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; }