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iOS应用开发中对UIImage进行截取和缩放的方法详解

2020-01-15 14:16:14丽君

  • 缩放到指定大小，也就是指定的size.
  • 等比缩放。

    1.缩放到指定大小

    
- (UIImage*)imageCompressWithSimple:(UIImage*)image scaledToSize:(CGSize)size
{
  UIGraphicsBeginImageContext(size);
  [image drawInRect:CGRectMake(0,0,size.width,size.height)];
  UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return newImage;
}

    2.等比缩放

    （1）通过缩放系数：

    
- (UIImage*)imageCompressWithSimple:(UIImage*)image scale:(float)scale
{
  CGSize size = image.size;
  CGFloat width = size.width;
  CGFloat height = size.height;
  CGFloat scaledWidth = width * scale;
  CGFloat scaledHeight = height * scale;
  UIGraphicsBeginImageContext(size); // this will crop
  [image drawInRect:CGRectMake(0,0,scaledWidth,scaledHeight)];
  UIImage* newImage= UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return newImage;
}

    scale是缩放系数 。

    （2）通过计算得到缩放系数

    
- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize
{

  UIImage *sourceImage = [UIImage imageNamed:@"test.jpg"];
  UIImage *newImage = nil;
  CGSize imageSize = sourceImage.size;
  CGFloat width = imageSize.width;
  CGFloat height = imageSize.height;
  CGFloat targetWidth = targetSize.width;
  CGFloat targetHeight = targetSize.height;
  CGFloat scaleFactor = 0.0;
  CGFloat scaledWidth = targetWidth;
  CGFloat scaledHeight = targetHeight;
  CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

  if (CGSizeEqualToSize(imageSize, targetSize) == NO)
  {
    CGFloat widthFactor = targetWidth / width;
    CGFloat heightFactor = targetHeight / height;
    if (widthFactor > heightFactor)
      scaleFactor = widthFactor; // scale to fit height
    else
      scaleFactor = heightFactor; // scale to fit width

    scaledWidth= width * scaleFactor;
    scaledHeight = height * scaleFactor;
    // center the image
    if (widthFactor > heightFactor)
    {
      thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
    }
    else if (widthFactor < heightFactor)
    {
      thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
    }
  }

  UIGraphicsBeginImageContext(targetSize); // this will crop
  CGRect thumbnailRect = CGRectZero;
  thumbnailRect.origin = thumbnailPoint;
  thumbnailRect.size.width= scaledWidth;
  thumbnailRect.size.height = scaledHeight;
  [sourceImage drawInRect:thumbnailRect];
  newImage = UIGraphicsGetImageFromCurrentImageContext();

  if(newImage == nil)
    NSLog(@"could not scale image");
  //pop the context to get back to the default
  UIGraphicsEndImageContext();

  return newImage;

}
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