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，字节全部为 0...从相机返回的位图是不可变的...但这应该不重要，因为它正在执行复制。

这段代码可能有什么问题？

Answer 1

尝试这样的事情：

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

Answer 2

CompressFormat 太慢...

尝试 ByteBuffer。

※※※位图转字节数组※※※

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

// Somehow save (and later load) these as well:
int width = bitmap.getWidth();
int height = bitmap.getHeight();
String format = bitmap.getConfig().name();

※※※字节数组转位图※※※

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

Answer 3

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 4

也许您需要倒带缓冲区？

此外，如果位图的步长（以字节为单位）大于行长度（以像素 * 字节/像素为单位），则可能会发生这种情况。将字节长度设置为 b.remaining() 而不是 size。

Answer 5

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 6

你的字节数组太小了。每个像素占用 4 个字节，而不仅仅是 1 个字节，因此将您的大小乘以 4，以便数组足够大。

Answer 7

Ted Hopp 是正确的，来自 API 文档：

public void copyPixelsToBuffer (Buffer dst)

“...此方法返回后，缓冲区的当前位置会更新：位置会根据写入缓冲区中的元素数量递增。
”

和

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

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

Answer 8

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各个部分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 9

我想这会做 -

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

Answer 10

尝试将字符串-位图或位图-字符串转换

/**
 * @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;
    }
}