有没有一种方法可以对生成的GIF进行无损压缩? [英] Is there a way to do lossless compression for generated GIFs?

问题描述

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?

We are using the following code to generate GIF file from a set of JPEG images, for the setting on doing lossless compression, it doesn't seem to generate a smaller sized file at all. Are we doing the right thing here?

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);

推荐答案

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.

The GIF image format IS lossless compression. However you are compressing a (lossy) compressed format. File size may go up.

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