iOS 图片处理-图片旋转和裁剪

项目中要求处理图片, 简单记录一下图片旋转和裁剪过程

/** 将图片旋转弧度radians */
- (UIImage *)imageRotatedByRadians:(CGFloat)radians
{
    // calculate the size of the rotated view's containing box for our drawing space
    UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,self.size.width, self.size.height)];
    CGAffineTransform t = CGAffineTransformMakeRotation(radians);
    rotatedViewBox.transform = t;
    CGSize rotatedSize = rotatedViewBox.frame.size;
    
    // Create the bitmap context
    UIGraphicsBeginImageContext(rotatedSize);
    CGContextRef bitmap = UIGraphicsGetCurrentContext();
    
    // Move the origin to the middle of the image so we will rotate and scale around the center.
    CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);
    
    //   // Rotate the image context
    CGContextRotateCTM(bitmap, radians);
    
    // Now, draw the rotated/scaled image into the context
    CGContextScaleCTM(bitmap, 1.0, -1.0);
    CGContextDrawImage(bitmap, CGRectMake(-self.size.width / 2, -self.size.height / 2, self.size.width, self.size.height), [self CGImage]);
    
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return newImage;
}

#pragma mark - 截取当前image对象rect区域内的图像
- (UIImage *)subImageWithRect:(CGRect)rect
{
    CGImageRef newImageRef = CGImageCreateWithImageInRect(self.CGImage, rect);
    
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];
    
    CGImageRelease(newImageRef);
    
    return newImage;
}

#pragma mark - 压缩图片至指定尺寸
- (UIImage *)rescaleImageToSize:(CGSize)size
{
    CGRect rect = (CGRect){CGPointZero, size};
    
    UIGraphicsBeginImageContext(rect.size);
    
    [self drawInRect:rect];
    
    UIImage *resImage = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    
    return resImage;
}

#pragma mark - 压缩图片至指定像素
- (UIImage *)rescaleImageToPX:(CGFloat )toPX
{
    CGSize size = self.size;
    
    if(size.width <= toPX && size.height <= toPX)
    {
        return self;
    }
    
    CGFloat scale = size.width / size.height;
    
    if(size.width > size.height)
    {
        size.width = toPX;
        size.height = size.width / scale;
    }
    else
    {
        size.height = toPX;
        size.width = size.height * scale;
    }
    
    return [self rescaleImageToSize:size];
}

一些处理UIImage相关的category: https://github.com/wyon0313/UIImageCategory