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Error in setting custom StorageFolder in UWP app

I am working on a small UWP app that will take pictures and video and save it at a desired location on the PC.
Here is the code base I am using https://github.com/Microsoft/Windows-universal-samples/blob/master/Samples/CameraStarterKit/cs/MainPage.xaml.cs
When I try to initialize StorageFolder class with a desired path, it comes out as null. It only supports to initialize with following paths
var picturesLibrary = await StorageLibrary.GetLibraryAsync(KnownLibraryId.Documents);
var picturesLibrary = await StorageLibrary.GetLibraryAsync(KnownLibraryId.Music);
var picturesLibrary = await StorageLibrary.GetLibraryAsync(KnownLibraryId.Pictures);
var picturesLibrary = await StorageLibrary.GetLibraryAsync(KnownLibraryId.Videos);
Here is my code:
private StorageFolder _captureFolder = null;
_captureFolder = picturesLibrary.SaveFolder ?? ApplicationData.Current.LocalFolder;
var file = await _captureFolder.CreateFileAsync("SmartPhoto.jpg",
CreationCollisionOption.GenerateUniqueName);
var picturesLibrary = await Task.Run(() =>
System.IO.File.Move(file.Path, #"C:\Temp\Pictures\" + file.Name));
Since StorageFolder is not initializing for C:\Temp\Pictures, I tried to move that file from KnownLibraryId.Pictures to C:\Temp\Pictures and that fails too,
System.UnauthorizedAccessException: 'Access to the path
'C:\Temp\Pictures' is denied.'

This is by design, an UWP app can not - by default - access all locations on your hard drive...
It only has a specific set of folders allowed, but you can enable more by using the file picker or adding capabilities.
As mentioned in the docs here : https://learn.microsoft.com/en-us/windows/uwp/files/file-access-permissions
Universal Windows Apps (apps) can access certain file system locations
by default. Apps can also access additional locations through the file
picker, or by declaring capabilities.

Accessing and creating/deleting files in Pictures Library?

I am attempting to create a file in the Pictures Library as documented in Microsofts UWP api.
The Pictures Library typically has the following path.
%USERPROFILE%\Pictures
I have enabled the Pictures library capability in the app manifest.
Like so:
File.WriteAllBytes("%USERPROFILE%/Pictures", fileData);
It returns:
DirectoryNotFoundException: Could not find a part of the path 'C:\Data\Users\DefaultAccount\AppData\Local\DevelopmentFiles\HoloViewerVS.Debug_x86.jtth.jh\%USERPROFILE%\Pictures'
`
When I try using my username hard-coded, like so:
File.WriteAllBytes("jtth.jh/Pictures", fileData);
it returns the same DirectoryNotFound exception:
DirectoryNotFoundException: Could not find a part of the path 'C:\Data\Users\DefaultAccount\AppData\Local\DevelopmentFiles\HoloViewerVS.Debug_x86.jtth.jh\jtth.jh\Pictures'`
So, how do you access the Pictures Library and write files to it? Clearly I must be missing something small here as the path its trying to access the pictures library at seems quite odd here.
I see it says how to 'Get the Pictures library.' using a StorageFolder:
public static StorageFolder PicturesLibrary { get; }
But I'm not sure how to add files to this folder variable like the way I'm doing it using the file write.
Can I do it the way I am trying to do it, or do I need to jump through StorageFolder and/or async hoops?
Example for clarification:
string imgName = currentFolderLoaded + "/" + temp.GetComponentInChildren<Text>().text;
//example imgName to enhance clairty
imgName = C:\dev\Users\jtth\Hololens\ProjectFolder\App\HoloApp\Data\myFiles\pics\example.png
//load image
byte[] fileData;
Texture2D tex = null;
fileData = File.ReadAllBytes(imgName);
tex = new Texture2D(2, 2);
tex.LoadImage(fileData);
//test hololens access
//previous attempt -> File.WriteAllBytes("%USERPROFILE%/Pictures", fileData);
//New attempt
AsStorageFile(fileData, imgName);
//Read Texture into RawImage component
ImgObject.GetComponent<RawImage>().material.mainTexture = tex;
//Enable component to render image in game
ImgObject.GetComponent<RawImage>().enabled = true;
Function:
private static async Task<StorageFile> AsStorageFile(byte[] byteArray, string fileName)
{
Windows.Storage.StorageFolder storageFolder = Windows.Storage.KnownFolders.PicturesLibrary;
Windows.Storage.StorageFile sampleFile = await storageFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);
await Windows.Storage.FileIO.WriteBytesAsync(sampleFile, byteArray);
return sampleFile;
}

I'm checking the Photos app on the Hololens after running through this code and it doesn't seem to be creating the picture?
If you want your pictures showed in the Photos app on Hololens, actually you may need to save the pictures into CameraRoll folder.
But it seems like it cannot be directly saved, you may need to move the picture file as a workaround.
var cameraRollFolder = Windows.Storage.KnownFolders.CameraRoll.Path;
File.Move(_filePath, Path.Combine(cameraRollFolder, _filename));
Details please reference this similar thread.

