1、图片压缩

+ (UIImage *)compressImage:(UIImage *)image toByte:(NSUInteger)maxLength {
    // Compress by quality
    CGFloat compression = 1;
    NSData *data = UIImageJPEGRepresentation(image, compression);
    if (data.length < maxLength) return image;
    CGFloat max = 1;
    CGFloat min = 0;
    for (int i = 0; i < 6; ++i) {
        compression = (max + min) / 2;
        data = UIImageJPEGRepresentation(image, compression);
        if (data.length < maxLength * 0.9) {
            min = compression;
        }else if (data.length > maxLength) {
            max = compression;
        }else {
            break;
        }
    }
    UIImage *resultImage = [UIImage imageWithData:data];
    if (data.length < maxLength) return resultImage;
    // Compress by size
    NSUInteger lastDataLength = 0;
    while (data.length > maxLength && data.length != lastDataLength) {
        lastDataLength = data.length;
        CGFloat ratio = (CGFloat)maxLength / data.length;
        CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)), (NSUInteger)(resultImage.size.height * sqrtf(ratio))); // Use NSUInteger to prevent white blank
        resultImage = [[self class] scaleImage:resultImage toNewSize:size];
        data = UIImageJPEGRepresentation(resultImage, compression);
    }
     return resultImage;
}

+ (UIImage *)scaleImage:(UIImage *)image toNewSize:(CGSize)size {
    
    UIGraphicsImageRenderer *renderer = [[UIGraphicsImageRenderer alloc]initWithSize:size];
    UIImage *result = [renderer imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
        [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
    }];
    return result;
}

+ (UIImage *)resizeImage:(UIImage *)image maxSize:(CGSize)size {
    CGSize imageSize = image.size;
    CGFloat scale = image.scale;
//    CGFloat screenScale = [UIScreen mainScreen].scale;
    
    float widthScale = 1, heightScale = 1;
    
    if (imageSize.width * scale > size.width) {
        widthScale = (imageSize.width * scale) / (size.width);
    }
    
    if (imageSize.height * scale > size.width) {
        heightScale = (imageSize.height * scale) / (size.width);
    }
    
    float outputScale = MAX(widthScale, heightScale);
    
    if (outputScale > 1) {
        return [self.class scaleImage:image toNewSize:CGSizeApplyAffineTransform(imageSize, CGAffineTransformMakeScale(scale/outputScale, scale/outputScale))];
    } else {
        return image;
    }
}