Android实现BMP和PNG转换为JPEG格式

项目需求，需要把BMP24位的图片转换成jpeg的格式，在网上查询了一些不同格式图片的基本知识，加以总结，实现了一个简单的Demo程序，先贴代码，然后再进行理解
picSwitcher.java文件：

package com.example.bmptojpeg;import java.io.DataInputStream;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.File;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.ImageFormat;import android.graphics.Rect;import android.graphics.YuvImage;import android.util.Log;public class picSwitcher {    //picture type    public static int BMP_TYPE = 100;    public static int JPEG_TYPE = 101;    public static int PNG_TYPE = 102;    public static int UNKNOW = 104;    //BMP type    public static int BMP_DEEP_1 = 200;    public static int BMP_DEEP_4 = 201;    public static int BMP_DEEP_8 = 202;    public static int BMP_DEEP_16 = 203;    public static int BMP_DEEP_24 = 204;    public static int BMP_DEEP_32 = 205;    public static String TAG = "picSwitcher";    private int[] picInfo;    public static int mFileType;    private String mPath;    public picSwitcher(String path){        mPath = path;    }    public void init(){        if(isBmpFile(mPath)){            mFileType = BMP_TYPE;            picInfo = getBmpInfo(mPath);            Log.i(TAG, "width = " + picInfo[0] + " height = " + picInfo[1]);        }else if(isJpegFile(mPath)){            mFileType = JPEG_TYPE;        }else if(isPngFile(mPath)){            picInfo = getPngInfo(mPath);            Log.i(TAG, "width = " + picInfo[0] + " height = " + picInfo[1]);            mFileType = PNG_TYPE;        }else{            mFileType = UNKNOW;        }        Log.i(TAG, "type = " + mFileType);    }    public int getBmpType(String path){        int type = UNKNOW;        try {            FileInputStream fis = new FileInputStream(path);            DataInputStream dis = new DataInputStream(fis);            int bflen = 2;            byte bf[] = new byte[bflen];            dis.skipBytes(28);            dis.read(bf, 0, bflen);            dis.close();            fis.close();            int deepFlag = byteToInt(bf);            switch (deepFlag) {            case 1:                type = BMP_DEEP_1;                break;            case 4:                type = BMP_DEEP_4;                break;            case 8:                type = BMP_DEEP_8;                break;            case 16:                type = BMP_DEEP_16;                break;            case 24:                type = BMP_DEEP_24;                break;            case 32:                type = BMP_DEEP_32;                break;            default:                type = UNKNOW;                break;            }        } catch (Exception e) {        }        return type;    }    public boolean isPngFile(String path){        boolean reasult = true;        try {            FileInputStream fis = new FileInputStream(path);            DataInputStream dis = new DataInputStream(fis);            int flag = dis.readInt();            dis.close();            fis.close();            Log.i(TAG, "flag = " + flag);            if(flag != 0x89504E47){                reasult = false;            }        } catch (Exception e) {            reasult = false;        }        return reasult;    }    //根据前两个字节来判断‘FFD8’    public boolean isJpegFile(String path){        boolean reasult = true;        try {            FileInputStream fis = new FileInputStream(path);            DataInputStream dis = new DataInputStream(fis);            int bflen = 2;            byte bf[] = new byte[bflen];            dis.read(bf, 0, bflen);            dis.close();            fis.close();            if(byteToInt(bf) != 0xD8FF){                reasult = false;            }        } catch (Exception e) {            reasult = false;            Log.i(TAG, "Exception: " + e);        }        return reasult;    }    //根据前两个字节来判断 BMP为‘BM’    private boolean isBmpFile(String path){        boolean reasult = true;        try {            FileInputStream fis = new FileInputStream(path);            DataInputStream dis = new DataInputStream(fis);            int bflen = 2;            byte bf[] = new byte[bflen];            dis.read(bf, 0, bflen);            dis.close();            fis.close();            if(byteToInt(bf) != 0x4D42){                reasult =  false;            }            dis.close();            fis.close();        } catch (Exception e) {            reasult = false;            