frigate/docs/docs/configuration/license_plate_recognition.md

id, title

id	title
license_plate_recognition	License Plate Recognition (LPR)

Frigate can recognize license plates on vehicles and automatically add the detected characters to the recognized_license_plate field or a known name as a sub_label to tracked objects of type car. A common use case may be to read the license plates of cars pulling into a driveway or cars passing by on a street.

LPR works best when the license plate is clearly visible to the camera. For moving vehicles, Frigate continuously refines the recognition process, keeping the most confident result. However, LPR does not run on stationary vehicles.

When a plate is recognized, the recognized name is:

• Added as a sub_label (if known) or the recognized_license_plate field (if unknown) to a tracked object.
• Viewable in the Review Item Details pane in Review (sub labels).
• Viewable in the Tracked Object Details pane in Explore (sub labels and recognized license plates).
• Filterable through the More Filters menu in Explore.
• Published via the frigate/events MQTT topic as a sub_label (known) or recognized_license_plate (unknown) for the car tracked object.

Model Requirements

Users running a Frigate+ model (or any custom model that natively detects license plates) should ensure that license_plate is added to the list of objects to track either globally or for a specific camera. This will improve the accuracy and performance of the LPR model.

Users without a model that detects license plates can still run LPR. Frigate uses a lightweight YOLOv9 license plate detection model that runs on your CPU. In this case, you should not define license_plate in your list of objects to track.

:::note

In the default mode, Frigate's LPR needs to first detect a car before it can recognize a license plate. If you're using a dedicated LPR camera and have a zoomed-in view where a car will not be detected, you can still run LPR, but the configuration parameters will differ from the default mode. See the Dedicated LPR Cameras section below.

:::

Minimum System Requirements

License plate recognition works by running AI models locally on your system. The models are relatively lightweight and run on your CPU. At least 4GB of RAM is required.

Configuration

License plate recognition is disabled by default. Enable it in your config file:

lpr:
  enabled: True

Like other enrichments in Frigate, LPR must be enabled globally to use the feature. You can disable it for specific cameras at the camera level:

cameras:
  driveway:
    ...
    lpr:
      enabled: False

For non-dedicated LPR cameras, ensure that your camera is configured to detect objects of type car, and that a car is actually being detected by Frigate. Otherwise, LPR will not run.

Like the other real-time processors in Frigate, license plate recognition runs on the camera stream defined by the detect role in your config. To ensure optimal performance, select a suitable resolution for this stream in your camera's firmware that fits your specific scene and requirements.

Advanced Configuration

Fine-tune the LPR feature using these optional parameters:

Detection

• detection_threshold: License plate object detection confidence score required before recognition runs.
  • Default: 0.7
  • Note: This is field only applies to the standalone license plate detection model, min_score should be used to filter for models that have license plate detection built in.
• min_area: Defines the minimum area (in pixels) a license plate must be before recognition runs.
  • Default: 1000 pixels. Note: this is intentionally set very low as it is an area measurement (length x width). For reference, 1000 pixels represents a ~32x32 pixel square in your camera image.
  • Depending on the resolution of your camera's detect stream, you can increase this value to ignore small or distant plates.

Recognition

• recognition_threshold: Recognition confidence score required to add the plate to the object as a recognized_license_plate and/or sub_label.
  • Default: 0.9.
• min_plate_length: Specifies the minimum number of characters a detected license plate must have to be added as a recognized_license_plate and/or sub_label to an object.
  • Use this to filter out short, incomplete, or incorrect detections.
• format: A regular expression defining the expected format of detected plates. Plates that do not match this format will be discarded.
  • "^[A-Z]{1,3} [A-Z]{1,2} [0-9]{1,4}$" matches plates like "B AB 1234" or "M X 7"
  • "^[A-Z]{2}[0-9]{2} [A-Z]{3}$" matches plates like "AB12 XYZ" or "XY68 ABC"
  • Websites like https://regex101.com/ can help test regular expressions for your plates.

Matching

• known_plates: List of strings or regular expressions that assign custom a sub_label to car objects when a recognized plate matches a known value.
  • These labels appear in the UI, filters, and notifications.
  • Unknown plates are still saved but are added to the recognized_license_plate field rather than the sub_label.
• match_distance: Allows for minor variations (missing/incorrect characters) when matching a detected plate to a known plate.
  • For example, setting match_distance: 1 allows a plate ABCDE to match ABCBE or ABCD.
  • This parameter will not operate on known plates that are defined as regular expressions. You should define the full string of your plate in known_plates in order to use match_distance.

