Develop Reference

How can i convert a file .png to a Bitmap? Nothing works for me. Error "'Failed to decode image. The provided image must be a Bitmap.'" Xamarin.forms

I'm working with Xamarin in the part of Xamarin.Forms i need to convert a file ("image.png") to a Bitmap because when project run its enter in "break mode" and show me this message "Java.Lang.IllegalArgumentException: 'Failed to decode image. The provided image must be a Bitmap.'". So i tried to convert the file in many ways like:
1_ Using methods from System.Drawing.Bitmap but it's show this exception "This operation is not supported in this platform"
2_ Cannot use Android.Graphics because i'm working in xamarin.forms not in xamarin.android.
3_ I tried to convert the "image.png" into a base64 or byte[] array and then into a bitmap but the problem is the same like in first problem because to convert from byte[] array or base64 to a Bitmap i have use methods from System.Drawing.Bitmap.
4_ I tried using the library SkiaSharp but i don't have success because i don't found so much information about how to convert .png to SKBitmap and then convert SKBitmap to Bitmap (even i don't know if this is possible).
5_ Finally i converted "image.png" to a "image.bmp" with an app and use the file .bmp in my project but it doesn't work too.
the "image.png" i have to save in a string variable, well that's the idea.
If you have a solution with SkiaSharp o whatever i will glad
EDIT
here is a part of my code, i just save in a variable the image
Icon = "pin_blue.png";
//i can't use a path because in xamarin you have many size from the same
//image for the different size of the screen
EDIT 2 This is my method to show the pins in google maps
private void ShowPins(List<PointsOfInterest> resultPointsOfInterest)
{
if (resultPointsOfInterest != null && resultPointsOfInterest.Any())
{
var location = Geolocation.GetLastKnownLocationAsync();
PointsOfInterest position = new PointsOfInterest();
if (location != null)
{
position.ccsm0166latitud = location.Result.Latitude;
position.ccsm0166longitud = location.Result.Longitude;
}
else {
position = resultPointsOfInterest.First();
}
//Distance = Distance.FromKilometers(new Random().Next(23,35));
Distance = Distance.FromKilometers(3);
Position = new Position(position.ccsm0166latitud, position.ccsm0166longitud);
PinsFiltered= Pins = new List<PinCustom>(resultPointsOfInterest.Select(
x => new PinCustom()
{
Position =
new Position(x.ccsm0166latitud, x.ccsm0166longitud),
Address = x.ccsm0166direccion,
Label = x.ccsm0166nombre,
Type = PinType.Place,
TypePointOfInterest = x.ccsm0166tipositio,
IconBM = Int32.Parse(x.ccsm0166tipositio) == (int)PointOfInterestType.branch ? PinCustom.ConvertToBitmap("pin_blue.png") :
Int32.Parse(x.ccsm0166tipositio) == (int)PointOfInterestType.branch ? "pin_blue.png" :
Int32.Parse(x.ccsm0166tipositio) == (int)PointOfInterestType.branchWithExtendedHours ? "pin_black.png" :
Int32.Parse(x.ccsm0166tipositio) == (int)PointOfInterestType.branchWithExtendedHours2 ? "pin_black.png" :
Int32.Parse(x.ccsm0166tipositio) == (int)PointOfInterestType.branchWithExtendedHours3 ? "pin_black.png" :
Int32.Parse(x.ccsm0166tipositio) == (int)PointOfInterestType.selfServiceTerminal ? "pin_green.png" :
Int32.Parse(x.ccsm0166tipositio) == (int)PointOfInterestType.atmServBox ? "pin_yellow.png" : string.Empty
}).ToList());
}
else
{
Pins = new List<PinCustom>();
}
}
This is the class Pin where i save the image
public class PinCustom : Pin
{
public string TypePointOfInterest { get; set; }
public string Icon { get; set; }
public Bitmap { get; set; }
//Here i create this variable to save a bitmap but i don't know if i do the things well
}
this is the icon .png i want to show in googlemaps
Pin Blue Image