Log.i(TAG, "Exception: " + e);        }        return reasult;    }    //18-21位表示width,22-25位表示height    private int[] getBmpInfo(String path){        try {            FileInputStream fis = new FileInputStream(path);            DataInputStream dis = new DataInputStream(fis);            int bflen = 8;            dis.skipBytes(18);            byte bf[] = new byte[bflen];            dis.read(bf, 0, bflen);            dis.close();            fis.close();            return byteToInt2(bf);        }catch (Exception e) {}        return null;    }    //16-19位表示width,20-23位表示height    private int[] getPngInfo(String path){        try {            int []info = new int[2];            FileInputStream fis = new FileInputStream(path);            DataInputStream dis = new DataInputStream(fis);            dis.skipBytes(16);            info[0] = dis.readInt();            info[1] = dis.readInt();            dis.close();            fis.close();            return info;        }catch (Exception e) {}        return null;    }    //bmp 小端序转换成int类型    private int byteToInt(byte [] bt){        int t;        t = bt[0] & 0xFF;          t |= (((int) bt[1] << 8) & 0xFF00);         return t;    }    //bmp 小端序转换成int类型    private int[] byteToInt2(byte [] bt){        int []b = new int[2];        b[0] = bt[0] & 0xFF;          b[0] |= (((int) bt[1] << 8) & 0xFF00);          b[0] |= (((int) bt[2] << 16) & 0xFF0000);          b[0] |= (((int) bt[3] << 24) & 0xFF000000);          b[1] = bt[4] & 0xFF;          b[1] |= (((int) bt[5] << 8) & 0xFF00);          b[1] |= (((int) bt[6] << 16) & 0xFF0000);          b[1] |= (((int) bt[7] << 24) & 0xFF000000);         return b;    }    //将数据转换成YUV数据    private byte[] bmpToYuv(String path){        BitmapFactory.Options option = new BitmapFactory.Options();        option.inSampleSize = 1;        Bitmap bm = BitmapFactory.decodeFile(path,option);        int[] argb = new int[picInfo[0] * picInfo[1]];        bm.getPixels(argb, 0, picInfo[0], 0, 0, picInfo[0], picInfo[1]);        byte[] yuv = new byte[picInfo[0] * picInfo[1] * 3 / 2];        encodeYUV420SP(yuv, argb, picInfo[0], picInfo[1]);        bm.recycle();        return yuv;     }    //数据转换算法，通过标准算法将RGB分量变成YUV420类型数据    private  void encodeYUV420SP(byte[] yuv420sp, int[] argb, int width,            int height) {        final int frameSize = width * height;        int yIndex = 0;        int uvIndex = frameSize;        int a, R, G, B, Y, U, V;        int index = 0;        for (int j = 0; j < height; j++) {            for (int i = 0; i < width; i++) {                a = (argb[index] & 0xff000000) >> 24;                R = (argb[index] & 0xff0000) >> 16;                G = (argb[index] & 0xff00) >> 8;                B = (argb[index] & 0xff) >> 0;                // RGB转换成YUV的公式                Y = ((66 * R + 129 * G + 25 * B + 128) >> 8) + 16;                U = ((-38 * R - 74 * G + 112 * B + 128) >> 8) + 128;                V = ((112 * R - 94 * G - 18 * B + 128) >> 8) + 128;                //写数据，每个像素YYYYUV                yuv420sp[yIndex++] = (byte) ((Y < 0) ? 0                        : ((Y > 255) ? 255 : Y));                if (j % 2 == 0 && index % 2 == 0) {                    yuv420sp[uvIndex++] = (byte) ((V < 0) ? 0                            : ((V > 255) ? 255 : V));                    yuv420sp[uvIndex++] = (byte) ((U < 0) ? 0                            : ((U > 255) ? 255 : U));                }                index++;            }        }    }    //将YUV转换成jpeg格式    private boolean yuvToJpeg(byte [] yuv, String dst){        boolean reasult = true;        try{            File jpegFile = new File(dst);            if(jpegFile.exists()){                jpegFile.delete();            }else{                jpegFile.createNewFile();            }            FileOutputStream fos = new FileOutputStream(jpegFile);            Rect rect = new Rect(0, 0, picInfo[0], picInfo[1]);            YuvImage image = new YuvImage(yuv, ImageFormat.NV21, picInfo[0], picInfo[1], null);            image.compressToJpeg(rect, 100, fos);            fos.close();        }catch(Exception e){            reasult = false;            Log.i(TAG, "Exception: " + e);        }        return reasult;    }    //其他格式转换成jpeg    public boolean toJpeg( String dst){        byte[] yuv = bmpToYuv(mPath);        return yuvToJpeg(yuv, dst);    }}

