I'm trying to develop a small C++/CLI wrapper around OpenCV for use in a C# application. I can't use Emgu since it's for a commercial application.
I'm facing a problem when I'm trying to convert from System.Drawing.Bitmap to OpenCV Mat.
I have the following code:
cv::Mat BitmapToMat(System::Drawing::Bitmap^ bitmap)
{
System::Drawing::Rectangle blank = System::Drawing::Rectangle(0, 0, bitmap->Width, bitmap->Height);
System::Drawing::Imaging::BitmapData^ bmpdata = bitmap->LockBits(blank, System::Drawing::Imaging::ImageLockMode::ReadWrite, System::Drawing::Imaging::PixelFormat::Format24bppRgb);
cv::Mat cv_img(cv::Size(bitmap->Width, bitmap->Height), CV_8UC3, bmpdata->Scan0.ToPointer(), cv::Mat::AUTO_STEP);
bitmap->UnlockBits(bmpdata);
return cv_img;
}
I'm using it in cpp file to test out the generated Mat like this:
Mat image = BitmapToMat(templateImage);
cv::imwrite("some2.jpg", image);
But the image produced is completely distorted (see images)
INPUT BITMAP IMAGE
RESULT MAT IMAGE SAVED TO FILE
Windows bitmaps are padded. You want to calculate "width in bytes" of the bitmap row, and supply that instead of cv::Mat::AUTO_STEP:
int wb = ((bitmap->Width * 24 + 31) / 32) * 4;
cv::Mat cv_img(cv::Size(bitmap->Width, bitmap->Height),
CV_8UC3, bmpdata->Scan0.ToPointer(), wb);
Related
If I have an opencv image that I read from a png file like this:
cv::Mat img = cv::imread("/to/path/test.png");
how do I get that image in bytes? I know using img.data returns an unsigned char* but that is not what I need. Any suggestions?
If I got your question right, you want, for example, a 250*250 image to return a 250*250 matrix so I would suggest using grey-scale instead of BGR
imgData = cv2.imread(path, 0)
I believe this is written in C++ like this
cv::Mat img = cv::imread(file_name);//It returns a matrix object
cv::Mat graymat;
cvtColor(img, graymat,cv::COLOR_BGR2GRAY);
I am programming in Qt environment and I have a Mat image with size 2592x2048 and I want to resize it to the size of a "label" that I have. But when I want to show the image, I have to multiply the width by 3, so the image is shown in its correct size. Is there any explanation for that?
This is my code:
//Here I get image from the a buffer and save it into a Mat image.
//img_width is 2592 and img_height is 2048
Mat image = Mat(cv::Size(img_width, img_height), CV_8UC3, (uchar*)img, Mat::AUTO_STEP);
Mat cimg;
double r; int n_width, n_height;
//Get the width of label (lbl) into which I want to show the image
n_width = ui->lbl->width();
r = (double)(n_width)/img_width;
n_height = r*(img_height);
cv::resize(image, cimg, Size(n_width*3, n_height), INTER_AREA);
Thanks.
The resize function works well, because if you save the resized image as a file is displayed correctly. Since you want to display it on QLabel, I assume you have to transform your image to QImage first and then to QPixmap. I believe the problem lies either in the step or the image format.
If we ensure the image data passed in
Mat image = Mat(cv::Size(img_width, img_height), CV_8UC3, (uchar*)img, Mat::AUTO_STEP);
are indeed an RGB image, then below code should work:
ui->lbl->setPixmap(QPixmap::fromImage(QImage(cimg.data, cimg.cols, cimg.rows, *cimg.step.p, QImage::Format_RGB888 )));
Finally, instead of using OpenCV, you could construct a QImage object using the constructor
QImage((uchar*)img, img_width, img_height, QImage::Format_RGB888)
and then use the scaledToWidth method to do the resize. (beware thought that this method returns the scaled image, and does not performs the resize operation to the image per se)
I am trying to rotate an image in x, y and z axis as in this.