To open your file and convert it to byte array:
string directory = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, Android.OS.Environment.DirectoryDownloads);
// or your image directory, just replace it
var stream = File.OpenWrite(Path.Combine(directory, "image.png"));
byte[] buff = ConvertStreamToByteArray(stream);
stream.Close();
public static byte[] ConvertStreamToByteArray(Stream stream)
{
byte[] byteArray = new byte[16 * 1024];
using (MemoryStream mStream = new MemoryStream())
{
int bit;
while ((bit = stream.Read(byteArray, 0, byteArray.Length)) > 0)
{
mStream.Write(byteArray, 0, bit);
}
return mStream.ToArray();
}
}
then, to pass this byte array to SKBitmap:
SKBitmap bmp = SKBitmap.Decode(buff);
EDIT:
If you want to try without ConvertStreamToByteArray():
byte[] buff = null;
stream.Write(buff, 0, buff.Length);
This Write will depend of the type of your stream. In this example, I'm using FileStream.
EDIT 2:
string resourceID = "image.png";
Assembly assembly = GetType().GetTypeInfo().Assembly;
using (Stream stream = assembly.GetManifestResourceStream(resourceID))
{
resourceBitmap = SKBitmap.Decode(stream);
SKBitmap bmp = SKImage.FromBitmap(resourceBitmap);
}
and then you can use this bitmap to draw and fill your SKCanvas:
canvas.DrawBitmap(bmp, 0, 0);

Use ffmpeg
command for this: ffmpeg -i image.png image.bmp

i have 5 types of pins (pins are the image .png) when i put the pins
in format .png
if you want to custom the pins in your map, you can simply use Custom Renderers to achieve this.
The icon used to represent a marker can be customized by calling the MarkerOptions.SetIcon method. This can be accomplished by overriding the CreateMarker method, which is invoked for each Pin that's added to the map:
protected override MarkerOptions CreateMarker(Pin pin)
{
var marker = new MarkerOptions();
marker.SetPosition(new LatLng(pin.Position.Latitude, pin.Position.Longitude));
marker.SetTitle(pin.Label);
marker.SetSnippet(pin.Address);
marker.SetIcon(BitmapDescriptorFactory.FromResource(Resource.Drawable.pin));
return marker;
}
If you want to display different icons, you can refer to the following code:
protected override MarkerOptions CreateMarker(Pin pin)
{
var marker = new MarkerOptions();
marker.SetPosition(new LatLng(pin.Position.Latitude, pin.Position.Longitude));
marker.SetTitle(pin.Label);
marker.SetSnippet(pin.Address);
var customPin = (Element as CustomMap).CustomPins.FirstOrDefault(p => p.Position == pin.Position);
if (customPin != null)
{
if (customPin.IconType == "corporate")
{
marker.SetIcon(BitmapDescriptorFactory.FromResource(Resource.Drawable.corporate));
}
else if (customPin.IconType == "pickup")
{
marker.SetIcon(BitmapDescriptorFactory.FromResource(Resource.Drawable.bus));
}
}
return marker;
}
For more, check:Customizing the Marker.

ObservableCollection doesnt virtualise data?

I want to add approx 600 images to my collection to show them in a Listview that virtualizes with Itemsstackpanel. If i didnt misread with virtualization its possible to load large datasets. My problem is that the collection can only hold around 150 images and then i get a OutOfMemory Exception. Is there something more to enable virtualization or is the problem that my Collection calls its propertyChanged Event for every image added?
The error is thrown on:
await pdfPage.RenderToStreamAsync(Imagestream);
and how i add to my collection:
for (uint i = convertedPageString; i < 200 + convertedPageString; i++)
{
Image img = await LoadPage(l_document, i);
collection.Add(img);
g_rootPage.ListViewControl.ItemsSource = collection;
}
convertedPageString is just the Page im starting on when the program is opened.
EDIT:
This is my function to get the Pages.
public async Task<Image> LoadPage(PdfDocument a_document, uint page)
{
Image l_image;
BitmapImage l_bitmap;
PdfPage pdfPage;
using (IRandomAccessStream Imagestream = new MemoryStream().AsRandomAccessStream())
{
using (pdfPage = a_document.GetPage(page))
{
await pdfPage.RenderToStreamAsync(Imagestream);
l_bitmap = new BitmapImage();
await l_bitmap.SetSourceAsync(Imagestream);
l_image = new Image();
l_bitmap.DecodePixelHeight = 1200;
l_bitmap.DecodePixelWidth = 1000;
l_image.Source = l_bitmap;
l_image.Margin = new Thickness(0, 5, 0, 10);
}
}
return l_image;
}
I forgot to mention that i open the application via the commandLine with a specified page and path.

