How to get a Bitmap from a raw image
I am reading a raw image from the network. This image has been read by an image sensor, not from a file.
These are the things I know about the image:
~ Height & Width ~ Total size (in bytes) ~ 8-bit grayscale ~ 1 byte/pixelI'm trying to convert this image to a bitmap to display in an imageview.
Here's what I tried:
BitmapFactory.Options opt = new BitmapFactory.Options();
opt.outHeight = shortHeight; //360
opt.outWidth = shortWidth;//248
imageBitmap = BitmapFactory.decodeByteArray(imageArray, 0, imageSize, opt);
decodeByteArray returns null, since it cannot decode my image.
I also tried reading it directly from the input stream, without converting it to a Byte Array first:
imageBitmap = BitmapFactory.decodeStream(imageInputStream, null, opt);
This returns null as well.
I've searched on this & other forums, but cannot find a way to achieve this.
Any ideas?
EDIT: I should add 开发者_JAVA百科that the first thing I did was to check if the stream actually contains the raw image. I did this using other applications `(iPhone/Windows MFC) & they are able to read it and display the image correctly. I just need to figure out a way to do this in Java/Android.
Android does not support grayscale bitmaps. So first thing, you have to extend every byte to a 32-bit ARGB int. Alpha is 0xff, and R, G and B bytes are copies of the source image's byte pixel value. Then create the bitmap on top of that array.
Also (see comments), it seems that the device thinks that 0 is white, 1 is black - we have to invert the source bits.
So, let's assume that the source image is in the byte array called Src. Here's the code:
byte [] src; //Comes from somewhere...
byte [] bits = new byte[src.length*4]; //That's where the RGBA array goes.
int i;
for(i=0;i<src.length;i++)
{
bits[i*4] =
bits[i*4+1] =
bits[i*4+2] = ~src[i]; //Invert the source bits
bits[i*4+3] = 0xff; // the alpha.
}
//Now put these nice RGBA pixels into a Bitmap object
Bitmap bm = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
bm.copyPixelsFromBuffer(ByteBuffer.wrap(bits));
Once I did something like this to decode the byte stream obtained from camera preview callback:
Bitmap.createBitmap(imageBytes, previewWidth, previewHeight,
Bitmap.Config.ARGB_8888);
Give it a try.
for(i=0;i<src.length;i++)
{
bits[i*4] = bits[i*4+1] = bits[i*4+2] = ~src[i]; //Invert the source bits
bits[i*4+3] = 0xff; // the alpha.
}
The conversion loop can take a lot of time to convert the 8 bit image to RGBA, a 640x800 image can take more than 500ms... A quicker solution is to use ALPHA8 format for the bitmap and use a color filter:
//setup color filter to inverse alpha, in my case it was needed
float[] mx = new float[]{
1.0f, 0, 0, 0, 0, //red
0, 1.0f, 0, 0, 0, //green
0, 0, 1.0f, 0, 0, //blue
0, 0, 0, -1.0f, 255 //alpha
};
ColorMatrixColorFilter cf = new ColorMatrixColorFilter(mx);
imageView.setColorFilter(cf);
// after set only the alpha channel of the image, it should be a lot faster without the conversion step
Bitmap bm = Bitmap.createBitmap(width, height, Bitmap.Config.ALPHA_8);
bm.copyPixelsFromBuffer(ByteBuffer.wrap(src)); //src is not modified, it's just an 8bit grayscale array
imageview.setImageBitmap(bm);
Use Drawable create from stream. Here's how to do it with an HttpResponse, but you can get the inputstream anyway you want.
InputStream stream = response.getEntity().getContent();
Drawable drawable = Drawable.createFromStream(stream, "Get Full Image Task");
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