ImageFormat.NV21的YUV分量存储格式如上图，对应encodeYUV420SP的算法

测试部分，比较简单
MainActivity.java文件：

package com.example.bmptojpeg;import android.app.Activity;import android.os.Bundle;import android.util.Log;public class MainActivity extends Activity {    private picSwitcher bs;    private String src = "/data/local/logo.bmp";    private String dst = "/data/local/boot0.jpg";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        bs = new picSwitcher(src);        bs.init();        if(bs.mFileType == bs.BMP_TYPE){            bs.toJpeg(dst);        }else if(bs.mFileType == bs.PNG_TYPE){            bs.toJpeg(dst);        }else if(bs.mFileType == bs.JPEG_TYPE){            Log.i("picSwitcher", "type is jpeg, doNothing");        }    }}

代码的大概流程如下图，不过只做了从BMP转换到JPEG格式的部分（红色部分）

要理解这部分的流程，必须要知道bmp的文件格式：

随意找了一个720P（1920*1080）bmp的文件打开后如下

红色部分代表的是图片的宽和高

重要说一下代码里面用到的部分： 0-1位：bmp格式的图片为‘BM’，可作为改格式的判断根据 18-21位表示图片的宽width 22-25位表示图片的高height
代码里还涉及到png转jpeg的部分，做简单介绍，720P（1920*1080）png的文件打开后如下

红色部分代表的是图片的宽和高

将PNG和BMP的图片宽高数据比较会发现，数据存储的模式不一样，BMP为小端模式存储，而PNG为大端模式存储，所以在读取宽高数据的时候要做相应的转换

剩余知识可以根据代码来理解，参考雷神博客基础篇
http://blog.csdn.net/leixiaohua1020/article/details/50534150

下面简单写下其他格式转换成BMP的思路：

//通过BitmapFactory.decodeFile（path）得到Bitmap数据Bitmap bitmap=BitmapFactory.decodeFile(path);//然后根据以上的BMP头消息来填充public void saveBmp(Bitmap bitmap ,String filename) {        if (bitmap == null)            return;        // 位图大小        int nBmpWidth = bitmap.getWidth();        int nBmpHeight = bitmap.getHeight();        // 图像数据大小        int bufferSize = nBmpHeight * (nBmpWidth * 3 + nBmpWidth % 4);        try {            File file = new File(filename);            Log.w(TAG,"------File : " +filename );            if (!file.exists()) {                Log.w(TAG,"- not exist-----File : " +filename );                file.createNewFile();            }             else{                file.delete();             }            FileOutputStream fileos = new FileOutputStream(filename);            // bmp文件头            int bfType = 0x4d42;            long bfSize = 14 + 40 + bufferSize;            int bfReserved1 = 0;            int bfReserved2 = 0;            long bfOffBits = 14 + 40;            // 保存bmp文件头            writeWord(fileos, bfType);            writeDword(fileos, bfSize);            writeWord(fileos, bfReserved1);            writeWord(fileos, bfReserved2);            writeDword(fileos, bfOffBits);            // bmp信息头            long biSize = 40L;            long biWidth = nBmpWidth;            long biHeight = nBmpHeight;            int biPlanes = 1;            int biBitCount = 24;            long biCompression = 0L;            long biSizeImage = 0L;            long biXpelsPerMeter = 0L;            long biYPelsPerMeter = 0L;            long biClrUsed = 0L;            long biClrImportant = 0L;            // 保存bmp信息头            writeDword(fileos, biSize);            writeLong(fileos, biWidth);            writeLong(fileos, biHeight);            writeWord(fileos, biPlanes);            writeWord(fileos, biBitCount);            writeDword(fileos, biCompression);            writeDword(fileos, biSizeImage);            writeLong(fileos, biXpelsPerMeter);            writeLong(fileos, biYPelsPerMeter);            writeDword(fileos, biClrUsed);            writeDword(fileos, biClrImportant);            // 像素扫描            byte bmpData[] = new byte[bufferSize];            int wWidth = (nBmpWidth * 3 + nBmpWidth % 4);            for (int nCol = 0, nRealCol = nBmpHeight - 1; nCol < nBmpHeight; ++nCol, --nRealCol)                for (int wRow = 0, wByteIdex = 0; wRow < nBmpWidth; wRow++, wByteIdex += 3) {                    int clr = bitmap.getPixel(wRow, nCol);                    bmpData[nRealCol * wWidth + wByteIdex] = (byte) Color.blue(clr);                    bmpData[nRealCol * wWidth + wByteIdex + 1] = (byte) Color.green(clr);                    bmpData[nRealCol * wWidth + wByteIdex + 2] = (byte) Color.red(clr);                }            fileos.write(bmpData);            fileos.flush();            fileos.close();        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }    //其中writeDword等代表按小端序的模式写入对应的数据字节数，给一个简单的例子        public static void writeLong(FileOutputStream stream, long value) throws IOException {        byte[] b = new byte[4];        b[0] = (byte) (value & 0xff);        b[1] = (byte) (value >> 8 & 0xff);        b[2] = (byte) (value >> 16 & 0xff);        b[3] = (byte) (value >> 24 & 0xff);        stream.write(b);    }

以后有空再继续研究，完善！

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