我有一个 jpeg 图像,我希望能够使用 Cocoa/Core Image/Core Graphics 增量压缩它。例如,我有A.jpg(3MB),我压缩A并得到B.jpg(1MB),压缩B并得到C.jpg(400KB),依此类推,直到图像无法再压缩为止。
我尝试使用 NSBitmapImageReprepresentationUsingType:properties 但没有取得太大成功。我使用从压缩图像数据创建的图像代表来尝试进一步压缩,但如果我使用与创建初始压缩数据相同的压缩因子,则效果不佳。
这是我一直在争论的代码
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");
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 ==
最佳答案
每次都需要减小系数。使用相同的质量级别重新压缩未经编辑的 JPEG 图像实际上根本不会改变结果太多,这应该可以解释为什么您没有看到尺寸有任何减小。
(如果您想确保质量不会降低超过必要的程度,则可以使用递减的因子一遍又一遍地重新压缩原始图像,而不是像示例中那样链接它们。)
关于cocoa - 如何用Cocoa压缩jpeg图像?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1773360/