iOS 이미지 압축 크기 제한

1. 두 가지 이미지 압축 방법

NSData *data = UIImageJPEGRepresentation(image, compression);
UIImage *resultImage = [UIImage imageWithData:data];

UIGraphicsBeginImageContext(size);
[image drawInRect:CGRectMake(0, 0, size.width, size.height)];
resultImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

2. 그림을 압축하여 그림 파일을 지정한 크기보다 작게 한다

 ， ， ； ， 。

- (NSData *)compressQualityWithMaxLength:(NSInteger)maxLength {// ， ， 。
    CGFloat compression = 1;
    NSData *data = UIImageJPEGRepresentation(self, compression);
    while (data.length > maxLength && compression > 0) {
        compression -= 0.02;
        data = UIImageJPEGRepresentation(self, compression); // When compression less than a value, this code dose not work
    }
    return data;
}//

- (NSData *)compressQualityWithMaxLength:(NSInteger)maxLength {// 。
   CGFloat compression = 1;
    NSData *data = UIImageJPEGRepresentation(self, compression);
    if (data.length < maxLength) return data;
    CGFloat max = 1;
    CGFloat min = 0;
    for (int i = 0; i < 6; ++i) {
        compression = (max + min) / 2;
        data = UIImageJPEGRepresentation(self, compression);
        if (data.length < maxLength * 0.9) {
            min = compression;
        } else if (data.length > maxLength) {
            max = compression;
        } else {
            break;
        }
    }
    return data;
}

 ， ( )。

-(NSData *)compressBySizeWithMaxLength:(NSUInteger)maxLength{
    UIImage *resultImage = self;
    NSData *data = UIImageJPEGRepresentation(resultImage, 1);
    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
        UIGraphicsBeginImageContext(size);
        // Use image to draw (drawInRect:), image is larger but more compression time
        // Use result image to draw, image is smaller but less compression time
        [resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];
        resultImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        data = UIImageJPEGRepresentation(resultImage, 1);
    }
    return data;
}