tiff

读取TIFF文件中的 idf和de

##使用示例
~~~javascript
import Tiff from 'ljw-tiff'


var readerBuffer = new FileReader()
readerBuffer.readAsArrayBuffer(file)

new Promise((resolve, reject) => {
readerBuffer.onload = (e) => {
const TiffObj = new Tiff()
const idfs = TiffObj.readTiffInfo(e.currentTarget.result)
resolve(idfs)
}
}).then(res => {
console.log(res)
//[
// {DEs:[
// {start: 10, tag16: "fe", tag: 254, type: 4, len: 1, trueValue:[0]},
// {start: 22, tag16: "100", tag: 256, type: 3, len: 1, trueValue:[100]},
// {start: 34, tag16: "101", tag: 257, type: 3, len: 1, trueValue:[100]},
// ...
// ],startOffset:8,endOffset:278}
//]
})

~~~

###DE的type类型
~~~javascript
/**
* tiff中的类型
1 = BYTE 8-bit unsigned integer.
2 = ASCII 8-bit byte that contains a 7-bit ASCII code; the last byte
must be NUL (binary zero).
3 = SHORT 16-bit (2-byte) unsigned integer.
4 = LONG 32-bit (4-byte) unsigned integer.
5 = RATIONAL Two LONGs: the first represents the numerator
6 = SBYTE An 8-bit signed (twos-complement) integer.
7 = UNDEFINED An 8-bit byte that may contain anything, depending on
the definition of the field.
8 = SSHORT A 16-bit (2-byte) signed (twos-complement) integer.
9 = SLONG A 32-bit (4-byte) signed (twos-complement) integer.
10 = SRATIONAL Two SLONG’s: the first represents the numerator of a
fraction, the second the denominator.
11 = FLOAT Single precision (4-byte) IEEE format.
12 = DOUBLE Double precision (8-byte) IEEE format.
* @type {({len: number, name: string}|{len: number, name: string})[]}
*/
~~~