java 将字节数组解码为Java压缩过的位图
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Decode byte array to bitmap that has been compressed in Java
提问by cutts
I am compressing a bitmap in the following way
我正在按以下方式压缩位图
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.
然后我试图从字节数组中在 Android ImageView 中显示图像。当我这样做时，我得到一个完全黑色的图像。
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?
我假设这是因为我在 BitmapFactory.decodeByteArray() 之前缺少一个步骤来反转 jpeg 压缩。还是我误解了压缩的工作原理？
采纳答案by cutts
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.
我没有意识到位图的背景（来自 Canvas 对象）是透明的。由于此位图只是白色背景上的黑色线条，因此黑色图像是由于压缩为 JPEG 使图像具有黑色背景。
I have changed
我改变了
bmpSig.compress(Bitmap.CompressFormat.JPEG, 100, out);
to
到
bmpSig.compress(Bitmap.CompressFormat.PNG, 100, out);
And it is working as expected.
它按预期工作。
