Image ROI Circle

This function block lets you create a single editable circular region of interest (ROI) on an image. Use the interactive canvas to draw, move and resize the circle. The block returns the cropped circular image and a circle shape (center and radius) that you can pass to other blocks.

📥 Inputs

Image Image to crop and to edit the circle overlay on (grayscale or color).

📤 Outputs

Image Cropped image containing the circular area (background outside circle masked out).

Circle Circle shape describing the selected ROI as center and radius (useful for geometry-aware blocks).

🕹️ Controls

ROI Canvas Interactive image area where you create and edit the circle by mouse.

Create by Drag Click-and-drag on the canvas to create a new circle.

Move Center Drag the circle center to reposition the ROI.

Resize Radius Drag the radius handle to change the circle size.

Clear (C) Press the C key to clear the current circle and start over.

⚙️ Running mechanism

• The block displays the provided image on the interactive canvas and overlays the current circle (if set).

• While running, the canvas listens for mouse drag and move events to create, move or resize the circle.

• Once a valid circle exists, the block produces the cropped circular image (masked) and a shape output containing center and radius values.

• If the circle is not defined or radius is zero the block outputs None for both sockets so downstream blocks can handle the absence of a ROI.

✨ Features

• Intuitive click-and-drag interaction to create an ROI.

• Separate handles for moving the center and resizing the radius.

• Immediate visual feedback with a colored overlay and handle highlighting.

• Outputs both the masked crop and a reusable shape description.

📝 Usage instructions

1. Connect an image-producing block to the Image input and run once so the image appears on the canvas.

2. Click and drag on the ROI Canvas to create a circle.

3. Drag the circle center to move it or drag the radius handle to resize.

4. Press C to clear and redraw if needed.

5. Use the Image and Circle outputs to send the crop or shape to other blocks.

💡 Tips and Tricks

• Preview the selected crop in a larger window with Show Image for a closer inspection before exporting.

• If your source image is large, use Image Resize before this block to speed interaction and ensure the ROI fits the workspace.

• Use Apply Mask to combine the circular mask with other images or to overlay the mask result on a different background.

• To select more complex or multiple regions, consider using Image ROI Select or Image ROI Polygon Multi and then refine with this circular ROI if needed.

• Save captured crops directly using Image Logger or Image Write for record keeping or downstream processing.

• Preprocess noisy inputs with Blur or Image Threshold so the visual region aligns better with your detection or measurement workflows.

• Combine circle outputs with measurement or analysis blocks (for example shape-analysis or detectors) by passing the Circle shape where supported.

🛠️ Troubleshooting

• No image visible on the canvas: ensure the upstream block is producing an image and run the scenario once so the image is loaded.

• Outputs are None: circle center or radius is undefined, or radius is effectively zero. Redraw the circle.

• Circle appears off or too small: try resizing the canvas via upstream Image Resize or redraw the circle at a larger scale.

• Interaction feels unresponsive: confirm the image was provided at least once and that the canvas shows the image; re-run the block if needed.