The image should not be cropped while rotating So I am doing this
Mat src = imread("path");
int diagonal = (int)sqrt(src.cols*src.cols+src.rows*src.rows);
int newWidth = diagonal;
int newHeight =diagonal;
Mat targetMat(newWidth, newHeight, src.type());
I am creating a bigger image targetMat. The input image is a png image.
But I want this image as a transparent image. So I tried this
Mat targetMat(newWidth, newHeight, src.type(), cv::Scalar(0,0,0,0));
But the output image was
What I need is (Transparent image is here)
So what change do I have to do?
The problem is, that your input image is type CV_8UC3 but you need CV_8UC4 to use the alpha channel. So try Mat targetMat(newHeight, newWidth, CV_8UC4, cv::Scalar(0,0,0,0)); or cvtColor of src before creation of new mat
To use your original image, there are two possibilities:
use cv::cvtColor(src, src, CV_BGR2BGRA) (and adjust later code to use a 4 channel matrix - cv::Vec4b instead of cv::Vec3b etc)
if your input file is a .png with alpha channel you can use the CV_LOAD_IMAGE_ANYDEPTH (hope this is the right one) flag to load it as a CV_xxC4 image (might be 16 bit too) and to use the original alpha values.
I'm using OpenCV to extract a subimage of a scanned document and would like to use tesseract to perform OCR over this subimage.
I found out that I can use two methods for text recognition in tesseract, but so far I wasn't able to find a working solution.
A.) How can I convert a cv::Mat into a PIX*?
(PIX* is a datatype of leptonica)
Based on vasiles code below, this is essentially my current code:
cv::Mat image = cv::imread("c:/image.png");
cv::Mat subImage = image(cv::Rect(50, 200, 300, 100));
int depth;
if(subImage.depth() == CV_8U)
depth = 8;
//other cases not considered yet
PIX* pix = pixCreateHeader(subImage.size().width, subImage.size().height, depth);
pix->data = (l_uint32*) subImage.data;
tesseract::TessBaseAPI tess;
STRING text;
if(tess.ProcessPage(pix, 0, 0, &text))
{
std::cout << text.string();
}
While it doesn't crash or anything, the OCR result still is wrong. It should recognize one word of my sample image, but instead it returns some non-readable characters.
The method PIX_HEADER doesn't exist, so I used pixCreateHeader, but it doesn't take the number of channels as an argument. So how can I set the number of channels?
B.) How can I use cv::Mat for TesseractRect() ?
Tesseract offers another method for text recognition with this signature:
char * TessBaseAPI::TesseractRect (
const UINT8 * imagedata,
int bytes_per_pixel,
int bytes_per_line,
int left,
int top,
int width,
int height
)
Currently I am using the following code, but it also returns non-readable characters (although different ones than from the code above.
char* cr = tess.TesseractRect(
subImage.data,
subImage.channels(),
subImage.channels() * subImage.size().width,
0,
0,
subImage.size().width,
subImage.size().height);
tesseract::TessBaseAPI tess;
cv::Mat sub = image(cv::Rect(50, 200, 300, 100));
tess.SetImage((uchar*)sub.data, sub.size().width, sub.size().height, sub.channels(), sub.step1());
tess.Recognize(0);
const char* out = tess.GetUTF8Text();
For Anybody using the JavaCPP presets of OpenCV/Tesseract, here is what works
Mat img = imread("file.jpg");
Mat gray = new Mat();
cvtColor(img, gray, CV_BGR2GRAY);
// api is a Tesseract client which is initialised
api.SetImage(gray.data().asBuffer(),gray.size().width(),gray.size().height(),gray.channels(),gray.size1())
cv::Mat image = cv::imread(argv[1]);
cv::Mat gray;
cv::cvtColor(image, gray, CV_BGR2GRAY);
PIX *pixS = pixCreate(gray.size().width, gray.size().height, 8);
for(int i=0; i<gray.rows; i++)
for(int j=0; j<gray.cols; j++)
pixSetPixel(pixS, j,i, (l_uint32) gray.at<uchar>(i,j));
First, make a deep copy of your subImage, so that it will be stored in a coninuous memory block:
cv::Mat subImage = image(cv::Rect(50, 200, 300, 100)).clone();
Then, init a PIX headed (I don't know how) with the correct parameters.
