UIImageJPEGRepresentation占用巨大内存

Question

我正试图解决这个问题，但在做了我在操作系统或谷歌上发现的每一件事后都失败了。问题是，当我使用UIImage或UIImagePNGRepresentation将NSData转换为UIImageJPEGRepresentation时，内存大小会增加到30 me (信不信由你)。

这是我的密码

myImage= image;
LoginSinglton*loginObj = [LoginSinglton sharedInstance];
NSError *error;
NSData *pngData = UIImageJPEGRepresentation(image, scaleValue); //scaleVale is 1.
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsPath = [paths objectAtIndex:0]; //Get the docs directory

self.imageCurrentDateAndTime =[self getTimeAndDate];
 self.filePathAndDirectory = [documentsPath stringByAppendingPathComponent:@"Photos Dir"];

NSLog(@"Documents path %@",self.filePathAndDirectory);
if (![[NSFileManager defaultManager] createDirectoryAtPath:self.filePathAndDirectory
                               withIntermediateDirectories:NO
                                                attributes:nil
                                                     error:&error])
{
    NSLog(@"Create directory error: %@", error);
}
self.imageName= [NSString stringWithFormat:@"photo-%@-%@.jpg",loginObj.userWebID,self.imageCurrentDateAndTime];
 NSString *filePath = [self.filePathAndDirectory stringByAppendingPathComponent:self.imageName];

[pngData writeToFile:filePath atomically:YES]; //Write the file
[self writeImageThumbnailToFolder:image];
[self writeImageHomeViewThumbnailToFolder:image];  

我也尝试过以下解决方案-- UIImageJPEGRepresentation - memory release issue

1- Used @autoreleasepool

2- done pngData =0；

但仍然面临着记忆问题。

编辑我想我无法表达我的问题。如果UIImageJPEGRepresentation占用了巨大的内存，就可以了，但是内存应该在保存该映像后恢复到以前的位置。希望这会对你的细节有所帮助。

Answer 1

使用小于1的scaleValue。即使是0.9也会大大减少内存占用，并且质量损失最小。

Answer 2

试试这个：

UIGraphicsBeginImageContext(newSize);
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

如果您的期望得不到解决方案，也不必担心这一点：

UIImage *small = [UIImage imageWithCGImage:original.CGImage scale:0.25 orientation:original.imageOrientation];

在这里获取用于编辑图像或缩放的示例应用程序表单：http://mattgemmell.com/2010/07/05/mgimageutilities/

Answer 3

若要使用最小内存调整大小，请使用CoreGraphics

因此，answer by @Mina，详见完整答案。

#import <ImageIO/ImageIO.h>
-(UIImage*) resizedImageToRect:(CGRect) thumbRect {
    CGImageRef          imageRef = [inImage CGImage];
    CGImageAlphaInfo    alphaInfo = CGImageGetAlphaInfo(imageRef);
    if (alphaInfo == kCGImageAlphaNone)
        alphaInfo = kCGImageAlphaNoneSkipLast;

    // Build a bitmap context that's the size of the thumbRect
    CGContextRef bitmap = CGBitmapContextCreate(
        NULL,
        thumbRect.size.width,       // width
        thumbRect.size.height,      // height
        CGImageGetBitsPerComponent(imageRef),   // really needs to always be 8
        4 * thumbRect.size.width,   // rowbytes
        CGImageGetColorSpace(imageRef),
        alphaInfo
        );

    // Draw into the context, this scales the image
    CGContextDrawImage(bitmap, thumbRect, imageRef);

    // Get an image from the context and a UIImage
    CGImageRef  ref = CGBitmapContextCreateImage(bitmap);
    UIImage*    result = [UIImage imageWithCGImage:ref];

    CGContextRelease(bitmap);   // ok if NULL
    CGImageRelease(ref);

    return result;
}