How to make bitmap transparent?

问题:

/**
 * @param bitmap
 *            The source bitmap.
 * @param opacity
 *            a value between 0 (completely transparent) and 255 (completely
 *            opaque).
 * @return The opacity-adjusted bitmap. If the source bitmap is mutable it
 *         will be adjusted and returned, otherwise a new bitmap is created.
 *         Source : http://stackoverflow.com/questions/7392062/android-
 *         semitransparent-bitmap-background-is-black/14858913#14858913
 */
private Bitmap adjustOpacity(Bitmap bitmap, int opacity) {
    Bitmap mutableBitmap = bitmap.isMutable() ? bitmap : bitmap.copy(Bitmap.Config.ARGB_8888, true);
    Canvas canvas = new Canvas(mutableBitmap);
    int colour = (opacity & 0xFF) << 24;
    canvas.drawColor(colour, PorterDuff.Mode.DST_IN);
    return mutableBitmap;
}

Using adjustOpacity, I make ImageView's Bitmap be semi-transparent.

Bitmap newBitmap = adjustOpacity(orignalBitmap, 10);
view.setImageBitmap(newBitmap);
view.setBackgroundColor(Color.WHITE);

However, Imageview show more darkent before not white. How do I make a semi-transparent (white background) Imageview with Bitmap?

回答1:

// Convert transparentColor to be transparent in a Bitmap.
public static Bitmap makeTransparent(Bitmap bit, Color transparentColor) {
    int width =  bit.getWidth();
    int height = bit.getHeight();
    Bitmap myBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    int [] allpixels = new int [ myBitmap.getHeight()*myBitmap.getWidth()];
    bit.getPixels(allpixels, 0, myBitmap.getWidth(), 0, 0, myBitmap.getWidth(),myBitmap.getHeight());
    myBitmap.setPixels(allpixels, 0, width, 0, 0, width, height);

    for(int i =0; i<myBitmap.getHeight()*myBitmap.getWidth();i++){
     if( allpixels[i] == transparentColor)

                 allpixels[i] = Color.alpha(Color.TRANSPARENT);
     }

      myBitmap.setPixels(allpixels, 0, myBitmap.getWidth(), 0, 0, myBitmap.getWidth(), myBitmap.getHeight());
      return myBitmap;
}

The above code will take a Bitmap, and return a Bitmap where every pixel which the color is transparentColor is transparent. This works in API as low as level 8, and I have not tested it in any lower.

I typically use something like Color.RED to make my transparent pixels, because I don't use a lot of RED in my assets, but if I do it's a custom red color.

回答2:

Try this. Also note that setAlpha is in 0-255 range

//bmp is your Bitmap object

BitmapDrawable bd = new BitmapDrawable(bmp);
bd.setAlpha(50);

ImageView v = (ImageView) findViewById(R.id.image);
v.setImageDrawable(bd);

回答3:

try this,

newBitmap.setImageResource(android.R.color.transparent);

回答4:

@akaya's answer is the right way except that the constructor is deprecated. The new way since API 4 would be to use:

BitmapDrawable drawable = new BitmapDrawable(getResources(), bitmap);
drawable.setAlpha(100);