更改UIImage的NSData大小 – 使用最大兆字节Mb限制压缩和调整UIImage的大小
我有一个用户上传的UIImage。
如果图像数据超过10Mb，我怎么把它调整到最大10Mb？ 到目前为止，我发现的数据大小调整最接近的是：
NSData *imageData = UIImageJPEGRepresentation(theUploadedImage.image, 0.5f);
但是，我似乎没有控制MB的文件大小…只是在第二个参数在JPG表示（图像质量浮动）
必须创build自己的函数来压缩一个尽可能小的图像，如果它仍然超过我的“最大尺寸”，那么它resize，保留并重新开始压缩迭代。 如果超过文件大小，这样做的好处是尽可能接近“最大图像文件大小”。 还包括1024次迭代后的故障安全。 （这应该永远不会超过一分钟（但这是一个永远不会occour的情况下谁使用图像在iPhone上的千兆字节？哈哈））… …
-(void)shrinkImage { //IMPORTANT!!! THIS CODE WAS CREATED WITH "ARC" IN MIND... DO NOT USE WITHOUT ARC UNLESS YOU ALTER THIS CODE TO MANAGE MEMORY float compressionVal = 1.0; float maxVal = 9.7;//MB UIImage *compressedImage = theUploadedImage.image; //get UIImage from imageView int iterations = 0; int totalIterations = 0; float initialCompressionVal = 0.00000000f; while (((((float)(UIImageJPEGRepresentation(compressedImage, compressionVal).length))/(1048576.000000000f)) > maxVal) && (totalIterations < 1024)) { NSLog(@"Image is %f MB", (float)(((float)(UIImageJPEGRepresentation(compressedImage, compressionVal)).length)/(1048576.000000f)));//converts bytes to MB compressionVal = (((compressionVal)+((compressionVal)*((float)(((float)maxVal)/((float)(((float)(UIImageJPEGRepresentation(compressedImage, compressionVal).length))/(1048576.000000000f)))))))/(2)); compressionVal *= 0.97;//subtracts 3% of it's current value just incase above algorithm limits at just above MaxVal and while loop becomes infinite. if (initialCompressionVal == 0.00000000f) { initialCompressionVal = compressionVal; } iterations ++; if ((iterations >= 3) || (compressionVal < 0.1)) { iterations = 0; NSLog(@"%f", compressionVal); compressionVal = 1.0f; compressedImage = [UIImage imageWithData:UIImageJPEGRepresentation(compressedImage, compressionVal)]; float resizeAmount = 1.0f; resizeAmount = (resizeAmount+initialCompressionVal)/(2);//percentage resizeAmount *= 0.97;//3% boost just incase image compression algorithm reaches a limit. resizeAmount = 1/(resizeAmount);//value initialCompressionVal = 0.00000000f; UIView *imageHolder = [[UIView alloc] initWithFrame:CGRectMake(0,0,(int)floorf((float)(compressedImage.size.width/(resizeAmount))), (int)floorf((float)(compressedImage.size.height/(resizeAmount))))];//round down to ensure frame isnt larger than image itself UIImageView *theResizedImage = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,(int)ceilf((float)(compressedImage.size.width/(resizeAmount))), (int)ceilf((float)(compressedImage.size.height/(resizeAmount))))];//round up to ensure image fits theResizedImage.image = compressedImage; [imageHolder addSubview:theResizedImage]; UIGraphicsBeginImageContextWithOptions(CGSizeMake(imageHolder.frame.size.width, imageHolder.frame.size.height), YES, 1.0f); CGContextRef resize_context = UIGraphicsGetCurrentContext(); [imageHolder.layer renderInContext:resize_context]; compressedImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); //after 3 compressions, if we still haven't shrunk down to maxVal size, apply the maximum compression we can, then resize the image (90%?), then re-start the process, this time compressing the compressed version of the image we were checking. NSLog(@"resize"); } totalIterations ++; } if (totalIterations >= 1024) { NSLog(@"Image was too big, gave up on trying to re-size");//too many iterations failsafe. Gave up on trying to resize. } else { NSData *imageData = UIImageJPEGRepresentation(compressedImage, compressionVal); NSLog(@"FINAL Image is %f MB ... iterations: %i", (float)(((float)imageData.length)/(1048576.000000f)), totalIterations);//converts bytes to MB theUploadedImage.image = [UIImage imageWithData:imageData];//save new image to UIImageView. } }