在android中创建缩放位图时保持图像质量

Question

I have an image of dimension 960x800 and I am trying to make it fill the screen.

The way I have been currently doing it is by loading the full 960x800 bitmap and using source and destination Rect objects. So far example, my destination rectangle is 480x320 (the dimensions of my screen) and the source rectangle will be 960x800.

background = BitmapFactory.decodeResource(getResources(), R.drawable.background, null);
destRect = new Rect(0,0, screenWidth, screenHeight);
sourceRect = new Rect(0,0, background.getWidth(), background.getHeight());
...
c.drawBitmap(background, sourceRect, destRect, backgroundPaint);

If I then use a Paint object and set dither true when trying the background to the canvas, the image looks absolutely perfect.

Paint backgroundPaint = new Paint();
backgroundPaint .setDither(true);

I have concluded that this may not be very efficient, causing unnecessary work to be done on each draw call. To combat this, I want to try and do the following:

background = BitmapFactory.decodeResource(getResources(), R.drawable.background, null);
background = Bitmap.createScaledBitmap(background, display.getWidth(), display.getHeight(), true);

Thereby creating an already sized bitmap, elminating the need for any Rect objects. However, when doing this I cannot retain the same image quality as I can with the above method. In fact, the image looks similar to that which can be seen if I do not use a Paint object with the aforementioned method. Using the paint object on the scaled bitmap has seemingly no effect.

To give an example of how my image looks, it is similar to this picture (althought not as severe)

Is there something I can do to get the same image quality?

Answer 1

this is the condition if you want your image to be of width 140nyour height will get resized automatically

    Bitmap originalBitmap = BitmapFactory.decodeFile(getResources(), R.drawable.background, null);
    Bitmap bitmap=originalBitmap;
    if (bitmap !=null) {
        int h = bitmap.getHeight();
        int w = bitmap.getWidth();
        h = 140*h/w;
        w = 140;
        bitmap = Bitmap.createScaledBitmap(bitmap, w, h, true);
        setIconImage(bitmap);
    }