iPhone保存的png在我加载回来后不一样了

Posted 2023-03-07

【中文标题】iPhone保存的png在我加载回来后不一样了

【英文标题】：iPhone saved png is different after I load it back

【发布时间】：2012-11-19 14:59:36

【问题描述】：

我想修改 .png 图像并将其保存到文件夹中。

将 uiimage 转换为 NSData 修改一些像素 从修改后的 NSData 创建一个新的 UIImage 将此 UIImage 保存到文件夹中 将此相同的 UIImage 设置为 ImageView 的图像属性

如果我检查UIImage的图像，像素数据是正确的，但如果我加载保存的图像，像素数据与修改后的值有点不同。

例如：

107 -76 -43 -1 //RGBA888格式原始图像的一个像素 93 -89 -56 -1 // 修改后的像素值 93 -89 -56 -1 //像素值，我把它设置为imageView的图像后读回来 95 -91 -57 -1 //我从stroage加载回来后的像素值

我的图片保存方法：

- (void) saveImage: (UIImage*) image toFolder: (NSString*) folder

[self.library saveImage: image toAlbum: folder withCompletionBlock:^(NSError *error) 
    if (error!=nil) 
        NSLog(@"Error: %@", [error description]);

        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error"
                                                        message: [error description]
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
        [alert show];
    else
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Image saved!"
                                                        message: nil
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
        [alert show];
    
];

像素修改方法：

CGImageRef cRef = CGImageRetain(_imageView.image.CGImage);
NSData* pixelData = (NSData*) CFBridgingRelease(CGDataProviderCopyData(CGImageGetDataProvider(cRef)));
// image raw data    
signed char* pixelBytes = (signed char *)[pixelData bytes];

// MODIFY SOME PIXEL HERE

NSData* newPixelData = [NSData dataWithBytes:pixelBytes length:[pixelData length]];
// cast NSData as CFDataRef
CFDataRef imgData = (CFDataRef)CFBridgingRetain(newPixelData);
// Make a data provider from CFData
CGDataProviderRef imgDataProvider = CGDataProviderCreateWithCFData(imgData);

// get PNG properties from cRef
size_t width = CGImageGetWidth(cRef);
size_t height = CGImageGetHeight(cRef);
size_t bitsPerComponent = CGImageGetBitsPerComponent(cRef);
size_t bitsPerPixel = CGImageGetBitsPerPixel(cRef);
size_t bytesPerRow = CGImageGetBytesPerRow(cRef);
CGColorSpaceRef colorSpace = CGImageGetColorSpace(cRef);
CGBitmapInfo info = CGImageGetBitmapInfo(cRef);
CGFloat *decode = NULL;
BOOL shouldInteroplate = NO;
CGColorRenderingIntent intent = CGImageGetRenderingIntent(cRef);

// cRef PNG properties + imgDataProvider's data
CGImageRef throughCGImage = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpace, info, imgDataProvider, decode, shouldInteroplate, intent);
CGDataProviderRelease(imgDataProvider);
// make UIImage with CGImage
UIImage* newImage = [UIImage imageWithCGImage:throughCGImage];
CGImageRelease(throughCGImage);

[self saveImage:newImage toFolder:@"DEMOFOLDER"];

_imageView.image = newImage;

【参考方案1】：

我的错，ios默认将图像保存为JPG。