Access To Raw Data In Argb_8888 Android Bitmap

I am trying to access the raw data of a Bitmap in ARGB_8888 format on Android, using the copyPixelsToBuffer and copyPixelsFromBuffer methods. However, invocation of those calls see

Solution 1:

One way to access data in Bitmap is to use getPixels() method. Below you can find an example I used to get grayscale image from argb data and then back from byte array to Bitmap (of course if you need rgb you reserve 3x bytes and save them all...):

/*Free to use licence by Sami Varjo (but nice if you retain this line)*/public final classBitmapConverter {

    privateBitmapConverter(){};

   /**
    * Get grayscale data from argb image to byte array
    */publicstaticbyte[] ARGB2Gray(Bitmap img)
   {

       int width = img.getWidth();
       int height = img.getHeight();

       int[] pixels = newint[height*width];
       byte grayIm[] = newbyte[height*width];

       img.getPixels(pixels,0,width,0,0,width,height);

       int pixel=0;
       int count=width*height;

       while(count-->0){
           int inVal = pixels[pixel];

           //Get the pixel channel values from int double r = (double)( (inVal & 0x00ff0000)>>16 );
           double g = (double)( (inVal & 0x0000ff00)>>8  );
           double b = (double)(  inVal & 0x000000ff)      ;

           grayIm[pixel++] = (byte)( 0.2989*r + 0.5870*g + 0.1140*b );
       }

       return grayIm;
   }

   /**
    * Create a gray scale bitmap from byte array
    */publicstatic Bitmap gray2ARGB(byte[] data, int width, int height)
   {
       int count = height*width;
       int[] outPix = newint[count];
       int pixel=0;
       while(count-->0){
           int val = data[pixel] & 0xff; //convert byte to unsigned
           outPix[pixel++] = 0xff000000 | val << 16 | val << 8 | val ;
       }

       Bitmap out =  Bitmap.createBitmap(outPix,0,width,width, height, Bitmap.Config.ARGB_8888);
       returnout;
   }

}

Solution 2:

I realize this is very stale and probably won't help you now, but I came across this recently in trying to get copyPixelsFromBuffer to work in my app. (Thank you for asking this question, btw! You saved me tons of time in debugging.) I'm adding this answer in the hopes it helps others like me going forward...

Although I haven't used this yet to ensure that it works, it looks like that, as of API Level 19, we'll finally have a way to specify not to "apply the alpha" (a.k.a. premultiply) within Bitmap. They're adding a setPremultiplied(boolean) method that should help in situations like this going forward by allowing us to specify false.

I hope this helps!

Solution 3:

My guess is that this might have to do with the byte order of the ByteBuffer you are using. ByteBuffer uses big endian by default. Set endianess on the buffer with

buffer.order(ByteOrder.nativeOrder());

See if it helps.

Moreover, copyPixelsFromBuffer/copyPixelsToBuffer does not change the pixel data in any way. They are copied raw.

Solution 4:

This is an old question, but i got to the same issue, and just figured out that the bitmap byte are pre-multiplied, you can set the bitmap (as of API 19) to not pre-multiply the buffer, but in the API they make no guarantee.

From the docs:

public final void setPremultiplied(boolean premultiplied)

Sets whether the bitmap should treat its data as pre-multiplied. Bitmaps are always treated as pre-multiplied by the view system and Canvas for performance reasons. Storing un-pre-multiplied data in a Bitmap (through setPixel, setPixels, or BitmapFactory.Options.inPremultiplied) can lead to incorrect blending if drawn by the framework.

This method will not affect the behaviour of a bitmap without an alpha channel, or if hasAlpha() returns false.

Calling createBitmap or createScaledBitmap with a source Bitmap whose colors are not pre-multiplied may result in a RuntimeException, since those functions require drawing the source, which is not supported for un-pre-multiplied Bitmaps.