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]
        }
        b[i] = bits2byte(bb)
    }
    return
}
func readshadowflag(b [8]byte) (a [4]byte) {
    for i := 0; i < 4; i++ {
        a[i] = b[i]
    }
    return
}
func readshadowlength(b [8]byte) uint32 {
    var bb [4]byte
    for i := 4; i < 8; i++ {
        bb[i-4] = b[i]
    }
    return bytes2uint32(bb)
}
func openimage(path string) (image.image, error) {
    im_read, err := os.open(path)
    defer im_read.close()
    if err != nil {
        return nil, err
    }
    im, _, err := image.decode(im_read)
    if err != nil {
        return nil, err
    }
    return im, nil
}
//modify image
func setimage(im image.image, f func(index, x, y int, in, out image.image)) (out image.image, err error) {
    if f == nil {
        return im, nil
    }
    index := 0
    bounds := im.bounds()
    out = image.newrgba(bounds)
    var m *image.rgba = out.(*image.rgba)
    for y := bounds.min.y; y < bounds.max.y; y++ {
        for x := bounds.min.x; x < bounds.max.x; x++ {
            m.set(x, y, im.at(x, y))
            f(index, x, y, im, out)
            index += 1
        }
    }
    return out, nil
}
//conert any color to rabga color.
func readrgbacolor(from_color color.color) color.rgba {
    return color.rgbamodel.convert(from_color).(color.rgba)
}
//only write to jpeg formats.
func writeimage(path string, im image.image) error {
    out, err := os.openfile(path, os.o_create, os.modeperm)
    defer out.close()
    if err != nil {
        return err
    }
    err = png.encode(out, im)
    if err != nil {
        return err
    }
    return nil
}
var read_in string
var write_out string
var data string
func init() {
    flag.stringvar(&read_in, "in", "", "image path read in.")
    flag.stringvar(&write_out, "out", "out.jpg", "image path write out.")
    flag.stringvar(&data, "data", "", "data to shadow.")
}
func errhandle(err error) {
    if err != nil {
        log.fatal(err)
    }
}
func main() {
    flag.parse()
    if read_in == "" {
        fmt.println("options:")
        flag.printdefaults()
        return
    }
    im, err := openimage(read_in)
    errhandle(err)
    if data != "" {
        out, err := writeshadow([]byte(data), im)
        errhandle(err)
        err = writeimage(write_out, out)
        errhandle(err)
    } else {
        head, err := readshadowheader(im)
        errhandle(err)
        _flag := readshadowflag(head)
        if _flag != flag {
            fmt.println("image doesn't have shadow data.")
            return
        }
        data, err := readshadowdata(im)
        errhandle(err)
        fmt.println("shadow:", string(data))
    }
}

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