I need to send an image into a byte array using c++/cli. The image is initially in Iplimage format.
int img_sz1 = img1->width * img1->height * img1->nChannels;
array <Byte>^ hh1 = gcnew array<Byte> (img_sz1);
Marshal::Copy( (IntPtr)img->imageData, hh1, 0, img_sz1 );
and it was working fine.
I added the encoding step to send it as jpeg
CvMat* buf1 = cvEncodeImage(".jpeg", img1, jpeg_params);
img_sz1=buf1->width*buf1->height
Marshal::Copy( (IntPtr)buf1, hh1, 0, img_sz1 );
and now it compiles fine but gives me the error at the marshal:copy line
An unhandled exception of type 'System.AccessViolationException' occurred in
mscorlib.dll. Additional information: Attempted to read or write protected memory.
Any help is very appreciated.
The return of cvEncodeImage is a single-row matrix, containing the encoded image data. What you're copying now is the struct itself, e.g., the width field, the height field, etc. I believe you need to copy from buf1->data instead.
Related
I want to load an image in c++ opencv that comes from a postgresql database.
The image, jpg extension, is stored as a binary data (bytea type) in the base, that I can access thanks to libpqxx.
The problem is that I do not know how to convert the data into a cv::Mat instance. With a regular image I could use imread('myImage.jpg', ...), but in this case I cannot even load the database image in the data attribute of Mat because it is jpeg and not bmp.
Any idea ? Is there some opencv method I could use that could understand directly the binary data and convert it to the appropriate structure ? the imdecode() functions seems to be used for bitmap datas.
edit : Berak, using a vector the imdecode function returns null Matrice What happens "If the buffer is too short or contains invalid data, the empty matrix/image is returned." Here is the code :
pqxx::result r=bdd::requete("SELECT image FROM lrad.img WHERE id=3",1);//returns the bytea image in r[0]["image"]
const char* buffer=r[0]["image"].c_str();
vector<uchar>::size_type size = strlen((const char*)buffer);
vector<uchar> jpgbytes(buffer, buffer+size);
Mat img = imdecode(jpgbytes, CV_LOAD_IMAGE_COLOR);
//jpgbytes.size()=1416562 img.size()=[0 x 0]
What am I missing ?
still, use imdecode . it can handle png,jpg,bmp,ppm,webp,jp2,exr, but no gif.
vector<uchar> jpgbytes; // from your db
Mat img = imdecode(jpgbytes);
(you should do the same for bmp or any other supported formats, don't mess with Mat's raw data pointers!)
Ok I have the process to convert a bytea data to a cv::Mat, here is the code.
inline int dec(uchar x){ //convert uchar to int
if (x>='0'&&x<='9') return (x-'0');
else if (x>='a'&&x<='f') return (x-'a'+10);
else if (x>='A'&&x<='F') return (x-'A'+10);
return 0;
}
cv::Mat bytea2Mat(const pqxx::result::field& f){
const char* buffer=f.c_str();
vector<uchar>::size_type size = strlen((const char*)buffer);
vector<uchar> jpgbytes(size/2-1);
for (size_t i=0; i!=size/2-1;i++) {
jpgbytes[i]=(dec(buffer[2*(i+1)])<<4)+dec(buffer[2*(i+1)+1]);
}
cout <<size/2<<";"<<jpgbytes.size()<<endl;
return imdecode(jpgbytes, CV_LOAD_IMAGE_COLOR);
}
The bytea output is encrypted as a char* looking like "\x41204230", for an original input string of "a b0" in hexa form. (the \x may not be present according to the data input)
to get the original data you have to calculate the original input from the two char, ('4','1'= 0x41=65). The vector is half the size of the char*.
I'm using DirectShow to access a video stream, and then using the SampleGrabber filter and interface to get samples from each frame for further image processing. I'm using a callback, so it gets called after each new frame. I've basically just worked from the PlayCap sample application and added a sample filter to the graph.
The problem I'm having is that I'm trying to display the grabbed samples on a different OpenCV window. However, when I try to cast the information in the buffer to an IplImage, I get a garbled mess of pixels. The code for the BufferCB call is below, sans any proper error handling:
STDMETHODIMP BufferCB(double Time, BYTE *pBuffer, long BufferLen)
{
AM_MEDIA_TYPE type;
g_pGrabber->GetConnectedMediaType(&type);
VIDEOINFOHEADER *pVih = (VIDEOINFOHEADER *)type.pbFormat;
BITMAPINFO* bmi = (BITMAPINFO *)&pVih->bmiHeader;
BITMAPINFOHEADER* bmih = &(bmi->bmiHeader);
int channels = bmih->biBitCount / 8;
mih->biPlanes = 1;
bmih->biBitCount = 24;
bmih->biCompression = BI_RGB;
IplImage *Image = cvCreateImage(cvSize(bmih->biWidth, bmih->biHeight), IPL_DEPTH_8U, channels);
Image->imageSize = BufferLen;
CopyMemory(Image->imageData, pBuffer, BufferLen);
cvFlip(Image);
//openCV Mat creation
Mat cvMat = Mat(Image, true);
imshow("Display window", cvMat); // Show our image inside it.
waitKey(2);
return S_OK;
}
My question is, am I doing something wrong here that will make the image displayed look like this:
Am I missing header information or something?
The quoted code is a part of the solution. You create here an image object of certain width/height with 8-bit pixel data and unknown channel/component count. Then you copy data from another buffer of unknown format.