Image Enhancement

• enhancement: A value between 0 and 10 that adjusts the level of image enhancement applied to captured license plates before they are processed for recognition. This preprocessing step can sometimes improve accuracy but may also have the opposite effect.
  • Default: 0 (no enhancement)
  • Higher values increase contrast, sharpen details, and reduce noise, but excessive enhancement can blur or distort characters, actually making them much harder for Frigate to recognize.
  • This setting is best adjusted at the camera level if running LPR on multiple cameras.
  • If Frigate is already recognizing plates correctly, leave this setting at the default of 0. However, if you're experiencing frequent character issues or incomplete plates and you can already easily read the plates yourself, try increasing the value gradually, starting at 5 and adjusting as needed. To preview how different enhancement levels affect your plates, use the debug_save_plates configuration option (see below).

Debugging

• debug_save_plates: Set to True to save captured text on plates for debugging. These images are stored in /media/frigate/clips/lpr, organized into subdirectories by <camera>/<event_id>, and named based on the capture timestamp.
  • These saved images are not full plates but rather the specific areas of text detected on the plates. It is normal for the text detection model to sometimes find multiple areas of text on the plate. Use them to analyze what text Frigate recognized and how image enhancement affects detection.
  • Note: Frigate does not automatically delete these debug images. Once LPR is functioning correctly, you should disable this option and manually remove the saved files to free up storage.

Configuration Examples

These configuration parameters are available at the global level of your config. The only optional parameters that should be set at the camera level are enabled and min_area.

lpr:
  enabled: True
  min_area: 1500 # Ignore plates with an area (length x width) smaller than 1500 pixels
  min_plate_length: 4 # Only recognize plates with 4 or more characters
  known_plates:
    Wife's Car:
      - "ABC-1234"
      - "ABC-I234" # Accounts for potential confusion between the number one (1) and capital letter I
    Johnny:
      - "J*N-*234" # Matches JHN-1234 and JMN-I234, but also note that "*" matches any number of characters
    Sally:
      - "[S5]LL 1234" # Matches both SLL 1234 and 5LL 1234
    Work Trucks:
      - "EMP-[0-9]{3}[A-Z]" # Matches plates like EMP-123A, EMP-456Z

lpr:
  enabled: True
  min_area: 4000 # Run recognition on larger plates only (4000 pixels represents a 63x63 pixel square in your image)
  recognition_threshold: 0.85
  format: "^[A-Z]{2} [A-Z][0-9]{4}$" # Only recognize plates that are two letters, followed by a space, followed by a single letter and 4 numbers
  match_distance: 1 # Allow one character variation in plate matching
  known_plates:
    Delivery Van:
      - "RJ K5678"
      - "UP A1234"
    Supervisor:
      - "MN D3163"

Dedicated LPR Cameras

Dedicated LPR cameras are single-purpose cameras with powerful optical zoom to capture license plates on distant vehicles, often with fine-tuned settings to capture plates at night.

Users with a dedicated LPR camera can run Frigate's LPR by specifying a camera type of lpr in the camera configuration. An example config for a dedicated LPR camera might look like this:

# LPR global configuration
lpr:
  enabled: True
  min_plate_length: 4
  detection_threshold: 0.7 # change if necessary

# Dedicated LPR camera configuration
cameras:
  dedicated_lpr_camera:
    type: "lpr" # required to use dedicated LPR camera mode
    lpr:
      enabled: True
      expire_time: 3 # optional, default
      enhancement: 3 # optional, enhance the image before trying to recognize characters
    ffmpeg: ...
    detect:
      enabled: False # optional, disable Frigate's standard object detection pipeline
      fps: 5 # keep this at 5, higher values are unnecessary for dedicated LPR mode and could overwhelm the detector
      width: 1920
      height: 1080
    motion:
      threshold: 30
      contour_area: 60 # use an increased value here to tune out small motion changes
      improve_contrast: false
      mask: 0.704,0.007,0.709,0.052,0.989,0.055,0.993,0.001 # ensure your camera's timestamp is masked
    record:
      enabled: True # disable recording if you only want snapshots
    review:
      detections:
        enabled: True
        retain:
          default: 7

The camera-level type setting tells Frigate to treat your camera as a dedicated LPR camera. Setting this option bypasses Frigate's standard object detection pipeline so that a car does not need to be detected to run LPR. This dedicated LPR pipeline does not utilize defined zones or object masks, and the license plate detector is always run on the full frame whenever motion activity occurs. If a plate is found, a snapshot at the highest scoring moment is saved as a car object, visible in Explore and searchable by the recognized plate via Explore's More Filters.

An optional config variable for dedicated LPR cameras only, expire_time, can be specified under the lpr configuration at the camera level to change the time it takes for Frigate to consider a previously tracked plate as expired.

