WeiLeiming
3/23/2018 - 1:33 AM

图片缩放

UIImage分类，用于图片缩放 Note: 处理大分辨率图片时，往往容易出现OOM，原因是-[UIImage drawInRect:]在绘制时，先解码图片，再生成原始分辨率大小的bitmap，这是很耗内存的。解决方法是使用更低层的ImageIO接口，避免中间bitmap产生

UIImageSize.m
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- (UIImage *)scaleImage:(UIImage *)image newSize:(CGSize)newSize {
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

+ (UIImage *)scaledImageWithData:(NSData *)data withSize:(CGSize)size scale:(CGFloat)scale orientation:(UIImageOrientation)orientation {
    CGFloat maxPixelSize = MAX(size.width, size.height);
    CGImageSourceRef sourceRef = CGImageSourceCreateWithData((__bridge CFDataRef)data, nil);
    NSDictionary *options = @{(__bridge id)kCGImageSourceCreateThumbnailFromImageAlways: (__bridge id)kCFBooleanTrue,
                              (__bridge id)kCGImageSourceThumbnailMaxPixelSize: [NSNumber numberWithFloat:maxPixelSize]};
    CGImageRef imageRef = CGImageSourceCreateImageAtIndex(sourceRef, 0, (__bridge CFDictionaryRef)options);
    UIImage *resultImage = [UIImage imageWithCGImage:imageRef scale:scale orientation:orientation];
    CGImageRelease(imageRef);
    CFRelease(sourceRef);
    return resultImage;
}