AutoScaleImageView.java

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        float scale = getMeasuredWidth() / mMaxImageWidth;
        int width = Math.round(getMeasuredWidth() * scale);
        int height = Math.round(getMeasuredHeight() * scale);

        setMeasuredDimension(width, height);
    }