--- title: "How To: Measure Part Area from a Camera Image" product: "LumiScan Area Detector" component: "lumiscan-area-detector" version: "1.2.0" display_version: "1.2.0.6" latest_version: true language: "en" url: "https://docs.hdvisionsystems.com/en/lumiscan-area-detector/1.2.0/how-tos/measure-part-area-from-a-camera-image.html" --- # How To: Measure Part Area from a Camera Image – LumiScan Area Detector Start to finish: get a real area measurement out of a live camera, and make it survive a restart. ## Before you start - LumiScan Cam Driver is installed and publishing an image, for example at `hdvisionsystems/lumiscan-cam-driver/camera1/output/image`. - LumiScan Area Detector is installed, and `system/modules` lists `module-1`. On ctrlX OS it is also licensed, see [Requirements](https://docs.hdvisionsystems.com/en/lumiscan-area-detector/1.2.0/lumiscan-area-detector/requirements.html). - The parts are in front of the camera, in the lighting the installation will actually use. ## Step 1: see what is found with the defaults ``` module-1/detect-area/input/input-image-address = hdvisionsystems/lumiscan-cam-driver/camera1/output/image write module-1/detect-area/execute ``` Check `output/status-code` is `1`, then read `output/result`. Look at `blob_count`: too many means noise is being counted, zero means nothing matched. The areas are already real pixel counts. What the next step changes is how the regions are found. ## Step 2: commission the level The one setting that decides whether this works is the brightness a pixel must exceed. Do not guess it - measure the picture: ``` system/analyse-scene/input/input-image-address = "hdvisionsystems/lumiscan-cam-driver/camera1/output/image" write system/analyse-scene/execute read system/analyse-scene/output/recommended-settings read system/analyse-scene/output/histogram ``` `recommended-settings` gives you a level, which end is the part, and whether to fill holes. `histogram` is how you check it: the level wants to sit in the valley between the part’s hump and the background’s. Two humps with a gap means the picture separates cleanly; one hump means no level will save it and the lighting needs fixing instead. Then set it on the module: ``` module-1/detect-area/input/method-specific/fixed/level = 128 write module-1/detect-area/execute ``` If the parts are darker than the background, add: ``` module-1/detect-area/input/detect-dark = true ``` ## Step 3: stop counting noise Look at the smallest entries in `blobs`. The app reports every region it separated - there is no area window to raise - so noise and dust are dealt with in one of two places: - **At the level.** Raising `method-specific/fixed/level` until noise stops crossing the threshold is the better fix, because those regions then cost nothing to find. - **In your control program.** Ignore any `blobs[]` entry whose `area` is below what a part can be. A quarter of the area of the smallest part you care about is a good starting point. That decision belongs to you: only you know what a part is. ## Step 4: check the number against something you know Measure a part whose real area you know - or count its pixels once in an image viewer - and compare it against `blobs[0].area`. They should agree closely. If the measurement is consistently low, the threshold is cutting into the part: lower `method-specific/fixed/level`, and try `detect-dark` if the part is the darker of the two. ## Step 5: make it permanent ``` system/save-module-inputs/input/module-id = module-1 write system/save-module-inputs/execute write system/save-current-modules/execute ``` Both should report `1`. The module and its settings now survive a restart. ## Step 6: run it from a control program Per cycle: 1. Write to `module-1/detect-area/execute`. 2. Read `module-1/detect-area/output/status-code`. 3. If negative, the run failed - read `output/status-text` and do not use the result. 4. If `1`, read `output/result` and act on `total_area`, or on `blob_count` for a presence check. Read the outputs **before** triggering the next `execute`: a run empties them as it starts. ## If the numbers look wrong Problems are described step by step in [Troubleshooting](https://docs.hdvisionsystems.com/en/lumiscan-area-detector/1.2.0/troubleshooting.html): - [The measured area is larger or smaller than the part](https://docs.hdvisionsystems.com/en/lumiscan-area-detector/1.2.0/troubleshooting.html#faq-area-wrong) - much larger, consistently short, or a part with a hole - [Many tiny regions are reported](https://docs.hdvisionsystems.com/en/lumiscan-area-detector/1.2.0/troubleshooting.html#faq-tiny-regions) - [One part is reported as several regions](https://docs.hdvisionsystems.com/en/lumiscan-area-detector/1.2.0/troubleshooting.html#faq-part-split) - [Nothing is found, or the result is empty](https://docs.hdvisionsystems.com/en/lumiscan-area-detector/1.2.0/troubleshooting.html#faq-nothing-found) - [The reading drifts with the lighting, or no level works](https://docs.hdvisionsystems.com/en/lumiscan-area-detector/1.2.0/troubleshooting.html#faq-reading-drifts)