如何在iOS中将自定义元数据写入PNG图像
如何在iOS中将自定义元数据写入PNG图像
提问于 2013-03-04 22:08:28
我的应用程序应该能够将自定义元数据条目写入PNG图像，以便导出到UIPasteboard。
通过拼凑出关于这个主题的各种帖子，我可以把下面给出的课程作为来源。
通过按钮触发copyPressed方法，我可以使用JPG图像(EXIF)设置自定义元数据：
Image[6101:907] found jpg exif dictionary
Image[6101:907] checking image metadata on clipboard
Image[6101:907] {
ColorModel = RGB;
Depth = 8;
Orientation = 1;
PixelHeight = 224;
PixelWidth = 240;
"{Exif}" = {
ColorSpace = 1;
PixelXDimension = 240;
PixelYDimension = 224;
UserComment = "Here is a comment";
};
"{JFIF}" = {
DensityUnit = 0;
JFIFVersion = (
1,
1
);
XDensity = 1;
YDensity = 1;
};
"{TIFF}" = {
Orientation = 1;
};
}虽然我能够很好地读取PNG元数据，但我似乎无法给它写信：
Image[6116:907] found png property dictionary
Image[6116:907] checking image metadata on clipboard
Image[6116:907] {
ColorModel = RGB;
Depth = 8;
PixelHeight = 224;
PixelWidth = 240;
"{PNG}" = {
InterlaceType = 0;
};
}然而，文档中没有任何东西表明这应该失败，而且许多PNG-特定元数据常量的存在表明它应该成功。
我的应用程序应该使用PNG来避免JPG有损压缩。
为什么我不能在iOS中的内存中PNG映像上设置自定义元数据？
注意:我见过这个问题，但它没有解决这里的问题，即如何具体地将元数据写入PNG图像。
IMViewController.m
#import "IMViewController.h"
#import <ImageIO/ImageIO.h>
@interface IMViewController ()
@end
@implementation IMViewController
- (IBAction)copyPressed:(id)sender
{
// [self copyJPG];
[self copyPNG];
}
-(void)copyPNG
{
NSData *pngData = UIImagePNGRepresentation([UIImage imageNamed:@"wow.png"]);
CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)pngData, NULL);
NSDictionary *metadata = (__bridge NSDictionary *) CGImageSourceCopyPropertiesAtIndex(source, 0, NULL);
NSMutableDictionary *mutableMetadata = [metadata mutableCopy];
NSMutableDictionary *dict = [[mutableMetadata objectForKey:(NSString *) kCGImagePropertyPNGDictionary] mutableCopy];
if (dict) {
NSLog(@"found png property dictionary");
} else {
NSLog(@"creating png property dictionary");
dict = [NSMutableDictionary dictionary];
}
// set values on the root dictionary
[mutableMetadata setObject:@"Name of Software" forKey:(NSString *)kCGImagePropertyPNGDescription];
[mutableMetadata setObject:dict forKey:(NSString *)kCGImagePropertyPNGDictionary];
// set values on the internal dictionary
[dict setObject:@"works" forKey:(NSString *)kCGImagePropertyPNGDescription];
CFStringRef UTI = CGImageSourceGetType(source);
NSMutableData *data = [NSMutableData data];
CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef) data, UTI, 1, NULL);
if (!destination) {
NSLog(@">>> Could not create image destination <<<");
return;
}
CGImageDestinationAddImageFromSource(destination, source, 0, (__bridge CFDictionaryRef) mutableMetadata);
BOOL success = CGImageDestinationFinalize(destination);
if (!success) {
NSLog(@">>> Error Writing Data <<<");
}
UIPasteboard *pasteboard = [UIPasteboard generalPasteboard];
[pasteboard setData:data forPasteboardType:@"public.png"];
[self showPNGMetadata];
}
-(void)copyJPG
{
NSData *jpgData = UIImageJPEGRepresentation([UIImage imageNamed:@"wow.jpg"], 1);
CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef) jpgData, NULL);
NSDictionary *metadata = (__bridge NSDictionary *) CGImageSourceCopyPropertiesAtIndex(source, 0, NULL);
NSMutableDictionary *mutableMetadata = [metadata mutableCopy];
NSMutableDictionary *exif = [[mutableMetadata objectForKey:(NSString *)kCGImagePropertyExifDictionary] mutableCopy];
if (exif) {
NSLog(@"found jpg exif dictionary");
} else {
NSLog(@"creating jpg exif dictionary");
}
// set values on the exif dictionary
[exif setObject:@"Here is a comment" forKey:(NSString *)kCGImagePropertyExifUserComment];
[mutableMetadata setObject:exif forKey:(NSString *)kCGImagePropertyExifDictionary];
CFStringRef UTI = CGImageSourceGetType(source);
NSMutableData *data = [NSMutableData data];
CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef) data, UTI, 1, NULL);
if(!destination) {
NSLog(@">>> Could not create image destination <<<");
return;
}
CGImageDestinationAddImageFromSource(destination,source, 0, (__bridge CFDictionaryRef) mutableMetadata);
BOOL success = CGImageDestinationFinalize(destination);
if (!success) {
NSLog(@">>> Could not create data from image destination <<<");
}
UIPasteboard *pasteboard = [UIPasteboard generalPasteboard];
[pasteboard setData:data forPasteboardType:@"public.jpeg"];
[self showJPGMetadata];
}
-(void)showJPGMetadata
{
NSLog(@"checking image metadata on clipboard");
UIPasteboard *pasteboard = [UIPasteboard generalPasteboard];
NSData *data = [pasteboard dataForPasteboardType:@"public.jpeg"];
CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)data, NULL);
NSDictionary *metadata = (__bridge NSDictionary *) CGImageSourceCopyPropertiesAtIndex(source,0,NULL);
NSLog(@"%@", metadata);
}
-(void)showPNGMetadata
{
NSLog(@"checking image metadata on clipboard");
UIPasteboard *pasteboard = [UIPasteboard generalPasteboard];
NSData *data = [pasteboard dataForPasteboardType:@"public.png"];
CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)data, NULL);
NSDictionary *metadata = (__bridge NSDictionary *) CGImageSourceCopyPropertiesAtIndex(source,0,NULL);
NSLog(@"%@", metadata);
}
@endStack Overflow用户
发布于 2013-03-16 20:34:49
如果您想用修改过的元数据保存映像
[data writeToFile:[NSTemporaryDirectory() stringByAppendingPathComponent:@"test.png"]
atomically:YES];在Finder中查看它的属性。您将看到成功地设置了kCGImagePropertyPNGDescription字段。
但是，如果您尝试读取这个新文件的元数据，kCGImagePropertyPNGDescription将丢失。
ColorModel = RGB;
Depth = 8;
PixelHeight = 1136;
PixelWidth = 640;
"{PNG}" = {
InterlaceType = 0;
};经过一些研究，我发现PNG不包含元数据。但它可能含有XMP元数据。然而，ImageIO似乎没有与XMP一起工作。
也许您可以尝试使用ImageMagic或利比克夫。
有用的链接：
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/15212083
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