Why Does My Byte Array Contain Zeros After Converting a Bitmap Using copyPixelsToBuffer?

Preserving Bitmap Data with Byte Array Conversions

Bitmap manipulation is a common task in Android development, often involving converting bitmaps to byte arrays for data storage or transmission. However, some developers encounter difficulties when attempting to perform this conversion, leading to the following question:

Q: Why is the copied byte array filled with zeros after converting a bitmap using copyPixelsToBuffer?

The provided code snippet demonstrates an attempt to convert a bitmap to a byte array using copyPixelsToBuffer, but the resulting buffer contains only zeroes. To understand the cause of this issue, let's analyze the code:

• The bitmap is obtained from an intent.
• Its size is calculated using the height and row bytes of the bitmap.
• A ByteBuffer is allocated with the calculated size.
• copyPixelsToBuffer is invoked to copy the bitmap pixels into the buffer.
• A byte array of the same size is created.
• The buffer is retrieved into the byte array.

Upon further examination, it becomes evident that the issue lies in the copyPixelsToBuffer method itself. When using an immutable bitmap, it doesn't perform an actual pixel copy but returns a duplicate reference. Thus, any subsequent modifications to the bitmap won't be reflected in the copied buffer.

Solution: Alternative Method for Bitmap Conversion

To effectively convert a bitmap to a byte array, an alternative method must be employed. One reliable approach is to compress the bitmap using a format such as PNG or JPEG and store the compressed data in a byte array. Here's an example:

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

This code snippet follows these steps:

• Compresses the bitmap into a PNG or JPEG format using the ByteArrayOutputStream.
• Obtains the compressed data as a byte array.
• Releases the original bitmap after the conversion is complete.

Remember, bitmap data can also be retrieved from a byte array using the BitmapFactory class:

BitmapFactory.decodeByteArray(byteArray, 0, byteArray.length);

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