Why Does My Java Code Fail to Convert a Bitmap to a Byte Array?

Unable to Convert Java Bitmap to Byte Array

The code snippet endeavors to convert a Java bitmap to a byte array for further processing. However, an unexpected error occurs when attempting to copy the bitmap pixels to the buffer. The copied data consistently returns all zeroes. This issue arises despite the bitmap being returned from the camera as immutable.

To understand the underlying problem, consider the following:

  bmp.copyPixelsToBuffer(b);

  byte[] bytes = new byte[size];

  try {
     b.get(bytes, 0, bytes.length);
  } catch (BufferUnderflowException e) {
     // always happens
  }

The copyPixelsToBuffer method copies the pixel data from the bitmap into the provided buffer. However, the buffer size is incorrect, leading to a buffer underflow exception. To resolve this issue, use the size of the buffer returned by b.limit() instead of size:

byte[] bytes = new byte[b.limit()];

Additionally, the conditional logic for handling the buffer underflow exception is not necessary. The exception will occur regardless of the condition, as the buffer is always undersized.

Alternative Approach

Instead of the problematic copyPixelsToBuffer method, consider using an alternative approach to convert the bitmap to a byte array:

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

In this approach, the bitmap is compressed into a PNG-formatted byte array. This method guarantees a valid byte array representation of the bitmap.

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