How To: Measure Part Area from a Camera Image

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.

  • 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: