一般要做正圆形图片，只能是正方形的基础上才能实现，否则就变成椭圆了，下面说说如何使长方形的图片生成正圆形图片 
废话不多说，没图没真相，先上图吧： 
原图： 


变成正圆后： 


下面上代码： 

    public static Bitmap makeRoundCorner(Bitmap bitmap)    {        int width = bitmap.getWidth();        int height = bitmap.getHeight();        int left = 0, top = 0, right = width, bottom = height;        float roundPx = height/2;        if (width > height) {            left = (width - height)/2;            top = 0;            right = left + height;            bottom = height;        } else if (height > width) {            left = 0;            top = (height - width)/2;            right = width;            bottom = top + width;            roundPx = width/2;        }        ZLog.i(TAG, "ps:"+ left +", "+ top +", "+ right +", "+ bottom);        Bitmap output = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);        Canvas canvas = new Canvas(output);        int color = 0xff424242;        Paint paint = new Paint();        Rect rect = new Rect(left, top, right, bottom);        RectF rectF = new RectF(rect);        paint.setAntiAlias(true);        canvas.drawARGB(0, 0, 0, 0);        paint.setColor(color);        canvas.drawRoundRect(rectF, roundPx, roundPx, paint);        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));        canvas.drawBitmap(bitmap, rect, rect, paint);        return output;    }

下面再解释下： 
由于图片是长方形，所以图片的 宽、高 肯定会有一边要小于另一边，要生成正方形就已最小的一边为基准，再来裁切定位另一边的显示范围 
至于圆角的半径则是正方形宽的一半，用过 CSS 的就知道，画圆很方便 border-radius设为 50% 就可以了，都是一个道理 
android 的 UI 真是太繁琐了 
矩形画个圆角的代码： 

    public static Bitmap makeRoundCorner(Bitmap bitmap, int px)    {        int width = bitmap.getWidth();        int height = bitmap.getHeight();        Bitmap output = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);        Canvas canvas = new Canvas(output);        int color = 0xff424242;        Paint paint = new Paint();        Rect rect = new Rect(0, 0, width, height);        RectF rectF = new RectF(rect);        paint.setAntiAlias(true);        canvas.drawARGB(0, 0, 0, 0);        paint.setColor(color);        canvas.drawRoundRect(rectF, px, px, paint);        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));        canvas.drawBitmap(bitmap, rect, rect, paint);        return output;    }

Android长方形图片生成正圆形，以及矩形图片生成圆角