ios - 有没有一种方法可以对生成的GIF进行无损压缩？

Question

我们正在使用以下代码从一组JPEG图像生成GIF文件，对于进行无损压缩的设置，它似乎根本不会生成较小的文件。我们在这里做正确的事吗？

CGImageDestinationRef imageDestination = CGImageDestinationCreateWithURL((CFURLRef)pathUrl, CFSTR("com.compuserve.gif"), images.count, NULL);

// image/frame level properties
NSDictionary *imageProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                 [NSNumber numberWithFloat:delayTime], (NSString *)kCGImagePropertyGIFDelayTime,
                                 nil];
NSDictionary *properties = [NSDictionary dictionaryWithObjectsAndKeys:
                            imageProperties, (NSString *)kCGImagePropertyGIFDictionary, 
                            nil];

for (UIImage *image in [images objectEnumerator]) {
    CGImageDestinationAddImage(imageDestination, image.CGImage, (CFDictionaryRef)properties);
}

// gif level properties
NSDictionary *gifProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                               [NSNumber numberWithInt:0], (NSString *)kCGImagePropertyGIFLoopCount,
                               [NSNumber numberWithInt:1.0], kCGImageDestinationLossyCompressionQuality,
                               nil];
properties = [NSDictionary dictionaryWithObjectsAndKeys:
              gifProperties, (NSString *)kCGImagePropertyGIFDictionary,
              nil];
CGImageDestinationSetProperties(imageDestination, (CFDictionaryRef)properties);
CGImageDestinationFinalize(imageDestination);
CFRelease(imageDestination);

Answer 1

GIF图像格式是无损压缩。但是，您正在压缩(有损)压缩格式。文件大小可能会增加。