Decode byte array to bitmap that has been compressed in Java

问题

I am compressing a bitmap in the following way

Bitmap bmpSig = getMyBitMap();
int size = bmpSig.getWidth() * bmpSig.getHeight();
ByteArrayOutputStream out = new ByteArrayOutputStream(size);
bmpSig.compress(Bitmap.CompressFormat.JPEG, 100, out);   
byte[] bytSig = out.toByteArray();

I am then trying to display the image in an Android ImageView from the byte array. When I do this I get an image that is completely black image.

ImageView myImg = (ImageView) findViewById(R.id.img_view);
myImg.setImageBitmap(BitmapFactory.decodeByteArray(bytSig, 0, bytSig.length));

I'm assuming it's because I am missing a step before BitmapFactory.decodeByteArray() to reverse the jpeg compression. Or have I misunderstood how the compression works?

回答1:

I didn't realise that the background of my bitmap (from a Canvas object) was transparent. Since this bitmap is just black lines on a white background the black image is due to compressing to JPEG giving the image a black background.

I have changed

bmpSig.compress(Bitmap.CompressFormat.JPEG, 100, out); 

to

bmpSig.compress(Bitmap.CompressFormat.PNG, 100, out); 

And it is working as expected.

来源：https://stackoverflow.com/questions/5243547/decode-byte-array-to-bitmap-that-has-been-compressed-in-java