如何压缩jpeg图像与可可？

我有一个jpeg图像，我希望能够使用Cocoa/Core Image/Core Graphics逐渐压缩它。例如，我有A.jpg（3MB），我压缩A并获得B.jpg（1MB），压缩B并获得C.jpg（400KB），直到图像不能再被压缩。如何压缩jpeg图像与可可？

我想使用NSBitmapImageRep representationUsingType：属性没有太大的成功。我使用从压缩图像数据创建的图像代表来尝试和进一步压缩，但如果使用与用于创建初始压缩数据相同因子的压缩因子，则这种方法效果不佳。

这里是我一直在争吵与

 
NSString * fileName = @"largeImage.jpg"; 

NSLog(@"== Initializing ==\n"); 

NSData * imageData = [NSData dataWithContentsOfFile:fileName]; 
NSLog(@"imageData length: %d\n", [imageData length]); 

NSImage * image = [[NSImage alloc] initWithData:imageData]; 
NSBitmapImageRep * bitmapRep = [[image representations] objectAtIndex:0]; 

NSData * data = [bitmapRep representationUsingType:NSJPEGFileType properties:nil]; 
NSLog(@"data length: %d\n", [data length]); 

NSDictionary * dict = [NSDictionary dictionaryWithObject: [NSNumber numberWithFloat:0.5] forKey:NSImageCompressionFactor]; 
NSData * data5 = [bitmapRep representationUsingType:NSJPEGFileType properties:dict]; 
NSLog(@"data5 length: %d\n", [data5 length]); 

NSLog(@"== End ==\n\n"); 

NSLog(@"== Image from Data5 ==\n"); 
NSImage * imageFromData5 = [[NSImage alloc] initWithData:data5]; 
NSBitmapImageRep * bitmapRepFromData5 = [[imageFromData5 representations] objectAtIndex:0]; 

NSData * dataFromImageFromData5 = [bitmapRepFromData5 representationUsingType:NSJPEGFileType properties:nil]; 
NSLog(@"dataFromImageFromData5 length: %d\n", [dataFromImageFromData5 length]); 

dict = [NSDictionary dictionaryWithObject: [NSNumber numberWithFloat:0.5] forKey:NSImageCompressionFactor]; 
NSData * dataFiveFromImageWithData5 = [bitmapRepFromData5 representationUsingType:NSJPEGFileType properties:dict]; 
NSLog(@"dataFiveFromImageWithData5 length: %d\n", [dataFiveFromImageWithData5 length]); 
NSLog(@"== End ==\n\n");

代码这是我的结果

 
> == Initializing == 
> imageData length: 1882694 
> data length: 1888365 
> data5 length: 1102461 
> == End == 

> == Image from Data5 == 
> dataFromImageFromData5 length: 1646137 
> dataFiveFromImageWithData5 length: 1102115 
> == End == 


Try a different image 
> == Initializing == 
> imageData length: 3620257 
> data length: 2889458 
> data5 length: 1404750 
> == End == 

> == Image from Data5 == 
> dataFromImageFromData5 length: 2007951 
> dataFiveFromImageWithData5 length: 1405398 
> == End ==

来源

2009-11-20 phi

你需要每一次降低的因素。重新压缩尚未编辑的JPEG图像，使用相同的质量水平实际上不会改变结果，这应该解释为什么您看不到任何尺寸缩小。

（如果您想确保质量不会降低得超过必要，可以使用递减因子反复重印原始图像，而不是像您的示例中那样链接它们。）

来源

2009-11-20 21:58:39 Rhult

如何压缩jpeg图像与可可？

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