从CGImageRef创建的UIImage因UIImagePNGRepresentation而失败

4 回答

• 1

  我有同样的问题，但只有在iOS 3.2上测试兼容性时 . 在4.2它工作正常 .

  最后我发现这个http://www.hive05.com/2008/11/crop-an-image-using-the-iphone-sdk/同时适用于两者，虽然有点冗长！

  我将其转换为UIImage上的一个类别：

  UIImage Crop.h

  @interface UIImage (Crop)
  - (UIImage*) imageByCroppingToRect:(CGRect)rect;
  @end
  

  UIImage Crop.m

  @implementation UIImage (Crop)
  
  - (UIImage*) imageByCroppingToRect:(CGRect)rect
  {
      //create a context to do our clipping in
      UIGraphicsBeginImageContext(rect.size);
      CGContextRef currentContext = UIGraphicsGetCurrentContext();
  
      //create a rect with the size we want to crop the image to
      //the X and Y here are zero so we start at the beginning of our
      //newly created context
      CGRect clippedRect = CGRectMake(0, 0, rect.size.width, rect.size.height);
      CGContextClipToRect( currentContext, clippedRect);
  
      //create a rect equivalent to the full size of the image
      //offset the rect by the X and Y we want to start the crop
      //from in order to cut off anything before them
      CGRect drawRect = CGRectMake(rect.origin.x * -1,
                                   rect.origin.y * -1,
                                   self.size.width,
                                   self.size.height);
  
      //draw the image to our clipped context using our offset rect
      CGContextTranslateCTM(currentContext, 0.0, rect.size.height);
      CGContextScaleCTM(currentContext, 1.0, -1.0);
      CGContextDrawImage(currentContext, drawRect, self.CGImage);
  
      //pull the image from our cropped context
      UIImage *cropped = UIGraphicsGetImageFromCurrentImageContext();
  
      //pop the context to get back to the default
      UIGraphicsEndImageContext();
  
      //Note: this is autoreleased
      return cropped;
  }
  
  
  @end
  

  回复于 2024-04-30T07:54:06+08:00
• 1

  在PNG中存在各种块，一些包含调色板信息，一些实际图像数据和一些其他信息，这是一个非常有趣的标准 . IDAT块是实际包含图像数据的位 . 如果没有“IDAT写入文件”，那么libpng在输入数据中创建PNG时遇到了一些问题 .

  我不知道你的stillView.image到底是什么，但是当你传递代码CGImageRef肯定有效时会发生什么？ theRect中的实际值是多少？如果你的theRect超出了图像的范围，那么你试图用来制作UIImage的cgCrop可能很容易为零 - 或者不是nil，但不包含图像或宽度和高度为0的图像，这使得libpng无法工作用 .

  回复于 2024-04-30T07:54:06+08:00
• 3

  看来你正在尝试的灵魂应该有效，但我建议使用这个：

  CGImageRef image = [stillView.image CGImage];
  CGRect cropZone;
  
  size_t cWitdh = cropZone.size.width;
  size_t cHeight = cropZone.size.height;
  size_t bitsPerComponent = CGImageGetBitsPerComponent(image);
  size_t bytesPerRow = CGImageGetBytesPerRow(image) / CGImageGetWidth(image) * cWidth;
  
  //Now we build a Context with those dimensions.
  CGContextRef context = CGBitmapContextCreate(nil, cWitdh, cHeight, bitsPerComponent, bytesPerRow, CGColorSpaceCreateDeviceRGB(), CGImageGetBitmapInfo(image));
  
  CGContextDrawImage(context, cropZone, image);
  
  CGImageRef result  = CGBitmapContextCreateImage(context);
  UIImage * cropUIImage = [[UIImage alloc] initWithCGImage:tmp];
  
  CGContextRelease(context);
  CGImageRelease(mergeResult);
  NSData * imgData = UIImagePNGRepresentation ( cropUIImage);
  

  希望能帮助到你 .

  回复于 2024-04-30T07:54:06+08:00
• 0

  嘿，我在我的应用程序中使用这种类型的逻辑，希望这有助于你......

  UIImage *croppedImage = [self imageByCropping:yourImageView.image toRect:heredefineyourRect];
  
      CGSize size = CGSizeMake(croppedImage.size.height, croppedImage.size.width);
      UIGraphicsBeginImageContext(size);
  
      CGPoint pointImg1 = CGPointMake(0,0);
      [croppedImage drawAtPoint:pointImg1 ];
  
      [[UIImage imageNamed:yourImagenameDefine] drawInRect:CGRectMake(0,532, 150,80) ];//here define your Reactangle
  
      UIImage* result = UIGraphicsGetImageFromCurrentImageContext();
      UIGraphicsEndImageContext();
      croppedImage = result;
      yourCropImageView.image=croppedImage;
      [yourCropImageView.image retain];
  

  希望这能帮助你.... :)

  回复于 2024-04-30T07:54:06+08:00