将 Java 位图转换为字节数组

  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[]

当我查看调用 copyPixelsToBuffer之后的缓冲区时，字节都是0... ... 从摄像头返回的位图是不可变的... ... 但是这应该不重要，因为它正在进行复制。

这个代码有什么问题吗？

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小开

也许你需要倒带缓冲器?

同样，如果位图的步幅(以字节为单位)大于行长(以像素*字节/像素为单位)，也可能发生这种情况。使字节的长度为b.remaining()而不是size。

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最佳答案

试试这样做:

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

您的字节数组太小。每个像素占用4个字节，而不是1个字节，所以将你的大小乘以4，这样数组就足够大了。

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压缩格式太慢…

ByteBuffer试试。

※※※位图到字节※※※

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


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

※※※字节到位图※※※

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);
小开

Ted Hopp是正确的，摘自API文档:

public void copyPixelsToBuffer (Buffer dst)
< p > "……该方法返回后，缓冲区的当前位置将被更新:位置将按写入缓冲区的元素数量递增。 " < / p >

而且

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

将字节从当前位置读入指定的字节数组，从指定的偏移量开始，并根据所读的字节数增加位置。

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使用下面的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);
}
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为了避免更大文件的OutOfMemory错误，我建议通过将位图分成几个部分并合并它们部分的字节来解决这个任务。

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();
}
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尝试转换字符串-位图或位图-字符串

/**
* @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;
}
}
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下面是用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
}
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我想这个可以

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

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