将Java位图转换为字节数组

Question

  Bitmap bmp   = intent.getExtras().get("data");
  int size     = bmp.getRowBytes() * bmp.getHeight();
  ByteBuffer b = ByteBuffer.allocate(size);

  bmp.copyPixelsToBuffer(b);

  byte[] bytes = new byte[size];

  try {
     b.get(bytes, 0, bytes.length);
  } catch (BufferUnderflowException e) {
     // always happens
  }
  // do something with byte[]

当我在调用copyPixelsToBuffer 后查看缓冲区时，字节全为0...从相机返回的位图是不可变的...但这不重要，因为它正在复制。

这段代码有什么问题？

Answer 1

也许你需要倒带缓冲区？

此外，如果位图的步幅（以字节为单位）大于以像素 * 字节/像素为单位的行长度，则可能会发生这种情况。将字节的长度设为 b.remaining() 而不是 size。

Answer 2

试试这样的：

Bitmap bmp = intent.getExtras().get("data");
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bmp.compress(Bitmap.CompressFormat.PNG, 100, stream);
byte[] byteArray = stream.toByteArray();
bmp.recycle();

Answer 3

您的字节数组太小。每个像素占用 4 个字节，而不仅仅是 1，所以将大小乘以 4，这样数组就足够大了。

Answer 4

CompressFormat 太慢了...

试试 ByteBuffer。

※※※位图转字节※※※

width = bitmap.getWidth();
height = bitmap.getHeight();

int size = bitmap.getRowBytes() * bitmap.getHeight();
ByteBuffer byteBuffer = ByteBuffer.allocate(size);
bitmap.copyPixelsToBuffer(byteBuffer);
byteArray = byteBuffer.array();

※※※字节转位图※※※

Bitmap.Config configBmp = Bitmap.Config.valueOf(bitmap.getConfig().name());
Bitmap bitmap_tmp = Bitmap.createBitmap(width, height, configBmp);
ByteBuffer buffer = ByteBuffer.wrap(byteArray);
bitmap_tmp.copyPixelsFromBuffer(buffer);

Answer 5

Ted Hopp 是正确的，来自 API 文档：

public void copyPixelsToBuffer (Buffer dst)

"... 该方法返回后，缓冲区的当前位置被更新：该位置增加了写入缓冲区的元素个数。 "

和

public ByteBuffer get (byte[] dst, int dstOffset, int byteCount)

“从当前位置读取字节到指定的字节数组，从指定的偏移量开始，并将位置增加读取的字节数。”

Answer 6

使用以下函数将位图编码为字节[]，反之亦然

public static String encodeTobase64(Bitmap image) {
    Bitmap immagex = image;
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    immagex.compress(Bitmap.CompressFormat.PNG, 90, baos);
    byte[] b = baos.toByteArray();
    String imageEncoded = Base64.encodeToString(b, Base64.DEFAULT);
    return imageEncoded;
}

public static Bitmap decodeBase64(String input) {
    byte[] decodedByte = Base64.decode(input, 0);
    return BitmapFactory.decodeByteArray(decodedByte, 0, decodedByte.length);
}

Answer 7

为了避免较大文件出现OutOfMemory 错误，我建议通过将位图拆分为多个部分并合并它们的字节来解决该任务。

private byte[] getBitmapBytes(Bitmap bitmap)
{
    int chunkNumbers = 10;
    int bitmapSize = bitmap.getRowBytes() * bitmap.getHeight();
    byte[] imageBytes = new byte[bitmapSize];
    int rows, cols;
    int chunkHeight, chunkWidth;
    rows = cols = (int) Math.sqrt(chunkNumbers);
    chunkHeight = bitmap.getHeight() / rows;
    chunkWidth = bitmap.getWidth() / cols;

    int yCoord = 0;
    int bitmapsSizes = 0;

    for (int x = 0; x < rows; x++)
    {
        int xCoord = 0;
        for (int y = 0; y < cols; y++)
        {
            Bitmap bitmapChunk = Bitmap.createBitmap(bitmap, xCoord, yCoord, chunkWidth, chunkHeight);
            byte[] bitmapArray = getBytesFromBitmapChunk(bitmapChunk);
            System.arraycopy(bitmapArray, 0, imageBytes, bitmapsSizes, bitmapArray.length);
            bitmapsSizes = bitmapsSizes + bitmapArray.length;
            xCoord += chunkWidth;

            bitmapChunk.recycle();
            bitmapChunk = null;
        }
        yCoord += chunkHeight;
    }
    
    return imageBytes;
}


private byte[] getBytesFromBitmapChunk(Bitmap bitmap)
{
    int bitmapSize = bitmap.getRowBytes() * bitmap.getHeight();
    ByteBuffer byteBuffer = ByteBuffer.allocate(bitmapSize);
    bitmap.copyPixelsToBuffer(byteBuffer);
    byteBuffer.rewind();
    return byteBuffer.array();
}

Answer 8

试试这个转换 String-Bitmap 或 Bitmap-String

/**
 * @param bitmap
 * @return converting bitmap and return a string
 */
public static String BitMapToString(Bitmap bitmap){
    ByteArrayOutputStream baos=new ByteArrayOutputStream();
    bitmap.compress(Bitmap.CompressFormat.PNG,100, baos);
    byte [] b=baos.toByteArray();
    String temp=Base64.encodeToString(b, Base64.DEFAULT);
    return temp;
}

/**
 * @param encodedString
 * @return bitmap (from given string)
 */
public static Bitmap StringToBitMap(String encodedString){
    try{
        byte [] encodeByte=Base64.decode(encodedString,Base64.DEFAULT);
        Bitmap bitmap= BitmapFactory.decodeByteArray(encodeByte, 0, encodeByte.length);
        return bitmap;
    }catch(Exception e){
        e.getMessage();
        return null;
    }
}

Answer 9

这是用 Kotlin 编写的位图扩展 .convertToByteArray。

/**
 * Convert bitmap to byte array using ByteBuffer.
 */
fun Bitmap.convertToByteArray(): ByteArray {
    //minimum number of bytes that can be used to store this bitmap's pixels
    val size = this.byteCount

    //allocate new instances which will hold bitmap
    val buffer = ByteBuffer.allocate(size)
    val bytes = ByteArray(size)

    //copy the bitmap's pixels into the specified buffer
    this.copyPixelsToBuffer(buffer)

    //rewinds buffer (buffer position is set to zero and the mark is discarded)
    buffer.rewind()

    //transfer bytes from buffer into the given destination array
    buffer.get(bytes)

    //return bitmap's pixels
    return bytes
}

Answer 10

我认为这样就可以了-

public static byte[] convertBitmapToByteArray(Bitmap bitmap){
        ByteBuffer byteBuffer = ByteBuffer.allocate(bitmap.getByteCount());
        bitmap.copyPixelsToBuffer(byteBuffer);
        byteBuffer.rewind();
        return byteBuffer.array();
    }