修剪UIImage白色边框

Question

我无法找到一种方法来裁剪包含白色边框的图像。

目前，它是一个UIImage的，我试图像UIImage+Trim和CKImageAddons一些解决方案，但这些库没有工作。我认为部分问题在于由于图像压缩（我认为），边框不完全是白色的。

有没有人找到解决方案？

感谢，

Answer 1

嗯，我会使用的UIImage +微调，改变它的工作原理来算可见白色像素的方式（因此如果RGB> 255 - small_number_that_still_makes_it_white_but_suffices_to_cut_like_5_to_10）insted的计算不透明的。

后快速浏览一下，计数循环是在这里：

for (NSInteger row = 0; row < height; row++) { 

    for (NSInteger col = 0; col < width; col++) { 

     if (fullyOpaque) { 

      // Found non-transparent pixel 
      if (bitmapData[row*bytesPerRow + col] == UINT8_MAX) { 

       rowSum[row]++; 
       colSum[col]++; 

      } 

     } else { 

      // Found non-transparent pixel 
      if (bitmapData[row*bytesPerRow + col]) { 

       rowSum[row]++; 
       colSum[col]++; 

      } 

     } 

    } 

} 

和切割在后面做，并删除rowSum和colSum是等于0

而且，似乎它创建内部图像一个用于计数：

CGContextRef contextRef = CGBitmapContextCreate(bitmapData, (NSUInteger)width, (NSUInteger)height, 8, (NSUInteger)bytesPerRow, NULL, kCGImageAlphaOnly); 

使用灰度图像，而不是应该工作的简单的方法，它从测试的透明度改变颜色测试。

编辑：好的，解决方案：

- (UIEdgeInsets)transparencyInsetsByCuttingWhitespace:(UInt8)tolerance 
{ 
    // Draw our image on that context 
    NSInteger width = (NSInteger)CGImageGetWidth([self CGImage]); 
    NSInteger height = (NSInteger)CGImageGetHeight([self CGImage]); 
    NSInteger bytesPerRow = width * (NSInteger)sizeof(uint8_t); 

    // Allocate array to hold alpha channel 
    uint8_t * bitmapData = calloc((size_t)(width * height), sizeof(uint8_t)); 

    // Create grayscale image 
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); 
    CGContextRef contextRef = CGBitmapContextCreate(bitmapData, (NSUInteger)width, (NSUInteger)height, 8, (NSUInteger)bytesPerRow, colorSpace, kCGImageAlphaNone); 

    CGImageRef cgImage = self.CGImage; 
    CGRect rect = CGRectMake(0, 0, width, height); 
    CGContextDrawImage(contextRef, rect, cgImage); 

    // Sum all non-transparent pixels in every row and every column 
    uint16_t * rowSum = calloc((size_t)height, sizeof(uint16_t)); 
    uint16_t * colSum = calloc((size_t)width, sizeof(uint16_t)); 

    // Enumerate through all pixels 
    for (NSInteger row = 0; row < height; row++) { 

     for (NSInteger col = 0; col < width; col++) { 

      // Found darker pixel 
      if (bitmapData[row*bytesPerRow + col] <= UINT8_MAX - tolerance) { 

       rowSum[row]++; 
       colSum[col]++; 

      } 
     } 
    } 

    // Initialize crop insets and enumerate cols/rows arrays until we find non-empty columns or row 
    UIEdgeInsets crop = UIEdgeInsetsZero; 

    // Top 
    for (NSInteger i = 0; i < height; i++) { 

     if (rowSum[i] > 0) { 

      crop.top = i; 
      break; 

     } 

    } 

    // Bottom 
    for (NSInteger i = height - 1; i >= 0; i--) { 

     if (rowSum[i] > 0) { 
      crop.bottom = MAX(0, height - i - 1); 
      break; 
     } 

    } 

    // Left 
    for (NSInteger i = 0; i < width; i++) { 

     if (colSum[i] > 0) { 
      crop.left = i; 
      break; 
     } 

    } 

    // Right 
    for (NSInteger i = width - 1; i >= 0; i--) { 

     if (colSum[i] > 0) { 

      crop.right = MAX(0, width - i - 1); 
      break; 

     } 
    } 

    free(bitmapData); 
    free(colSum); 
    free(rowSum); 

    CGContextRelease(contextRef); 

    return crop; 
} 

- (UIImage *)imageByTrimmingWhitePixelsWithOpacity:(UInt8)tolerance 
{ 
    if (self.size.height < 2 || self.size.width < 2) { 

     return self; 

    } 

    CGRect rect = CGRectMake(0, 0, self.size.width * self.scale, self.size.height * self.scale); 
    UIEdgeInsets crop = [self transparencyInsetsByCuttingWhitespace:tolerance]; 

    UIImage *img = self; 

    if (crop.top == 0 && crop.bottom == 0 && crop.left == 0 && crop.right == 0) { 

     // No cropping needed 

    } else { 

     // Calculate new crop bounds 
     rect.origin.x += crop.left; 
     rect.origin.y += crop.top; 
     rect.size.width -= crop.left + crop.right; 
     rect.size.height -= crop.top + crop.bottom; 

     // Crop it 
     CGImageRef newImage = CGImageCreateWithImageInRect([self CGImage], rect); 

     // Convert back to UIImage 
     img = [UIImage imageWithCGImage:newImage scale:self.scale orientation:self.imageOrientation]; 

     CGImageRelease(newImage); 
    } 

    return img; 
}