iOS 圖片局部模糊處理：裁剪區域 -> 模糊 -> 合成回原圖的完整方案

需對 UIImageView 中指定區域（圓形/矩形）進行模糊，核心思路：裁剪目標區域 -> 應用模糊濾鏡 -> 合成回原圖對應位置。觸摸移動時實時更新。

核心步驟與關鍵方法

1. 裁剪區域圖片：

   - (UIImage *)cropImage:(UIImage *)image toRect:(CGRect)rect {
       CGImageRef imageRef = CGImageCreateWithImageInRect(image.CGImage, rect);
       UIImage *cropped = [UIImage imageWithCGImage:imageRef];
       CGImageRelease(imageRef);
       return cropped;
   }
   

2. 高斯模糊（Category 擴展）：

   // UIImage+ImageBlur.m
   - (UIImage *)imageWithGaussianBlur9 {
       float weight[5] = {0.127, 0.195, 0.122, 0.054, 0.016};
       UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
       [self drawInRect:CGRectMake(0,0,self.size.width,self.size.height) blendMode:kCGBlendModeNormal alpha:weight[0]];
       for (int x=1; x<5; x++) {
           [self drawInRect:CGRectMake(x,0,self.size.width,self.size.height) blendMode:kCGBlendModeNormal alpha:weight[x]];
           [self drawInRect:CGRectMake(-x,0,self.size.width,self.size.height) blendMode:kCGBlendModeNormal alpha:weight[x]];
       }
       UIImage *hBlur = UIGraphicsGetImageFromCurrentImageContext();
       UIGraphicsEndImageContext();
       // 垂直同理...
       return vBlur;
   }
   

3. 圓角處理（可選）：

   - (UIImage *)roundedRectImage:(UIImage *)image radius:(CGFloat)r { ... }
   

4. 合成回原圖：

   - (UIImage *)mergeImage:(UIImage *)base withImage:(UIImage *)overlay atRect:(CGRect)rect {
       UIGraphicsBeginImageContextWithOptions(base.size, NO, base.scale);
       [base drawAtPoint:CGPointZero];
       [overlay drawInRect:rect];
       UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
       UIGraphicsEndImageContext();
       return result;
   }
   

5. 觸摸移動實時更新：

   - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
       UITouch *touch = [touches anyObject];
       CGPoint pt = [touch locationInView:imageView];
       // 轉換座標到圖片空間，計算裁剪矩形
       CGRect cropRect = ...;
       UIImage *cropped = [self cropImage:imageView.image toRect:cropRect];
       UIImage *blurred = [cropped imageWithGaussianBlur9];
       UIImage *rounded = [self roundedRectImage:blurred radius:4];
       imageView.image = [self mergeImage:imageView.image withImage:rounded atRect:cropRect];
   }
   

性能提示

• 模糊運算較重，建議降低處理圖片尺寸或使用 CIFilter (Core Image) 硬件加速。
• 實時拖拽時可節流（如 30ms 一幀）避免卡頓。

組合繪圖上下文操作，實現精準局部模糊效果。