var f = new File('c:\yourpath\\file.psd');

f.readonly = true;
f.encoding = "BINARY";
f.open ("r");
var ln = 4; // 4 pro PSD - 8 pro PSB


/*alert(layersCount ());
alert(getLayerInfoLength ());
alert(getLayerInfoLength2 ());
alert(getLayerInfoLength2 ());*/

f.close();

function getDecimalValue(str){
    return (parseInt(convertDecimalToHex(stringToBytes (str)),16));
}

function stringToBytes ( str ) {
  var ch, st, re = [];
  for (var i = 0; i < str.length; i++ ) {
    ch = str.charCodeAt(i);  // get char
    st = [];                 // set up "stack"
    do {
      st.push( ch & 0xFF );  // push byte to stack
      ch = ch >> 8;          // shift value down by 1 byte
    }
    while ( ch );
    // add stack contents to result
    // done because chars have "wrong" endianness
    re = re.concat( st.reverse() );
  }
  // return an array of bytes
  return re;
}

function convertDecimalToHex (str){ //funguje mění decimální čísla na hex
    var re=0x00;
    for (var i =0;i<str.length;i++){
        re+=str[i].toString(16);

    }
    return re;
}


////////////////////////////
// Main sections
////////////////////////////

function seekHeader(){
     f.seek(0);
}

function seekColorMode(){
    f.seek(26);
}

function seekImageResources(){
    seekColorMode();
    f.seek(getDecimalValue(f.read(ln)),1)
}

function seekLayerAndMask(){
    seekImageResources ();
    f.seek(getDecimalValue(f.read(ln)),1)
}

function seekImageData(){
    seekLayerAndMask ();
    f.seek(getDecimalValue(f.read(ln)),1)
}

//////////////////////////////////

function getLayerInfoLength(){
    seekLayerAndMask ();
    f.seek(ln,1); //poskočí dovnitř, jinak by četl délku sekce LayerAndMask
    var re = getDecimalValue(f.read(ln))
    if(re % 2 == 1){
        return re+1;
    }
    return re;
}

function getLayerInfoLength2(){
    f.seek(ln,1);
    var re = getDecimalValue(f.read(ln))
    if(re % 2 == 1){
        return re+1;
    }
    return re;
}


////////////////////////
// Utility
////////////////////////

function layersCount(){
    seekLayerAndMask ();
    f.seek(ln*2,1);
    return getDecimalValue(f.read(2));
}