iOS图片压缩指定比例

/**

• 压缩图片质量，返回值为可直接转化成UIImage对象的NSData对象
• aimLength: 目标大小，单位：字节（b）
• accuracyOfLength: 压缩控制误差范围(+ / -)，本方法虽然给出了误差范围，但实际上很难确定一张图片是否能压缩到误差范围内，无法实现精确压缩。
  */

+ (NSData *)compressImageWithImage:(UIImage *)image aimWidth:(CGFloat)width aimLength:(NSInteger)length accuracyOfLength:(NSInteger)accuracy;

+ (NSData *)compressImageWithImage:(UIImage *)image aimWidth:(CGFloat)width aimLength:(NSInteger)length accuracyOfLength:(NSInteger)accuracy {
     UIImage * newImage = [self imageWithImage:image scaledToSize:CGSizeMake(width, width * image.size.height / image.size.width)];

    NSData  * data = UIImageJPEGRepresentation(newImage, 1);
    NSInteger imageDataLen = [data length];
 
    if (imageDataLen <= length + accuracy) {
        return data;
    } else{
        NSData * imageData = UIImageJPEGRepresentation( newImage, 0.99);
        if (imageData.length < length + accuracy) {
            return imageData;
        }
 
        CGFloat maxQuality = 1.0;
        CGFloat minQuality = 0.0;
        int flag = 0;
 
        while (1) {
            CGFloat midQuality = (maxQuality + minQuality)/2;

            if (flag == 6) {
                NSLog(@"************* %ld ******** %f *************",UIImageJPEGRepresentation(newImage, minQuality).length,minQuality);
                return UIImageJPEGRepresentation(newImage, minQuality);
            }
            flag ++;

            NSData * imageData = UIImageJPEGRepresentation(newImage, midQuality);
            NSInteger len = imageData.length;

            if (len > length+accuracy) {
                NSLog(@"-----%d------%f------%ld-----",flag,midQuality,len);
                maxQuality = midQuality;
                continue;
            }else if (len < length-accuracy){
                 NSLog(@"-----%d------%f------%ld-----",flag,midQuality,len);
                minQuality = midQuality;
                continue;
            }else{
                 NSLog(@"-----%d------%f------%ld--end",flag,midQuality,len);
                return imageData;
                break;
            }
        }
    }
}
  //对图片尺寸进行压缩--
+ (UIImage*)imageWithImage:(UIImage*)image scaledToSize:(CGSize)newSize {
    UIGraphicsBeginImageContext(newSize);
    [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

使用方法
BaseClass是自定义类文件NSobject，128是微信分享小程序所需最大尺寸

[BaseClass compressImageWithImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL  URLWithString:[NSString stringWithFormat:@"%@",@"数据url"]]]] aimWidth:图片宽度 aimLength:128*1024 accuracyOfLength:1024]