C# EMGU 3.1 Image stitching method parameters

I am trying to stitch multiple images to single(panorama) image.
Following code working fine in EMGU-2.4 but in EMGU-3.1 I have a problem in passing parameters in stitch method.
// Collect all images
List<Image<Bgr, Byte>> sourceImages = new List<Image<Bgr, Byte>>();
for (int i = 1; i <7 ; i++)
{
string fileN = fl1 + "n (" + i.ToString() + ").jpg";
sourceImages.Add(new Image<Bgr, Byte>(fileN));
}
try
{
using (Stitcher stitcher = new Stitcher(false))
{
// Stitch images
Image<Bgr, Byte> result = stitcher.Stitch(sourceImages.ToArray());
Bitmap bm = result.ToBitmap();
bm.Save(fl1 + "resul.jpeg", ImageFormat.Jpeg);
}
}
finally
{
}
EMGU-3.1 documentation : stitch method contains new parameters like below
//
// Summary:
// Compute the panoramic images given the images
//
// Parameters:
// images:
// The input images. This can be, for example, a VectorOfMat
//
// pano:
// The panoramic image
//
// Returns:
// true if successful
public bool Stitch(IInputArray images, IOutputArray pano);
How to pass this two parameters in my existing code and what is this parameters for?
Please I am pretty new to EMGU

You could pass a Emgu.CV.Util.VectorOfMat as input and use a EMGU.CV.Mat to store the output, like this:
using (Stitcher stitcher = new Stitcher(false))
{
using (VectorOfMat vm = new VectorOfMat())
{
Mat result = new Mat();
vm.Push(sourceImages);
stitcher.Stitch(vm, result);
resultImageBox.Image = result; //Display the result
}
}
Note that the "resultImageBox" used above is a ImageBox from EMGU, but you could use a PictureBox to display result.Bitmap, for example.
This example was taken from the Stitching example provided by EMGU, you can find more information there

Sorry, I did not have 50 reputation hence I could not comment. Otherwise I wouldn't be posting here.
Using the below code, I encounter this error message: Argument 1 - cannot convert from 'System.Collections.Generic.List>'to 'Emgu.CV.Mat'. The error is from "vm.Push(sourceImages);"
using (Stitcher stitcher = new Stitcher(false))
{
using (VectorOfMat vm = new VectorOfMat())
{
Mat result = new Mat();
vm.Push(sourceImages);
stitcher.Stitch(vm, result);
resultImageBox.Image = result; //Display the result
}
}

Change PdfImage type (Syncfusion PDF)

So I'm using Syncfusion Controls for UWP XAML, and I'm trying to insert JPEGs into a PDF I'm creating, but PdfImage seems to always return bitmaps. Or at least images with bitmap-like file sizes.
Is there any way to ensure the images being inserted are of JPEG size? The images I'm inputting are JPEGs to begin with.
I'd be fine with bitmaps if I wasn't making PDFs of manga (Japanese comic books), i.e. the size per manga right now ranges from 50-150MB.
It's not a working sample, but here's what I'm using right now.
public async void SaveAsPdf(Stream fs, Manga manga)
{
var m = manga;
var c = m.Content;
if (fs.Length != 0) return;
var pdf = new PdfDocument();
var pages = await GetPages(m);
pdf.PageSettings.SetMargins(0);
pdf.FileStructure.IncrementalUpdate = true;
pdf.EnableMemoryOptimization = true;
pdf.Compression = PdfCompressionLevel.Best;
for (var pi = 0; pi < c.ContentPages; pi++)
{
var section = pdf.Sections.Add();
var mr = section.PageSettings.Margins = new PdfMargins();
mr.All = 0;
var page = section.Pages.Add();
var g = page.Graphics;
page.DefaultLayerIndex = 0;
var pu = pages[pi];
var client = new HttpClient();
var im = await client.GetAsync(pu);
var pdi = PdfImage.FromStream(im.Content.ReadAsStreamAsync().Result);
g.DrawImage(pdi, new PointF(0, 0), g.ClientSize);
await pdf.SaveAsync(fs);
}
await pdf.SaveAsync(fs);
pdf.DocumentInformation.Title = c.ContentName;
pdf.DocumentInformation.Author += string.Join(", ", c.ContentArtists.Select(x => x.Attribute));
pdf.DocumentInformation.Keywords += string.Join(", ", c.ContentTags.Select(x => x.Attribute)).Replace("\"", string.Empty);
pdf.Save(fs);
pdf.Close(true);
var toast = Notifications.NotifyMangaDownloaded(m);
ToastNotificationManager.CreateToastNotifier().Show(toast);
fs.Dispose();
}
I'd ask about the memory leak but it'd probably be best if I made another post for that.
Thanks in advance.
(I posted this on the Syncfusion forums but I felt like I might get a better response here)

