将 UIImage 转换为 CIImage
CIImage *ciImage = [UIImage imageNamed:@"test.png"].CIImage；
将 CIImage 转换为 UIImage
UIImage * image = [UIImage imageWithCIImage:ciimage];
图片转成 Base 64 编码
//UIImage图片转成Base64字符串：
UIImage *originImage = [UIImage imageNamed:@"originImage.png"];
NSData *data = UIImageJPEGRepresentation(originImage, 1.0f);
NSString *encodedImageStr = [data base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
//Base64字符串转UIImage图片：
NSData *decodedImageData = [[NSData alloc]
initWithBase64EncodedString:encodedImageStr options:NSDataBase64DecodingIgnoreUnknownCharacters];
UIImage *decodedImage = [UIImage imageWithData:decodedImageData];
