如何更改位圖的不透明度？

Question

我有一個位圖：

Bitmap bitmap = BitmapFactory.decodeFile("some/arbitrary/path/image.jpg"); 

但我不會顯示圖像給用戶。我希望alpha是100（255）。如果這是不可能的，我可以設置Bitmap的不透明度嗎？

Answer 1

您也可以嘗試BitmapDrawable而不是Bitmap。如果你要看你用位圖的方式，這是非常有用...

編輯

作爲一個評論者問他怎麼可以存儲與阿爾法位圖，下面是一些代碼：

// lets create a new empty bitmap 
Bitmap newBitmap = Bitmap.createBitmap(originalBitmap.getWidth(), originalBitmap.getHeight(), Bitmap.Config.ARGB_8888); 
// create a canvas where we can draw on 
Canvas canvas = new Canvas(newBitmap); 
// create a paint instance with alpha 
Paint alphaPaint = new Paint(); 
alphaPaint.setAlpha(42); 
// now lets draw using alphaPaint instance 
canvas.drawBitmap(originalBitmap, 0, 0, alphaPaint); 

// now lets store the bitmap to a file - the canvas has drawn on the newBitmap, so we can just store that one 
// please add stream handling with try/catch blocks 
FileOutputStream fos = new FileOutputStream(new File("/awesome/path/to/bitmap.png")); 
newBitmap.compress(Bitmap.CompressFormat.PNG, 100, fos); 

Answer 2

據我所知，不透明度或其他顏色過濾器不能在位圖本身設置。您需要在使用圖像時設置Alpha：

如果您使用ImageView，則有ImageView.setAlpha()。

如果您使用的是畫布，那麼你需要使用Paint.setAlpha()：

Paint paint = new Paint(); 
paint.setAlpha(100); 
canvas.drawBitmap(bitmap, src, dst, paint);

此外，結合WarrenFaith的答案，如果你將使用位圖在需要繪製，可以使用BitmapDrawable.setAlpha()。

Answer 3

Bitmap bgr = BitmapFactory.decodeResource(getResources(),R.drawable.main_logo_2);  
Paint transparentpainthack = new Paint(); 
transparentpainthack.setAlpha(100); 
canvas.drawBitmap(bgr, 0, 0, transparentpainthack); 

Answer 4

public Bitmap makeTransparent(Bitmap src, int value) { 
    int width = src.getWidth(); 
    int height = src.getHeight(); 
     Bitmap transBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888); 
     Canvas canvas = new Canvas(transBitmap); 
     canvas.drawARGB(0, 0, 0, 0); 
     // config paint 
     final Paint paint = new Paint(); 
     paint.setAlpha(value); 
     canvas.drawBitmap(src, 0, 0, paint);  
     return transBitmap; 
} 

Answer 5

https://dzone.com/articles/adjusting-opacity-android提出：

/** 
* @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. 
*/ 
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; 
} 

注意與DST_IN可以修改（而不是復位）已經透明圖像的透明度，也就是，你可以使圖像越來越多透明。

Answer 6

如果您使用的是可繪製顯示圖像，您可以按如下改變阿爾法：

private Drawable mTriangle; 
mTriangle = context.getResources().getDrawable(R.drawable.triangle_arrow_for_radar); 

... 

protected void onDraw(Canvas canvas) 
{ 
    // Draw the triangle arrow 
    float imageTargetWidth = getWidth()/15; 
    float scale = mTriangle.getIntrinsicWidth()/imageTargetWidth; 

    int imgWidth = (int)(imageTargetWidth); 
    int imgHeight = (int)(mTriangle.getIntrinsicHeight()/scale); 

    if (mTriangle != null) 
    { 
     mTriangle.setBounds(getWidth()/2 - imgWidth/2, getHeight()/2 -  imgHeight/2, getWidth()/2 + imgWidth/2, getHeight()/2 + imgHeight/2); 

     mTriangle.setAlpha(150); // from (transparent) to 255 (opaque) 
     mTriangle.draw(canvas); 
    } 
}