Well, I refactored some of the methods and the memory leak ended up being the cause. Lesson learned: using statements are your friends.
To be a little more specific, I just created a file as a destination for the PDF, then called
using (Stream s = new FileStream(/*string*/>f.Path, FileMode.OpenOrCreate))
{
await Task.Run(() => SaveAsPdf(/*StorageFile*/f, /*Manga*/m));
}
Various other things needed to be moved around, but leaving the FileStream open ended up being the problem.

EmguCV - Face Recognition - 'Object reference not set' exception when using training set from Microsoft Access Database

I've been developing a face recognition application using EmguCV (C#). I got the whole thing working okay if I store the face images (training set) in simple windows folder. But, after I tried to migrate the face images to be stored in a Microsoft Access database, an 'object reference not set to an instance of an object' exception message often occurs (not always, but most of the time) when the application tries to recognize a face from the video feed.
Funny thing is, the recognition actually still works okay if the exception happens to not occur.
Here is the snippet of the code of my program, using windows folder and database:
Reading the stored images from a Windows Folder
private void FaceRecognition_Load(object sender, EventArgs e)
{
//if capture is not created, create it now
if (capture == null)
{
try
{
capture = new Capture();
}
catch (NullReferenceException excpt)
{
MessageBox.Show(excpt.Message);
}
}
if (capture != null)
{
if (captureInProgress)
{
Application.Idle -= ProcessFrame;
}
else
{
Application.Idle += ProcessFrame;
}
captureInProgress = !captureInProgress;
}
#endregion
{
// adjust path to find your xml at loading
haar = new HaarCascade("haarcascade_frontalface_default.xml");
try
{
//Load of previus trainned faces and labels for each image
string Labelsinfo = File.ReadAllText(Application.StartupPath + "\\TrainedFaces\\TrainedLabels.txt");
string[] Labels = Labelsinfo.Split('%');
NumLabels = Convert.ToInt16(Labels[0]);
ContTrain = NumLabels;
string LoadFaces;
for (int tf = 1; tf < NumLabels + 1; tf++)
{
LoadFaces = "face" + tf + ".bmp";
trainingImages.Add(new Image<Gray, byte>(Application.StartupPath + "\\TrainedFaces\\" + LoadFaces));
labels.Add(Labels[tf]);
}
}
catch (Exception error)
{
//MessageBox.Show(e.ToString());
MessageBox.Show("Nothing in binary database, please add at least a face(Simply train the prototype with the Add Face Button).", "Triained faces load", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
}
}
}
Reading the stored images from a Microsoft Access Database
private void connectToDatabase()
{
DBConnection.ConnectionString = #"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=FacesDatabase.mdb";
DBConnection.Open();
dataAdapter = new OleDbDataAdapter("Select * from TrainingSet1", DBConnection);
dataAdapter.Fill(localDataTable);
if (localDataTable.Rows.Count != 0)
{
numOfRows = localDataTable.Rows.Count;
}
}
private void FaceRecognition_Load(object sender, EventArgs e)
{
//if capture is not created, create it now
if (capture == null)
{
try
{
capture = new Capture();
}
catch (NullReferenceException excpt)
{
MessageBox.Show(excpt.Message);
}
}