The only chance for it to work well is that all unknowns amazingly match without your effort. So you basically need to start with checking what media type is exactly on Sample Grabber's input pin. Then, if it is not what you wanted, you have to update your code respectively. It might also be important what is the downstream connection of the SG, and whether it is connected to video renderer in particular.
How do I convert a WriteableBitmap into a BitmapImage object in Silverlight5 ?
So far, here is my attempt in converting a WriteableBitmap into a BitmapImage; however, it doesn't work.
No exception is thrown, the resulting BitmapImage is simply an 'empty' object with no data; both PixelHeight and PixelWidth are zero:
public BitmapImage Convert(WriteableBitmap wb)
{
int[] p = wb.Pixels;
int len = p.Length * 4;
byte[] result = new byte[len];
Buffer.BlockCopy(p, 0, result, 0, len);
MemoryStream ms = new MemoryStream(result);
BitmapImage bi = new BitmapImage();
bi.SetSource(ms);
// bi.PixelHeight and bi.PixelWidth are zero.
return bi; // pretty much an empty image.
}
Cross-post here: http://social.msdn.microsoft.com/Forums/silverlight/en-US/0a0c833b-8e68-4c8d-871a-d0805d84ba16/writeablebitmap-to-bitmapimage?forum=silverlightpivotviewer
To summarize the discussion on your cross-post:
Yes, you have to convert your image to either png or jpg to create a BitmapImage.
The stream the BitmapImage expects is an encoded image file, but the bytes you get from WriteableBitmap is an uncompressed, raw ARGB pixel format.
In order to produce either a png or a jpg you have to use either link against a library that can do this, or use Stegman's one-page png encoder (that doesn't actually compress anything).
Since this was already suggested in the forum you asked but you noticed that the link is broken, I put a public gist on github from the copy I had locally.
I have a raw file which contains a header of 5 bytes containing the number of rows and columns in first two bits each . The 5th byte contains the number of bits for each pixel in the image which is 8 bits in all cases. The image data follows after that.
Since I am new to openCV, i want to ask how to view this RAW image file as an greyscale image using C++?
I know how to read binary data in C++ and have stored the image as a 2-D unsigned char array (since each pixel is 8 bit).
Can anyone please tell me how to view this data as image using openCV ?
I am using the below code , but getting a completely weird image :
void openRaw() {
cv::Mat img(numRows, numCols,CV_8U,&(image[0][0]));
//img.t();
cv::imshow("img",img);
cv::waitKey();
}
Any help will be greatly appreciated.
Thanks,
Rohit
You have to convert it to an IplImage.
If you want to see it as a pure grey-scale image, its actually rather easy.
Example code I use in one application:
CvSize mSize;
mSize.height = 960;
mSize.width = 1280;
IplImage* image1 = cvCreateImage(mSize, 8, 1);
memcpy( image1->imageData, rawDataPointer, sizeOfImage);
cvNamedWindow( "corners1", 1 );
cvShowImage( "corners1", image1 );
At that point you have a valid IplImage, which you can then display. (last 2 lines of code display it)
If the image is bayer-tiled, you will have to convert to RGB.
c++ notation:
cv::Mat img(rows,cols,CV_8U,ptrToDat);
cv::imwhow("img",img);
cv::waitkey();
*data should be saved columwise, otherewise use:
cv::Mat img(cols,rows,CV_8U,ptrToDat);
img=img.t();
cv::imwhow("img",img);
cv::waitkey();
Given the following
Bitmap raw image data in char array
Image width and height
Path wzAppDataDirectory in std::wstring generated using the following code
// Get a good path.
wchar_t wzAppDataDirectory[MAX_PATH];
wcscpy_s( wzAppDataDirectory, MAX_PATH, Windows::Storage::ApplicationData::Current->LocalFolder->Path->Data() );
wcscat_s( wzAppDataDirectory, MAX_PATH, (std::wstring(L"\\") + fileName).c_str() );
How can we save the image as JPG? (Include encoding as well as the char array is raw bitmap form)
Code example is very much appreciated.
You'll need to use a library to encode the JPEG. Some possibilities are the Independent JPEG Group's jpeglib, stb_image, or DevIL.
This is an example code which I obtained from my friend.
It uses OpenCV's Mat data structure. Note that, you need to ensure the unsigned char data array within cv::Mat is in continuous form. cv::cvtColor will do the trick (Or, cv::Mat.clone).
Take note, do not use OpenCV's imwrite. As at current time of writing, imwrite doesn't pass Windows Store Certification Test. It is using several APIs, which is prohibited in WinRT.
void SaveMatAsJPG(const cv::Mat& mat, const std::wstring fileName)
{
cv::Mat tempMat;
cv::cvtColor(mat, tempMat, CV_BGR2BGRA);
Platform::String^ pathName = ref new Platform::String(fileName.c_str());
task<StorageFile^>(ApplicationData::Current->LocalFolder->CreateFileAsync(pathName, CreationCollisionOption::ReplaceExisting)).
then([=](StorageFile^ file)
{
return file->OpenAsync(FileAccessMode::ReadWrite);
}).
then([=](IRandomAccessStream^ stream)
{
return BitmapEncoder::CreateAsync(BitmapEncoder::JpegEncoderId, stream);
}).
then([=](BitmapEncoder^ encoder)
{
const Platform::Array<unsigned char>^ pixels = ref new Platform::Array<unsigned char>(tempMat.data, tempMat.total() * tempMat.channels());
encoder->SetPixelData(BitmapPixelFormat::Bgra8, BitmapAlphaMode::Ignore, tempMat.cols , tempMat.rows, 96.0, 96.0, pixels);
encoder->FlushAsync();
});
}