code: function BmpEncoder(imgData){
  	this.buffer = imgData.data;
  	this.width = imgData.width;
  	this.height = imgData.height;
  	this.extraBytes = this.width%4;
  	this.rgbSize = this.height*(3*this.width+this.extraBytes);
  	this.headerInfoSize = 40;
  
  	this.data = [];
  	/******************header***********************/
  	this.flag = "BM";
  	this.reserved = 0;
  	this.offset = 54;
  	this.fileSize = this.rgbSize+this.offset;
  	this.planes = 1;
  	this.bitPP = 24;
  	this.compress = 0;
  	this.hr = 0;
  	this.vr = 0;
  	this.colors = 0;
  	this.importantColors = 0;
  }
docs: @author shaozilee
  
  BMP format encoder,encode 24bit BMP
  Not support quality compression