if (capture != null)
{
if (captureInProgress)
{
Application.Idle -= ProcessFrame;
}
else
{
Application.Idle += ProcessFrame;
}
captureInProgress = !captureInProgress;
}
#endregion
{
// adjust path to find your xml at loading
haar = new HaarCascade("haarcascade_frontalface_default.xml");
connectToDatabase();
Bitmap bmpImage;
for (int i = 0; i < numOfRows; i++)
{
byte[] fetchedBytes = (byte[])localDataTable.Rows[i]["FaceImage"];
MemoryStream stream = new MemoryStream(fetchedBytes);
bmpImage = new Bitmap(stream);
trainingImages.Add(new Emgu.CV.Image<Gray, Byte>(bmpImage));
String faceName = (String)localDataTable.Rows[i]["Name"];
labels.Add(faceName);
}
}
}
The face recognition function that causes the exception (exactly the same both when using windows folder and Access database):
private void ProcessFrame(object sender, EventArgs arg)
{
Image<Bgr, Byte> ImageFrame = capture.QueryFrame();
Image<Gray, byte> grayframe = ImageFrame.Convert<Gray, byte>();
MinNeighbors = int.Parse(comboBoxMinNeighbors.Text);
WindowsSize = int.Parse(textBoxWinSiz.Text);
ScaleIncreaseRate = Double.Parse(comboBoxMinNeighbors.Text);
var faces = grayframe.DetectHaarCascade(haar, ScaleIncreaseRate, MinNeighbors,
HAAR_DETECTION_TYPE.DO_CANNY_PRUNING,
new Size(WindowsSize, WindowsSize))[0];
if (faces.Length > 0)
{
Bitmap BmpInput = grayframe.ToBitmap();
Graphics FaceCanvas;
foreach (var face in faces)
{
t = t + 1;
result = ImageFrame.Copy(face.rect).Convert<Gray, byte>().Resize(100, 100, Emgu.CV.CvEnum.INTER.CV_INTER_CUBIC);
ImageFrame.Draw(face.rect, new Bgr(Color.Red), 2);
ExtractedFace = new Bitmap(face.rect.Width, face.rect.Height);
FaceCanvas = Graphics.FromImage(ExtractedFace);
FaceCanvas.DrawImage(BmpInput, 0, 0, face.rect, GraphicsUnit.Pixel);
ImageFrame.Draw(face.rect, new Bgr(Color.Red), 2);
if (trainingImages.ToArray().Length != 0)
{
MCvTermCriteria termCrit = new MCvTermCriteria(ContTrain, 0.001);
EigenObjectRecognizer recognizer = new EigenObjectRecognizer(
trainingImages.ToArray(),
labels.ToArray(),
3000,
ref termCrit);
try
{
name = recognizer.Recognize(result).Label;
}
catch (Exception error)
{
MessageBox.Show(error.ToString());
}
ImageFrame.Draw(name, ref font, new Point(face.rect.X - 2, face.rect.Y - 2), new Bgr(Color.LightGreen));
}
}
}
CamImageBox.Image = ImageFrame;
}
Here is the screenshot of the exception message:
http://i.imgur.com/DvAhABK.jpg
Line 146 where the exception occurs is this line of the ProcessFrame function:
name = recognizer.Recognize(result).Label;
I tried searching for similar problems in the internet, and found these:
'Object reference not set to instance of an object' error when trying to upload image to database
Object reference not set to an instance of an object #5
C# Error 'Object Reference Not Set To An Instance Of An Object'
C#, "Object reference not set to an instance of an object." error
Most of them suggests to check if any of the involved variable is null. I've checked the involved variable, and indeed the exception occurs when the recognizer.Recognize(result) statement returns null.
So my question is, why does that statement often return null when I use training images from the database, while it never returns null when I use training images from windows folder?

