go语言实现将重要数据写入图片中

原理:将数据的二进制形式写入图像红色通道数据二进制的低位
只支持png格式的输出
写入数据
go run shadow.go -in="c.jpg" -data="hide me" -out="out.png"
读取数据
go run shadow.go -in="out.png"

package main
import (
    "errors"
    "flag"
    "fmt"
    "image"
    "image/color"
    _ "image/jpeg"
    "image/png"
    "log"
    "math"
    "os"
)
var FLAG = [4]byte{0x13, 0x14, 0x52, 0x00} //shadow flag.
//byte to 8 bits
func Byte2bits(b byte) (a [8]byte) {
    var c uint8 = 7
    var i uint8
    for i = 0; i < 8; i++ {
        a[i] = b >> (c - i) & 1
    }
    return
}
//8 bits to byte.
func Bits2Byte(a [8]byte) (b byte) {
    for i := 0; i < 8; i++ {
        b += a[i] * uint8(math.Pow(2, float64(7-i)))
    }
    return
}
//uint32 to 4 bytes.
func Uint32ToBytes(i uint32) (b [4]byte) {
    b[0] = uint8(i >> 24)
    b[1] = uint8(i >> 16 & 0xffff)
    b[2] = uint8(i >> 8 & 0xff)
    b[3] = uint8(i & 0xff)
    return
}
//4 bytes to uint32.
func Bytes2Uint32(b [4]byte) (i uint32) {
    var j uint32
    for ; j < 4; j++ {
        i += uint32(b[j]) << (24 - j*8)
    }
    return
}
func BuildShadowHeader(length uint32) (b [8]byte) {
    var i int
    for ; i < 4; i++ {
        b[i] = FLAG[i]
    }
    a := Uint32ToBytes(length)
    for ; i < 8; i++ {
        b[i] = a[i-4]
    }
    return
}
func WriteShadow(b []byte, im image.Image) (out image.Image, err error) {
    max := im.Bounds().Max.X*im.Bounds().Max.Y/8 - 64
    b_len := len(b)
    if len(b) > max {
        return nil, errors.New("image does not have enough space for shadow.")
    }
    head := BuildShadowHeader(uint32(b_len))
    var bb byte
    var bs [8]byte
    var i int
    out, err = SetImage(im, func(index, x, y int, in, out image.Image) {
        rgba := readRGBAColor(im.At(x, y))
        if index < b_len*8+64 {
            if index < 64 {
                bb = head[index/8]
            } else {
                bb = b[index/8-8]
            }
            bs = Byte2bits(bb)
            i = index % 8
            if bs[i] != rgba.R&1 {
                if bs[i] == 0 {
                    rgba.R -= 1
                } else {
                    rgba.R += 1
                }
            }
        }
        if v := out.(*image.RGBA); v != nil {
            v.SetRGBA(x, y, rgba)
        }
    })
    if err != nil {
        return nil, err
    }
    return
}
func ReadShadowData(im image.Image) (b []byte, err error) {
    head, err := ReadShadowHeader(im)
    if err != nil {
        return nil, err
    }
    length := int(ReadShadowLength(head))
    var bk []byte = make([]byte, length*8)
    b = make([]byte, length)
    _, err = SetImage(im, func(index, x, y int, in, out image.Image) {
        if index >= 64 && index < length*8+64 {
            R := readRGBAColor(im.At(x, y)).R
            bk[index-64] = uint8(R & 1)
        }
    })
    var bb [8]byte
    var bs []byte
    for i := 0; i < length; i++ {
        bs = bk[8*i : 8*(i+1)]
        for j := 0; j < 8; j++ {
            bb[j] = bs[j]
        }
        b[i] = Bits2Byte(bb)
    }
    return
}
func ReadShadowHeader(im image.Image) (b [8]byte, err error) {
    var bm [64]byte
    _, err = SetImage(im, func(index, x, y int, in, out image.Image) {
        rgba := readRGBAColor(im.At(x, y))
        if index < 64 {
            bm[index] = uint8(rgba.R & 1)
        }
    })
    if err != nil {
        return
    }
    var bb [8]byte
    var bs []byte
    for i := 0; i < 8; i++ {
        bs = bm[8*i : 8*(i+1)]
        for j := 0; j < 8; j++ {
            bb[j] = bs[j]
 &nb