:::note

When using type: "lpr" for a camera, a non-standard object detection pipeline is used. Any detected license plates on dedicated LPR cameras are treated similarly to manual events in Frigate. Note that for car objects with license plates:

• Review items will always be classified as a detection.
• Snapshots will always be saved.
• Tracked objects are retained according to your retain settings for record and snapshots.
• Zones and object masks cannot be used.
• Debug view may not show license_plate bounding boxes, even if you are using a Frigate+ model for your standard object detection pipeline.
• The frigate/events MQTT topic will not publish tracked object updates, though frigate/reviews will if recordings are enabled.

:::

Best practices for using Dedicated LPR camera mode

• Tune your motion detection and increase the contour_area until you see only larger motion boxes being created as cars pass through the frame (likely somewhere between 50-90 for a 1920x1080 detect stream). Increasing the contour_area filters out small areas of motion and will prevent excessive resource use from looking for license plates in frames that don't even have a car passing through it.
• Disable the improve_contrast motion setting, especially if you are running LPR at night and the frame is mostly dark. This will prevent small pixel changes and smaller areas of motion from triggering license plate detection.
• Ensure your camera's timestamp is covered with a motion mask so that it's not incorrectly detected as a license plate.
• While not strictly required, it may be beneficial to disable standard object detection on your dedicated LPR camera (detect --> enabled: False). If you've set the camera type to "lpr", license plate detection will still be performed on the entire frame when motion occurs.
• If multiple tracked objects are being produced for the same license plate, you can tweak the expire_time to prevent plates from being expired from the view as quickly.
• You may need to change your camera settings for a clearer image or decrease your global recognition_threshold config if your plates are not being accurately recognized at night.

FAQ

Why isn't my license plate being detected and recognized?

Ensure that:

• Your camera has a clear, human-readable, well-lit view of the plate. If you can't read the plate's characters, Frigate certainly won't be able to, even if the model is recognizing a license_plate. This may require changing video size, quality, or frame rate settings on your camera, depending on your scene and how fast the vehicles are traveling.
• The plate is large enough in the image (try adjusting min_area) or increasing the resolution of your camera's stream.
• Your enhancement level (if you've changed it from the default of 0) is not too high. Too much enhancement will run too much denoising and cause the plate characters to become blurry and unreadable.

If you are using a Frigate+ model or a custom model that detects license plates, ensure that license_plate is added to your list of objects to track. If you are using the free model that ships with Frigate, you should not add license_plate to the list of objects to track.

Recognized plates will show as object labels in the debug view and will appear in the "Recognized License Plates" select box in the More Filters popout in Explore.

If you are still having issues detecting plates, start with a basic configuration and see the debugging tips below.

Can I run LPR without detecting car objects?

In normal LPR mode, Frigate requires a car to be detected first before recognizing a license plate. If you have a dedicated LPR camera, you can change the camera type to "lpr" to use the Dedicated LPR Camera algorithm. This comes with important caveats, though. See the Dedicated LPR Cameras section above.

How can I improve detection accuracy?

• Use high-quality cameras with good resolution.
• Adjust detection_threshold and recognition_threshold values.
• Define a format regex to filter out invalid detections.

Does LPR work at night?

Yes, but performance depends on camera quality, lighting, and infrared capabilities. Make sure your camera can capture clear images of plates at night.

How can I match known plates with minor variations?

Use match_distance to allow small character mismatches. Alternatively, define multiple variations in known_plates.

How do I debug LPR issues?

• View MQTT messages for frigate/events to verify detected plates.

• If you are using a Frigate+ model or a model that detects license plates, watch the debug view (Settings --> Debug) to ensure that license_plate is being detected with a car.

• Watch the debug view to see plates recognized in real-time. For non-dedicated LPR cameras, the car label will change to the recognized plate when LPR is enabled and working.

• Adjust detection_threshold and recognition_threshold settings per the suggestions above.

• Enable debug_save_plates to save images of detected text on plates to the clips directory (/media/frigate/clips/lpr).

• Enable debug logs for LPR by adding frigate.data_processing.common.license_plate: debug to your logger configuration. These logs are very verbose, so only enable this when necessary.

  logger:
    default: info
    logs:
      frigate.data_processing.common.license_plate: debug
  

Will LPR slow down my system?

LPR runs on the CPU, so performance impact depends on your hardware. Ensure you have at least 4GB RAM and a capable CPU for optimal results. If you are running the Dedicated LPR Camera mode, resource usage will be higher compared to users who run a model that natively detects license plates. Tune your motion detection settings for your dedicated LPR camera so that the license plate detection model runs only when necessary.