Check your fetchedBytes array to see if you are consistently getting just a stream of bytes representing a BMP image (starting with 0x42 0x4D), or if there may be "other stuff" in there, too.
Depending on how the BMP data was inserted into the Access database it may contain an OLE "wrapper". For example, an 8x8 24-bit BMP image of pure red is saved by MSPAINT.EXE like this
If I copy that file and paste it into a Bound Object Frame in an Access form then Access wraps the BMP data in some "OLE stuff" before writing it to the table. Later, if I try to retrieve the BMP image via code, using something like this...
Sub oleDumpTest()
Dim rst As ADODB.Recordset, ads As ADODB.Stream
Set rst = New ADODB.Recordset
rst.Open "SELECT * FROM TrainingSet1 WHERE ID = 1", Application.CurrentProject.Connection
Set ads = New ADODB.Stream
ads.Type = adTypeBinary
ads.Open
ads.Write rst("FaceImage").Value
rst.Close
Set rst = Nothing
ads.SaveToFile "C:\Users\Gord\Pictures\oleDump_red."
ads.Close
Set ads = Nothing
End Sub
...then the resulting file also contains the OLE "wrapper"...
...and obviously is not a valid stand-alone BMP file. If I rename that file to give it a .bmp extension and try to open it in Paint, I get
So maybe (some of) the [FaceImage] objects in your database are not raw BMP data, and perhaps the other software is rejecting them (or simply not able to understand them).
Edit
Another possible issue is that when you get the images from files in a folder you hand the Image object a string containing the file path...
trainingImages.Add(new Image<Gray, byte>(Application.StartupPath + "\\TrainedFaces\\" + LoadFaces));
...but when you try to retrieve the images from the database you hand the same object a Bitmap object
MemoryStream stream = new MemoryStream(fetchedBytes);
bmpImage = new Bitmap(stream);
trainingImages.Add(new Emgu.CV.Image<Gray, Byte>(bmpImage));
I have no way of knowing whether the Emgu.CV.Image object might behave differently depending on the type of object it is given, but a quick+dirty workaround might be to write bmpImage to a temporary file, hand trainingImages.Add the path to that file, and then delete the file.

Finally made it!! just one more day of coding helped me to got the problem solved:
public void ProcessRequest(HttpContext context)
{
_httpContext = context;
var imageid = context.Request.QueryString["Image"];
if (imageid == null || imageid == "")
{
imageid = "1";
}
using (WebClient wc = new WebClient())
{
// Handler retrieves the image from database and load it on the stream
using (Stream s = wc.OpenRead("http://mypageurl/Image.ashx?Image=" + imageid))
{
using (Bitmap bmp = new Bitmap(s))
{
AddFace(bmp);
}
}
}
}
public void AddFace(Bitmap image)
{
var faceImage = DetectFace(image);
if (faceImage != null)
{
var stream = new MemoryStream();
faceImage.Save(stream, ImageFormat.Bmp);
stream.Position = 0;
byte[] data = new byte[stream.Length];
stream.Read(data, 0, (int)stream.Length);
_httpContext.Response.Clear();
_httpContext.Response.ContentType = "image/jpeg";
_httpContext.Response.BinaryWrite(data);
}
}
private Bitmap DetectFace(Bitmap faceImage)
{
var image = new Image<Bgr, byte>(faceImage);
var gray = image.Convert<Gray, Byte>();
string filePath = HttpContext.Current.Server.MapPath("haarcascade_frontalface_default.xml");
var face = new HaarCascade(filePath);
MCvAvgComp[][] facesDetected = gray.DetectHaarCascade(face, 1.1, 10, HAAR_DETECTION_TYPE.DO_CANNY_PRUNING, new Size(20, 20));
Image<Gray, byte> result = null;
foreach (MCvAvgComp f in facesDetected[0])
{
//draw the face detected in the 0th (gray) channel with blue color
image.Draw(f.rect, new Bgr(Color.Blue), 2);
result = image.Copy(f.rect).Convert<Gray, byte>();
break;
}
if (result != null)
{
result = result.Resize(200, 200, INTER.CV_INTER_CUBIC);
return result.Bitmap;
}
return null;
}
public bool IsReusable
{
get { return false; }
}

I couldnt make it work from reading a direct Stream from the the Database where the images are located but your workaround, saving the images to a local folder, worked for me, thx a lot for sharing.Here's my demo page where you load files from DB: http://www.edatasoluciones.com/FaceDetection/FaceDataBase