Image Masking

Define regions to exclude from PIV processing. Masked regions produce zero-valued vectors in output fields.

Masking Modes

Two modes are available, selected from the Masking Mode dropdown. Toggle Apply Mask for PIV to activate masking during processing.

Mode	YAML Value	Description	Storage
Polygon	file	Draw arbitrary polygons on the image. Multiple polygons combined into one mask.	`mask_CamN.mat` per camera
Pixel Border	rectangular	Mask fixed pixel borders from each image edge.	`config.yaml`

Polygon Mask Editor

Interactive canvas for drawing mask regions on PIV images. Supports multiple polygons, edge snapping, and a magnifier for precise placement.

Drawing Workflow

Select source path, camera, and image index, then click Load Image.
Click on the image to place polygon vertices (shown in green).
After 3+ points, click the red starting point to close the polygon. It turns orange and a new polygon starts automatically.
Repeat to add more polygons. All closed polygons combine into a single mask.

Edge Snapping

Click in the padding area outside the image to snap points to the nearest edge or corner. The magnifier border turns orange in the snap zone.

Magnifier

2.5x zoomed view following the cursor with crosshairs at the exact click position. Toggle via the magnifier button in the toolbar.

Toolbar Controls

Button	Action
New Polygon	Start a fresh polygon (auto-finishes current)
Undo Point	Remove the last point from active polygon
Delete	Delete the currently selected polygon
Prev / Next	Navigate between polygons
Magnifier	Toggle 2.5x zoom tool
Save PNG	Download mask as PNG image
Clear Mask	Remove all polygons and reset

Auto-save: Masks save automatically to mask_CamN.mat when you complete, delete, or clear a polygon. No manual save needed.

Pixel Border Mode

Mask fixed rectangular regions from each image edge. Enter pixel values for top, bottom, left, and right. The preview updates live with a red overlay showing excluded regions.

Values are saved automatically to config.yaml. Same settings apply to all cameras.

masking:
  enabled: true
  mode: rectangular
  rectangular:
    top: 64
    bottom: 64
    left: 0
    right: 0

Mask Storage

Format	Location	Contents
Standard images	source_path/mask_Cam1.mat	Binary mask + polygon vertices + names
LaVision .set files	{name}_data/mask_{name}_Cam1.mat	Same contents, in sibling directory

Per-camera masks: Each camera has its own mask file. In stereo setups, create separate masks for Cam1 and Cam2. Switch cameras with the Camera dropdown; the correct mask loads automatically.

Export

Polygon masks auto-save as .mat files for PIV processing. The Save PNG toolbar button exports a full-resolution binary image for documentation.

YAML Reference

masking:
  enabled: true                      # Toggle masking for PIV
  mode: file                         # 'file' (polygon) or 'rectangular' (pixel border)
  mask_file_pattern: mask_Cam%d.mat  # %d = camera number
  mask_threshold: 0.01               # Fraction of window that must be masked
  rectangular:
    top: 0
    bottom: 0
    left: 0
    right: 0

GUI Control	YAML Field	Values
Apply Mask for PIV	masking.enabled	true / false
Masking Mode	masking.mode	'file' or 'rectangular'
Top / Bottom / Left / Right	masking.rectangular.*	integer >= 0 (pixels)
Mask file pattern	masking.mask_file_pattern	String with %d for camera
Mask threshold	masking.mask_threshold	float (default 0.01)

Next: Pre-Processing Filters

Apply temporal and spatial filters to enhance images before PIV processing.

Continue to Pre-Processing