected tracker to unselect the trackers of that color.

Jumping ahead, the graph editor hierarchy also shows any coordinate-system lock settings for each tracker:

x, y, and z for the respective axis constraints;

l (lower-case L) when there is a linked tracker on the same object;

i for a linked tracker on a different object (an indirect link);

d for a distance constraint;

0 for a zero-weighted tracker;

p for a pegged tracker;

F for a tracker you specified to be far;

f for a tracker not requested to be far, but solved as far for cause.

Introduction to Tracker Graphs

The graph editor helps you find bad trackers and identify the bad portions of their track. The graph editor has a very extensive feature set that we will begin to overview; for full details see thegraph editor reference. We won’t get to the process of how to find the worst ones until the end of the section, when you understand the viewport.

To begin, open the graph editor and select the graphs mode. Selecting a tracker, or exposing its contents, causes its graphs to appear.

In this example, a tracker suddenly started jumping along fence posts, from pole to pole on three consecutive frames. The red curve is the horizontal U velocity, the green is the vertical V velocity, and the purple curve is the tracker figure-of-merit (for supervised trackers). You can see the channels listed under Tracker15 at left. The green circles show which channels are shown; zoom, pan, and color controls are adjacent. Double-clicking will turn on or off all the related channels.

There are a variety of different curves available, not only for the trackers but for other node types within SynthEyes.

The graph editor is amult-curveeditor—any number of completely different kinds of curves can be displayed simultaneously. There is no single set of coordinate values in the vertical direction because the zoom and pan can be different for each kind of channel. To determine the numeric value at any particular point on a curve, put the mouse over it and the tooltip will pop up with the set of values.

The graph editor displays curves for each node that is exposed (its channels are displayed; Enable, U. Vel, V. Vel, etc above).

The graph editor also displays curves for all selected nodes (trackers, cameras, or moving objects) as long as theDraw Curves for Selected Nodesbutton is turned on. This gives you quite a bit of quick control over what is drawn, and enables you to compare a single tracker or camera's curves to any other tracker as you run through them all, for example.

You zoom a channel by dragging the small zoom icon. The zoom setting is shared between all channels with the same type. For example, the U and V velocity channels are the same type, as are the X, Y, and Z position channels of the camera. But the U velocity and U position are different types. If you click on the small Zoom icon, the other zoom icons of the same type will flash.

The zoom setting is also shared between nodes of the same type: zooming or panning on one tracker affects the other trackers too. All related channels will zoom also, so that the channels remain comparable to one another. This saves time and helps prevents some incorrect thought patterns.

The pan setting is also shared between nodes, but not between channels: the U velocity and V velocity can be separated out. When you pan, you’ll see a horizontal line that is the “zero level” of the channel. It will snap slightly to horizontal grid lines, making it easier to make several different curves line up to the same location. You can later check on the zero level by tapping the zoom or pan icons.

There are two kinds of auto-zooms, activated by double-clicking the zoom or pan icons. The zoom double-click auto-zooms, but makes all channel of the same type have the same zero level. The pan double-click auto-zooms, but pans the channels individually. As a result, the zoom double-click keeps the data more organized and easier to follow, but the pan double-click allows for a higher zoom factor, because the zero levels can be different.

For example, consider zooming an X position that runs 0 to 1, and a Y position that runs 10 to 12.

If we pan double-click, the X curve will run full-screen from 0 to 2, and Y will run full-screen from 10 to 12. Note that X is not 0 to 1, because it must have the same zoom factor as Y. X will only occupy the bottom half of the screen.

If we zoom double-click, X will run from 0 to 12 full screen, and Y will run from 0 to 12 full screen. The range and zero locations of both curves will be the same, and we’ll be better-able to see the relationship between the two curves. But if we want to see details, the pan-double-click is a better choice.

There is no option to have X run 0 to 1 and Y run 10 to 12, by design.

Both zoom and pan settings can be reset by right-clicking on the respective icons.

Interpreting Figure of Merit

 

In this example, two trackers have been supervised-tracked with a Key Every setting of 20 frames (but starting at different frames). The tracker Figure of Merit (FOM) curve measures the amount of difference between the tracker's reference pattern and what is found in the image. You see it drop down to zero each time there is a key, because then the reference and image are the same.

One tracker has a small FOM value that stays mostly constant. The other tracker has a much larger FOM, and in part of the shot it is much larger. In a supervised shot, the reason for that should be investigated.

You can use this curve to help decide how often to place a key automatically. The 20 frame value shown above is plenty for those features. If you see the following, you should reduce the spacing between keys.

 

You’ll also be able to see the effect of theKey Smoothsetting: the key smoothing will flatten out a steadily increasing curve into a gently rounded hump, which will reduce spikes in the final camera path.

Velocity Spikes

Here's an example of a velocity curve from the graph editor:

At frame 217, the tracker jumped about 3 pixels right, to a very similar feature. At frame 218, it jumped back, resulting in the distinctive sawtooth pattern the U velocity curve exhibits. If left as-is, this spike will result in a small glitch in the camera path on frame 217. 

You can repair it using theTracker control panel in the main user interface by going to frame 217. Jiggle back and forth a few frames with the S and D keys to see what's happening, then unlock the tracker and drop down a new key or two. Step around to re-track the surrounding frames with the new keys (or rewind and play through the entire sequence, which is most reliable).

DeGlitch Mode

You can also repair the glitch by switching to the Deglitch mode of the graph editor, then clicking on the first (positive) peak of the U velocity at frame 217. SynthEyes will compute a new tracker location that is the average of the prior and following locations. For most shots, this will eliminate the spike.

If you see a velocity spike in one direction only, it will be more difficult to correct: it means that the tracker has jumped to a nearby feature, and not come back. You will have to put it back in its correct location and then play (track) through the rest of the shot.

The deglitch tool can also chop off the first or last frame of a tracker, which can be affected when an object moves in front, or a feature is moving offscreen. Even if the last two or three frames are bad, you can click a few times and quickly chop them off.

Finding Spikes Before Solving

Learn to recognize these velocity spikes directly. There are double spikes when a tracker jumps off course and returns, single spikes when it jumps off course to a similar feature and stays there, large sawtooth areas where it is chattering between near-identical features (or needs a new position key for reference), or big takeoff ramps where it gets lost and heads off into featureless territory.

To help find these issues, the graph editor features the Isolate mode. Left-click it to turn it on, then right-click it to select all the trackers (it does not have to be on for right-clicking to work).

With all the trackers selected, you will usually see a common pattern for most of the trackers, plus a few spots where things stick out. If you click the mouse over the spikes that stick out, that tracker will be selected for further investigation. You can push the left button and keep it down and move around investigating different curves, before releasing it to select a particular one. It can be quicker to delete extra automatic trackers, rather than repairing them.

After repairing each tracker, you can right-click the isolate button again, and look for more. With two monitors, you can put the graph editor on one, and the camera view on another. With only one monitor, it may be easiest to operate the graph editor from the Camera & Graphs viewport configuration. Once you are done, do arefine-mode solving cycle.

Hint: You can stay in Deglitch mode, and temporarily isolate by holding down the control key. This gives a quick workflow for finding and repairing glitches.