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Vector Corner Pin

Brief Description

This modifier is very similar to the UV Map Generator: It internally generate UV Maps using a motion-vector pass analysis and applies it to the source image. Moreover, the vectors also used to drive a Corner Pin so that it is possible to set keyframes if the vectors make the source image drift too much. The motion vectors influence parameter can control the influence of the motion vectors against the Corner Pin to prevent the vectors from drifting locally too much.


The Vector Corner Pin modifier is very similar to the UV Map generator and shares the same workflow.

In order to place the image to match-move correctly, the Vector Corner Pin offers a Corner Pin widget right in the viewport on which you can move the To Points.


Whenever moving the To Points, a keyframe will be created on the "User To" parameters in the timeline. Each keyframe serves as a new reference frame for the UV maps: at a keyframe, the deformation caused by the UV Map will be pass-through and only the Corner Pin you adjust is used as transformation on the image.

Whenever adding new keyframes or editing keyframes, you need to re-track the UV-Maps in between the previous and next keyframes. To do so, you can use the horizontal toolbar in the viewer contextual interface.


The first 4 buttons are used to launch tracking over different ranges of frames. The next 4 buttons are used to remove keyframes on the Corner Pin. The Motion-Vectors and UV-Maps menus are useful to remove generated files on disk.

When Overwrite Files is left unchecked in the menu, any existing file will be preserved when re-generating, thus skipping computations. Turning it on will force a re-generation of the motion-vectors/UV-Maps.

Changing these parameters require a recomputation of the motion-vectors:

  • Frame Distance
  • Motion Estimation parameters
  • EXR Disk Cache Path
  • Filename Identifier
  • Track Region Mode or Track Region rectangle
  • Motion source

Changing these parameters require a recomputation of the UV-Maps:

  • Any parameters that affect the motion-vectors
  • Any change made on the Corner Pin

Setting new keyframes

When the match-move starts to drift, you can place a new keyframe by moving any To point in the viewport. You will then need to relaunch a track, using the viewer toolbar. Make sure "Overwrite Files" in the UV-Maps settings is checked.

Smoothing the motion

You may want to reduce the strength of the deformation caused by the motion vectors. To do so, the following parameters can be used:

  • Frame Distance: Increase it to compute vectors across a longer range of time so that motion is more smooth. For fast motions, this can lead to drifts

  • UV-Map Blur: Slightly blur the map in order to avoid artefacts. A high blur can lead to drift in areas with complexe motions, such as the border of the lips of a human face

  • Motion-Vectors influence: Reducing it will give more weight to the Corner Pin transformation, reducing the visible deformation applied by the motion vectors.


Parameter / Script Name Type Default Function
Enabled / enabled Boolean On
Motion Estimation / motionEstimation Category -
Motion Source / motionSource Image - The footage that will be used to compute the motion-vectors
Track Region / roi -200, -200, 200, 200 Only pixels within this region will be tracked. This is useful for example if you need to track a small portion of the image. Note that the rectangle should be large enough to enclose all possible position of the pixels throughout the track length
Track Region Mode / roiMode Choice Whole Image The region used to track the pixels. Selecting Track Region and defining a smaller rectangle may improve performances
- Track Region
- Whole Image
EXR Disk Cache Path / cache_path File Path where computed motion vectors and UVMaps are stored. The ${ProjectDir} variable can be used to refer to the directory where the project file is located. If the project is not yet saved, the vectors are stored in a temporary location on your system
Filename Identifier / uv_basename UV-maps and motion vectors files will be named on disk as following with: "uv_" or "mv_", followed by this identifier and ending with informations such as frame distance, reference frame and frame numbering
Frame Distance / frame_distance Float 1 Number of separating frames between a frame and the next when computing motion vectors. A higher value will smooth out jitter. It affects the tracking of motion-vectors and UV-Maps
Use GPU If Available / use_gpu Boolean Off Use CUDA for motion-vectors computation if possible. Results may differ slightly from CPU version and depending on the CUDA driver. It is safer to leave it disabled.
UV-Map Blur / blur Float 0 Smooth the UV-Map as a post-process before applying the UVs. It does not affect the tracking process
Track Red / track_red Boolean On Consider the source image red channel when tracking
Track Green / track_green Boolean On Consider the source image green channel when tracking
Track Blue / track_blue Boolean On Consider the source image blue channel when tracking
Motion Vectors Influence / mv_influence_multiplier Float 1 Motion vectors are most influent when between keyframes on the User To points. To reduce strength of the motion vectors, decrease this value. It does not affect the tracking process.
Supersampling / supersampling Choice x2 The supersampling factor. Higher means more quality and antialiasing but slower to render
- x1
- x2
- x4
- x8
- x16
Filter / filter Choice Inherit The antialiasing algorithm used as reconstruction filter. Note that if the uv map contains offset where 2 source pixels do not end up close-by in the output image, any reconstruction filter would produce incorrect results by mixing pixels that are apart in the source image. The only correct way to antialias in this mode is using a supersampling factor below and set filter to Nearest
- Inherit: Inherit parent layer filter
- None: No interpolation
- Box: Box filter
- Triangle: Bilinear filter
- Hermite: Hermite interpolation filter (smoothstep in glsl)
- Hann
- Hamming
- Blackman
- Gaussian
- Quadratic
- Cubic: General Cubic Filter. Emulates a Gaussian Blurring Filter. This curve is also known as a 'B-Spline' interpolation curve, and is also commonly used for drawing smooth lines through a collection of points. It is also often used for camera and object motions in animations, to produce a smooth flow though the user provided control point
- Spline 16
- Spline 36
- Spline 64
- Spline 100
- Spline 144
- Catmull-Rom
- Mitchell
- Keys
- Keys Sharp
- Sinc
- Jinc
- Kaiser
- Welch
- Parzen
- Bohman
- Cosine
- Bartlett
- Lagrange 3
- Lanczos 2
- Lanczos 2 Sharp
- Lanczos 3
- Lanczos 3 Sharp
- Lanczos 4
- Lanczos 6
From 1 / from_bl Float 2D 0, 0
From 2 / from_br Float 2D 0, 0
From 3 / from_tr Float 2D 0, 0
From 4 / from_tl Float 2D 0, 0
User To 1 / to_bl Float 2D 0, 0
User To 2 / to_br Float 2D 0, 0
User To 3 / to_tr Float 2D 0, 0
User To 4 / to_tl Float 2D 0, 0
Track To 1 / mvToBL Float 2D 0, 0
Track To 2 / mvToBR Float 2D 0, 0
Track To 3 / mvToTR Float 2D 0, 0
Track To 4 / mvToTL Float 2D 0, 0
Algorithm / of_algo Choice Dense Inverse Search
- Dense Inverse Search
- Dual TV L1
Finest Scale / of_dis_finest_scale Float 1 The finest level of the Gaussian pyramid on which the flow is computed (zero level corresponds to the original image resolution). The final flow is obtained by bilinear upscaling.
Patch Size / of_dis_patch_size Float 8 Size of an image patch for matching (in pixels). Normally, default 8x8 patches work well enough in most cases.
Patch Stride / of_dis_patch_stride Float 3 Stride between neighbor patches. Must be less than patch size. Lower values correspond to higher flow quality.
Descent Num. Iterations / of_dis_gradient_descent_iters Float 25 Maximum number of gradient descent iterations in the patch inverse search stage. Higher values may improve quality in some cases.
Refinement Num. Iterations / of_dis_var_refinement_iters Float 5 Number of fixed point iterations of variational refinement per scale. Set to zero to disable variational refinement completely. Higher values will typically result in more smooth and high-quality flow.
Refinement Smoothness Weight / of_dis_var_refinement_alpha Float 20 Weight of the smoothness term
Refinement Gradient Constancy / of_dis_var_refinement_gamma Float 10 Weight of the gradient constancy term
Refinement Color Constancy / of_dis_var_refinement_delta Float 5 Weight of the color constancy term
Robust To Illumination Changes / of_dis_use_mean_propagation Boolean On Whether to use mean-normalization of patches when computing patch distance. It is turned on by default as it typically provides a noticeable quality boost because of increased robustness to illumination variations. Turn it off if you are certain that your sequence doesn't contain any changes in illumination.
Spatial Propagation / of_dis_use_spatial_propagation Boolean On Whether to use spatial propagation of good optical flow vectors. This option is turned on by default, as it tends to work better on average and can sometimes help recover from major errors introduced by the coarse-to-fine scheme employed. Turning this option off can make the output flow field a bit smoother
Time Step (Tau) / of_dualtvl1_tau Float 0.25 Time step of the numerical scheme
Attachment Weight / of_dualtvl1_lambda Float 0.15 Weight parameter for the data term, attachment parameter. This is the most relevant parameter, which determines the smoothness of the output. The smaller this parameter is, the smoother the solutions we obtain. It depends on the range of motions of the images, so its value should be adapted to each image sequence.
Tightness Weight / of_dualtvl1_theta Float 0.15 Link between the attachment and the regularization terms. In theory, it should have a small value in order to maintain both parts in correspondence. The method is stable for a large range of values of this parameter.
Pyramide Size / of_dualtvl1_nscales Float 5 Number of scales used to create the pyramid of images
Num. Warps / of_dualtvl1_warps Float 5 Number of warpings per scale. This ensures the stability of the method. The higher it is, the more accurate it is, but slower
Error Tolerance / of_dualtvl1_epsilon Float 0.01 Stopping criterion threshold used in the numerical scheme, which is a trade-off between precision and running time. A small value will yield more accurate solutions at the expense of a slower convergence.
Inner Iterations / of_dualtvl1_inner_iter Float 30 Iterations number used when filtering outliers
Outer Iterations / of_dualtvl1_outter_iter Float 10 Number of iterations used in the numerical scheme
Scale Step / of_dualtvl1_scale_step Float 0.8 Step between pyramid scales
Median Filter Size / of_dualtvl1_median_filter_size Float 5 Size of the median filter kernel (1 = no filter). Must be 1, 3 or 5