It is because UWP applications work under isolated storage. Like the first example in your linked MSDN article says, do something like this:
StorageFolder storageFolder = KnownFolders.PicturesLibrary;
StorageFile file = await storageFolder.CreateFileAsync("sample.png", CreationCollisionOption.ReplaceExisting);
// Do something with the new file.
Plain File.Xxx() calls will be isolated to your application's own little world.

c# UWP Save StorageFile Without Dialog

I am in trouble with some issue about FileSavePicker. Is there any solution about saving a StorageFile without showing any popup or dialog to ask user. I want to give the current path of the storage file from code behind.
var byteArray = Convert.FromBase64String(Base64);
StorageFile file = await Windows.Storage.ApplicationData.Current.LocalFolder.CreateFileAsync("file.jpg", CreationCollisionOption.ReplaceExisting);
await Windows.Storage.FileIO.WriteBytesAsync(file, byteArray);
var savePicker = new FileSavePicker();
savePicker.FileTypeChoices.Add("JPEG-Image", new List<string>() { ".jpg" });
savePicker.SuggestedSaveFile = file;
savePicker.PickSaveFileAsync();

...We have to use a few paths which are defined under
'Windows.Storage.KnownFolders'...
it is not so. In fact your app can access any folder on device but it will need additional permissions. The most straightforward way to obtain permission you should do next:
1) ask user to pick folder from FolderPicker
2) store selected folder to StorageApplicationPermissions.FutureAccessList
After this your app can do anything with this folder.
Code that demonstrate how to obtain permissions:
var picker = new FolderPicker();
var pfolder = await picker.PickSingleFolderAsync();
StorageApplicationPermissions.FutureAccessList.Add(pfolder);
Code that demonstrate how to create file in desired folder:
var folder = await StorageFolder.GetFolderFromPathAsync("your path");
var file = await folder.CreateFileAsync("text.txt");
using (var writer = await file.OpenStreamForWriteAsync())
{
await writer.WriteAsync(new byte[100], 0, 0);
}
But keep in mind that "your path" is folder or any of subfolder that was stored to StorageApplicationPermissions.FutureAccessList. More details here FutureAccessList

StorageFile.GetFileFromPathAsync() is probably what you are looking for. I think the file must be created beforehand for this method to work. Be aware that creating the file in some locations might need additional permissions or is even impossible (I don't know how UWP and UAC interact).
Another possibility is to use Win32 APIs inside UWP apps. Maybe this can solve your problem if the desired API is available.

I want to thank you all for your interest. I figured out the solution. If you do not want to use any dialog or prompting you can not use FileSavePicker. Here are the simple codes you need to converting Base64 string to image and save.
var byteArray = Convert.FromBase64String(Base64);
StorageFile file = await Windows.Storage.KnownFolders.SavedPictures.CreateFileAsync(
"file.jpg", CreationCollisionOption.ReplaceExisting);
await Windows.Storage.FileIO.WriteBytesAsync(file, byteArray);
I guess there is no way to give specific path. We have to use a few paths which are defined under Windows.Storage.KnownFolders. If it is not, please give some information about it.

C# Saving Jpeg to specific path local

I'm building an app that needs to take a photo with webcam and save it to the local disk, so far I have this:
async private void CapturePhoto_Click(object sender, RoutedEventArgs e)
{
Windows.Storage.StorageFolder localFolder = Windows.Storage.ApplicationData.Current.LocalFolder;
ImageEncodingProperties imgFormat = ImageEncodingProperties.CreateJpeg();
// create storage file in local app storage
StorageFile file = await localFolder.CreateFileAsync("TestPhoto.jpg", CreationCollisionOption.GenerateUniqueName);
StorageFile localFile = await localFolder.CreateFileAsync("webcamPhotoTest.jpg", CreationCollisionOption.ReplaceExisting);
// take photo
// save to app storage
await captureManager.CapturePhotoToStorageFileAsync(imgFormat, file);
// save to local storage
await captureManager.CapturePhotoToStorageFileAsync(imgFormat, localFile);
// Get photo as a BitmapImage
BitmapImage bmpImage = new BitmapImage(new Uri(file.Path));
// imagePreview is a <Image> object defined in XAML
imagePreview.Source = bmpImage;
}
I am able to save the jpg image both to app storage and local storage but I need to be able to
a) Specify the path to save to
b) do so without requiring user interaction (e.g windows save file prompt)
There are no support for System.Drawing in Windows 8 apps which complicates things. Most answers I've found have either been using System.Drawing features or windows' save file prompt.

You can't really use any location that you want. There is the list of locations that you can access from your app: File access and permissions in Windows Store apps. Some locations require additional declarations in the manifest file of your project.

Delete file in Windows Store app

How to delete Database file created by Sqlite-net in Windows store application. I tried this
StorageFile sampleFile = await ApplicationData.Current.LocalFolder.GetFileAsync(databaseName);
sampleFile.DeleteAsync(StorageDeleteOption.Default);
but neither getting any exception nor file is getting deleted. What am i missing here ?

Try awaiting the DeleteAsync as well
StorageFile sampleFile = await ApplicationData.Current.LocalFolder.GetFileAsync(databaseName);
await sampleFile.DeleteAsync(StorageDeleteOption.Default);