# LicPlateNN : License plate detection and recognition

The licplatenn module provides license plate detection and recognition function.

User can use the following code to import the licplatenn module.

var licplatenn = require('licplatenn');

# Support

The following shows licplatenn module APIs available for each permissions.

# licplatenn Object

# licplatenn.detect(videoBuf, attribute)

• videoBuf {Buffer} Video buffer.
• attribute {Object} Video attribute.
• Returns: {Array} License plate info objects array which detectd.

Detect license plate infos in given video buffer.

The video attribute attribute object contains the following members:

• width {Integer} Video width.
• height {Integer} Video height.
• pixelFormat {Integer} Pixel format.

pixelFormat is a integer, can be:

The returned license plate info object contains the following members:

• prob {Number} Probability 0.0 ~ 1.0.
• x0 {Integer} x position of upper left corner.
• y0 {Integer} y position of upper left corner.
• x1 {Integer} x position of lower right corner.
• y1 {Integer} y position of lower right corner.

# licplatenn.identify(videoBuf, attribute, licPlateInfo)

• videoBuf {Buffer} Video buffer.
• attribute {Object} Video attribute.
• licPlateInfo {Object} License plate info object.
• Returns: {String} License plate number.

Identify license plate number of given license plate info.

# Example

This example show how to detect and identify license plate.

var MediaDecoder = require('mediadecoder');
var iosched = require('iosched');
var licplatenn = require('licplatenn');

var image = new MediaDecoder().open('file://./1.jpg');

var fmt = image.srcVideoFormat();
image.destVideoFormat({width: fmt.width, height: fmt.height, fps: 1, pixelFormat: MediaDecoder.PIX_FMT_RGB24, noDrop: false, disable: false});
image.destAudioFormat({disable: true});
image.previewFormat({enable: true, fb: 0, fps: 25, fullscreen: false});

var ol = image.overlay();
var quited = false;

image.on('video', (video) => {
  var buf = new Buffer(video.arrayBuffer);
  var licInfo = licplatenn.detect(buf, {width: fmt.width, height: fmt.height, pixelFormat: licplatenn.PIX_FMT_RGB24});
  ol.clear();
  if (licInfo.length) {
    ol.font(12);
    for (var i = 0; i < licInfo.length; i++) {
      var licNum = licplatenn.identify(buf, {width: fmt.width, height: fmt.height, pixelFormat: licplatenn.PIX_FMT_RGB24}, licInfo[i])
      ol.rect(licInfo[i].x0, licInfo[i].y0, licInfo[i].x1, licInfo[i].y1, MediaDecoder.C_GREEN, 2, 0, false);
      ol.text(licInfo[i].x0, licInfo[i].y0 - 30, licNum, MediaDecoder.C_GREEN);
    }
  }
});

image.on('eof', () => {
  quited = true;
});

image.start();

while (!quited) {
  iosched.poll(); // Event poll.
}

image.close();