// ???? Put your own constructor here.
PIX* pix = new PIX_HEADER(width, height, channels, depth);
OR, create it manually:
PIX pix;
pix.width = subImage.width;
...
Then set the pix data pointer to the subImage data pointer
pix.data = subImage.data;
Finally, make sure your subImage objects does not go out of scope before you finish your work with pix.
I would like to know how to convert an RGB image into a black & white (binary) image.
After conversion, how can I save the modified image to disk?
AFAIK, you have to convert it to grayscale and then threshold it to binary.
1. Read the image as a grayscale image
If you're reading the RGB image from disk, then you can directly read it as a grayscale image, like this:
// C
IplImage* im_gray = cvLoadImage("image.jpg",CV_LOAD_IMAGE_GRAYSCALE);
// C++ (OpenCV 2.0)
Mat im_gray = imread("image.jpg",CV_LOAD_IMAGE_GRAYSCALE);
2. Convert an RGB image im_rgb into a grayscale image: Otherwise, you'll have to convert the previously obtained RGB image into a grayscale image
// C
IplImage *im_rgb = cvLoadImage("image.jpg");
IplImage *im_gray = cvCreateImage(cvGetSize(im_rgb),IPL_DEPTH_8U,1);
cvCvtColor(im_rgb,im_gray,CV_RGB2GRAY);
// C++
Mat im_rgb = imread("image.jpg");
Mat im_gray;
cvtColor(im_rgb,im_gray,CV_RGB2GRAY);
3. Convert to binary
You can use adaptive thresholding or fixed-level thresholding to convert your grayscale image to a binary image.
E.g. in C you can do the following (you can also do the same in C++ with Mat and the corresponding functions):
// C
IplImage* im_bw = cvCreateImage(cvGetSize(im_gray),IPL_DEPTH_8U,1);
cvThreshold(im_gray, im_bw, 128, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);
// C++
Mat img_bw = im_gray > 128;
In the above example, 128 is the threshold.
4. Save to disk
// C
cvSaveImage("image_bw.jpg",img_bw);
// C++
imwrite("image_bw.jpg", img_bw);
This seemed to have worked for me!
Mat a_image = imread(argv[1]);
cvtColor(a_image, a_image, CV_BGR2GRAY);
GaussianBlur(a_image, a_image, Size(7,7), 1.5, 1.5);
threshold(a_image, a_image, 100, 255, CV_THRESH_BINARY);
I do something similar in one of my blog postings. A simple C++ example is shown.
The aim was to use the open source cvBlobsLib library for the detection
of spot samples printed to microarray slides, but the images have to be
converted from colour -> grayscale -> black + white as you mentioned, in order to achieve this.
A simple way of "binarize" an image is to compare to a threshold:
For example you can compare all elements in a matrix against a value with opencv in c++
cv::Mat img = cv::imread("image.jpg", CV_LOAD_IMAGE_GRAYSCALE);
cv::Mat bw = img > 128;
In this way, all pixels in the matrix greater than 128 now are white, and these less than 128 or equals will be black
Optionally, and for me gave good results is to apply blur
cv::blur( bw, bw, cv::Size(3,3) );
Later you can save it as said before with:
cv::imwrite("image_bw.jpg", bw);
Simple binary threshold method is sufficient.
include
#include <string>
#include "opencv/highgui.h"
#include "opencv2/imgproc/imgproc.hpp"
using namespace std;
using namespace cv;
int main()
{
Mat img = imread("./img.jpg",0);//loading gray scale image
threshold(img, img, 128, 255, CV_THRESH_BINARY);//threshold binary, you can change threshold 128 to your convenient threshold
imwrite("./black-white.jpg",img);
return 0;
}
You can use GaussianBlur to get a smooth black and white image.