我有一个UIImage，我希望将它保存到具有DPI元数据集的照片中。我知道UIImage是不可变的，所以我必须创建一个新的UIImage。我使用this answer作为参考，在UIImage上创建一个swift扩展函数，生成一个带有DPI集的新UIImage。我已成功将其保存到UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil)的照片中。我通过电子邮件发送给自己（设置为＆＃39;实际尺寸＆＃39;）并在预览中打开它，但DPI始终保持在72.
这是我转换的函数：
func imageWithDPI(dpi :Int) -> UIImage? {
guard let sourceImageData = UIImageJPEGRepresentation(self, 0.8) else {
print("Couldn't make PNG Respresentation of UIImage")
return nil
}
guard let source = CGImageSourceCreateWithData(sourceImageData, nil) else {
print("Couldn't create source with sourceImageData")
return nil
}
var metadata = CGImageSourceCopyPropertiesAtIndex(source, 0, nil) as? [String:AnyObject] ?? [String:AnyObject]()
metadata[kCGImagePropertyDPIWidth as String] = dpi
metadata[kCGImagePropertyDPIHeight as String] = dpi
var exifDictionary = metadata[kCGImagePropertyTIFFDictionary as String] as? [String:AnyObject] ?? [String:AnyObject]()
exifDictionary[kCGImagePropertyTIFFXResolution as String] = dpi
exifDictionary[kCGImagePropertyTIFFYResolution as String] = dpi
metadata[kCGImagePropertyTIFFDictionary as String] = exifDictionary
var jfifDictionary = metadata[kCGImagePropertyJFIFDictionary as String] as? [String:AnyObject] ?? [String:AnyObject]()
jfifDictionary[kCGImagePropertyJFIFXDensity as String] = dpi
jfifDictionary[kCGImagePropertyJFIFYDensity as String] = dpi
jfifDictionary[kCGImagePropertyJFIFVersion as String] = 1
metadata[kCGImagePropertyJFIFDictionary as String] = jfifDictionary
guard let uti = CGImageSourceGetType(source) else {
print("Couldn't get type from source")
return nil
}
let destinationImageData = NSMutableData()
guard let destination = CGImageDestinationCreateWithData(destinationImageData, uti, 1, nil) else {
print("Couldn't create destination with destinationImageData")
return nil
}
CGImageDestinationAddImageFromSource(destination, source,0, metadata)
CGImageDestinationFinalize(destination)
return UIImage(data: destinationImageData)
}
我在核心图形学方面有点深入，所以任何建议都会非常感激。
非常感谢提前。
答案 0 :(得分：1)
当您从#include <iostream>
#include <string>
int delay;
long long int counter1 = 0; // Add LL beyond 9 digits
long long int endcount = 0; // while loop end counter
long long int seed1 = 0;
int match2 = 0;
int ST = 0;
int flag = 0;
float progress = 0;
int step1 = 0;
int step2 = 0;
int step3 = 0;
int main()
{
system("color b0");
std::cout << "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\n";
std::cout << " Poor Key Finder Version 1.0\n";
std::cout << " Build 01/30/2016\n";
std::cout << "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\n\n";
std::cout << " Enter Starting Key Value\n";
std::cin >> counter1;
std::cout << " Enter Ending Key Value\n";
std::cin >> endcount;
std::cout << " Enter Duplicate Character Counter Value\n";
std::cin >> flag;
system("cls");
std::string str =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()_-+=?<>:\\/~.,;";
std::string str2=
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()_-+=?<>:\\/~.,;";
system("@echo. Started on %date% at %time%>>LogKey.txt");
system("color f0");
std::cout << "Poor Key Finder - Search for " << flag
<< " or more matches \n";
std::cout << "Searching through Key Values of " << counter1 << " thru "<<endcount<<"\n\ n";
std::cout << " WARNING - Program Running Please Wait...\n\n";
while (counter1 <= endcount)
{
seed1 = counter1;
srand(seed1);
random_shuffle(str.begin(), str.end()); // Shuffle the string
ST = 0;
match2 = 0;
progress = ((100 * counter1) / endcount);
if (progress == 25)
{
step1++;
if (step1 == 1)
{
std::cout << "25% Complete\n";
}
else
{
}
}
else if (progress == 50)
{
step2++;
if (step2 == 1)
{
std::cout << "50% Complete\n";
}
else
{
}
}
else if (progress == 75)
{
step3++;
if (step3 == 1)
{
std::cout << "75% Complete\n";
}
else
{
}
}
else if (endcount == counter1)
{
std::cout << "100% Complete\n";
}
else
{
}
while (ST <= 85)
{
if (str[ST] == str2[ST])
{
match2++;
}
else
{
}
ST++;
}
if (match2 >= flag)
{
std::cout << "Greater or Equal to = " << flag << " ===== " << seed1
<< "\n";
}
else
{
}
counter1++;
}
std::cout << "Completed = " << endcount << "\n\n\n";
system("@echo. Ended on %date% at %time%>>LogKey.txt");
system("pause");
return 0;
}
创建时，UIImage可能会剥离图像中的所有元数据，包括DPI。我最近在通过iOS的destinationImageData API共享图片时遇到了这个问题。如果我从UIActivityItemProvider方法返回UIImage *，则所有元数据都会丢失。修复方法是返回- (id)item或NSData *。
尝试直接返回NSURL *，或将其保存到文件＆amp;通过电子邮件发送给自己。
我很想知道为什么要为图像设置DPI？如今，DPI几乎对所有数字图像都毫无意义（除非图像是为了准确地表示物理对象的尺寸）。实际像素分辨率远比DPI重要。