Image ROI Polygon

This function block lets you draw a polygon directly on an image to define a region of interest (ROI). Use left mouse clicks to add points, then extract the cropped polygon area or a polygon shape for downstream processing.

📥 Inputs

Input Image Input socket that accepts any image to draw the polygon on.

📤 Outputs

Image Any Output socket that provides the cropped image inside the drawn polygon (or None if no polygon defined).

Polygon Output socket that provides the polygon point list as a shape value suitable for other ROI-aware blocks.

🕹️ Controls

Interactive Image Area Click on the image to add polygon vertices. The interactive area also shows visual feedback (points, connecting lines and a translucent highlight of the polygon).

U Press this key to undo the last added point.

C Press this key to clear all points and start over.

🎨 Features

• Visual point/edge drawing with immediate feedback: points and connecting lines are drawn on the image as you add vertices.

• Highlighted polygon area overlay for quick preview of the selected ROI.

• Returns both the cropped image inside the polygon and the polygon coordinates as an output shape for further processing.

• Supports serialization: polygon points are kept when saving/loading the scenario so you can restore your ROI.

📝 Usage Instructions

1. Connect an image-producing block to Input Image.

2. Run once so the image is visible in the interactive area.

3. Left-click on the image to add polygon vertices in order.

4. Use U to undo the last point or C to clear all points.

5. After defining the polygon, the block outputs the cropped polygon image on Image Any and the polygon coordinates on Polygon.

📊 Evaluation

When evaluated, the block updates the interactive image preview and, if a polygon exists, outputs:

• the cropped polygon image (tight bounding box of the polygon), and

• the polygon coordinates as a shape list ready for downstream blocks.

If no polygon is drawn the Image Any output will be None.

💡 Tips and Tricks

• To visually inspect the selected ROI in larger detail, send the Image Any output to the Show Image block.

• If you need multiple crop areas, use the Image ROI Polygon Multi block to define and manage several polygons.

• To quickly define a rectangular ROI instead of a polygon, combine this block with Image ROI Select or Image ROI for faster rectangle-based cropping.

• Use the polygon coordinates with Apply Mask to mask the original image while preserving full canvas size (useful when you want to keep image alignment).

• Send the cropped ROI to analysis or detection blocks like Find Object or Contour to Image to focus processing only inside the selected area.

• When saving examples or records, attach the cropped output to Image Logger or Image Write to keep dataset images of your ROI.

• If you need a fixed image size for downstream models, add Image Resize after the crop to normalize dimensions.

🛠️ Troubleshooting

• No image visible in the interactive area: ensure an image-producing block is connected to Input Image and run once to populate the preview.

• Polygon not producing an output: make sure at least two points are defined; the block only produces a crop when a polygon is formed.

• Cropped area appears empty or transparent: verify the polygon was drawn within image bounds and that the source image is not all zeros.

• Saved project loses polygon points: confirm the project was saved after drawing (this block serializes the point list, but you must save the scenario to persist it).