> For the complete documentation index, see [llms.txt](https://docs.augelab.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.augelab.com/function-blocks/blocks-reference/detections-shapes/roi-processing/image-roi-polygon.md). # Image ROI Polygon This function block lets you draw a polygon directly on an image to define a custom region of interest (ROI). Use it to select irregular shapes, edit vertices interactively, and output both the cropped image inside the polygon and the polygon coordinates for downstream processing. ## đŸ“Ĩ Inputs * `Image Any` The image to display and annotate. Connect any image-producing block here so you can draw the polygon on a live preview. ## 📤 Outputs * `Image Any` The cropped image corresponding to the polygon area. If no polygon is defined this output may be empty. * `Polygon` The polygon coordinates returned as a contour/shape list suitable for use by other blocks. ## 🕹ī¸ Controls * `Left Click` Add a vertex at the clicked location. * `Drag` Click and drag an existing vertex to reposition it. * `U` Undo the last added vertex. * `C` Clear all vertices and start again. * `Overlay Preview` Visual markers and fill are shown while editing so you can see the polygon, vertices and the selection area in real time. ## ⚙ī¸ Running mechanism * Connect an image source to the `Image Any` input and run the scenario once to populate the preview. * Draw the polygon by clicking to add vertices. The overlay updates immediately. * Use drag and keyboard shortcuts to refine the shape. * When a polygon is present the block produces a cropped image (tight bounding rectangle of the polygon) and the polygon coordinate list on each evaluation. ## ✨ Features * Interactive polygon drawing with vertex editing. * Undo/clear shortcuts for quick corrections. * Visual overlay with vertex highlights while hovering or dragging. * Outputs both a cropped image and precise polygon coordinates. * Supports non-rectangular and multi-point ROIs for irregular objects. ## 📝 Usage tips * Draw at least three points to form a filled polygon; fewer points will not yield a valid ROI crop. * After drawing, run downstream blocks to process the cropped image or polygon coordinates. * Use the drag feature to fine-tune vertex positions for accurate measurements. ## 💡 Tips and Tricks * Preview larger images by connecting the output to `Show Image` so you can draw more precisely on a separate viewer. * If you need multiple ROIs in one image, use `Image ROI Polygon Multi` to store several polygon selections and then feed each to processing blocks. * Combine with `Get ROI` or `Image ROI Select` if you prefer rectangular crops first, then refine with polygon for complex shapes. * Use `Apply Mask` after this block to mask the original image with the polygon and feed that masked image into analysis blocks. * Feed the cropped polygon image into detection or analysis blocks such as `Find Object`, `Object Detection`, `Mask Detection`, `Histogram On Line` or `Color Density Percentage` to focus processing on the selected area. * If the image is too large to draw comfortably, add `Image Resizer` or `Image Resize` before this block; remember that resizing changes pixel coordinates used by downstream geometry-sensitive blocks. * Save selected ROIs with `Image Logger`, `Image Write` or `Multi Image Write` for dataset collection or later review. ## 🛠ī¸ Troubleshooting * No image displayed: make sure an image-producing block is connected to `Image Any` and run once to populate the preview. * ROI not produced: ensure you have at least three vertices; fewer points cannot form a filled polygon. * Polygon appears misplaced after resizing upstream images: either draw at the final resolution or insert `Image Resizer` consistently in the pipeline so coordinates remain aligned. * Need exact coordinates for other blocks: use the `Polygon` output (coordinate list) and verify with a preview via `Show Image` or re-run after adjustments.