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。
通过拼凑关于这个主题的各种帖子,我已经能够提出下面给出的课程作为来源。
使用按钮触发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;
};
}
虽然我能够很好地阅读PNG元数据,但我似乎无法写信给它:
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,文档中没有任何内容表明这应该失败,并且许多PNG-specific metadata constants的存在表明它应该成功。
我的应用应该使用PNG来避免JPG's lossy compression。
为什么我不能在iOS中的内存中PNG图像上设置自定义元数据?
注意:我见过this SO question,但它没有解决这里的问题,这是如何专门为PNG图像写入元数据。
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);
}
@end
答案 0 :(得分:4)
如果您尝试使用修改后的元数据保存图像
[data writeToFile:[NSTemporaryDirectory() stringByAppendingPathComponent:@"test.png"]
atomically:YES];
而不是在Finder中查看它的属性。您将看到kCGImagePropertyPNGDescription
字段已成功设置。
但是,如果您尝试阅读此新文件的元数据,kCGImagePropertyPNGDescription
将会丢失。
ColorModel = RGB;
Depth = 8;
PixelHeight = 1136;
PixelWidth = 640;
"{PNG}" = {
InterlaceType = 0;
};
经过一番研究后,我发现PNG不包含元数据。但它可能包含XMP metadata。但似乎ImageIO
与XMP无关
也许您可以尝试使用ImageMagic或libexif。
有用的链接:
PNG Specification
Reading/Writing image XMP on iPhone / Objective-c
Does PNG support metadata fields like Author, Camera Model, etc?
Does PNG contain EXIF data like JPG?
libexif.sourceforge.net