I'm new to OpenCV and I've done a small POC for reading an image from some URL.
I'm reading the image from an URL using video capture. The code is as follows:
VideoCapture vc;
vc.open("http://files.kurento.org/img/mario-wings.png");
if(vc.isOpened() && vc.grab())
{
cv::Mat logo;
vc.retrieve(logo);
cv::namedWindow("t");
imwrite( "mario-wings-opened.png", logo);
cv::imshow("t", logo);
cv::waitKey(0);
vc.release();
}
This image is not opened correctly, possibly due to alpha channel.
What is the way to preserve alpha channel and get the image correctly?
Any help is appreciated.
-Thanks
Expected output
Actual output
if you are only loading an image, I recommend you to use imread instead, also, you will need to specified the second parameter of imread to load the alpha channel too, that is CV_LOAD_IMAGE_UNCHANGED or cv::IMREAD_UNCHANGED, depending on the version (in the worst case a -1 also works).
As far as I know, the VideoCaptureclass do not load images/video with a 4th channel. Since you are using a web url, loading the image won't work with imread, but you may use any method to download the data (curl for example) and then use imdecode with the data buffer to get the cv::Mat. OpenCV is a library for image processing, not for downloading images.
If you wanna draw it over another image you can do that:
/**
* #brief Draws a transparent image over a frame Mat.
*
* #param frame the frame where the transparent image will be drawn
* #param transp the Mat image with transparency, read from a PNG image, with the IMREAD_UNCHANGED flag
* #param xPos x position of the frame image where the image will start.
* #param yPos y position of the frame image where the image will start.
*/
void drawTransparency(Mat frame, Mat transp, int xPos, int yPos) {
Mat mask;
vector<Mat> layers;
split(transp, layers); // seperate channels
Mat rgb[3] = { layers[0],layers[1],layers[2] };
mask = layers[3]; // png's alpha channel used as mask
merge(rgb, 3, transp); // put together the RGB channels, now transp insn't transparent
transp.copyTo(frame.rowRange(yPos, yPos + transp.rows).colRange(xPos, xPos + transp.cols), mask);
}
Related
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)
This is mainly a C++ variable/pointer handling/casting question.
I am trying to apply one of the openCV library image filters to a depth Image from the Kinect v2 SDK (16bit grayscale, values between 0 and 8092).
I want to do this after getting the depth image but BEFORE using the kinect SDK to do rgb-depth registration and conversion to a point cloud. Therefore I want the final filtered image/array to be of the same type as I received before filtering so I can pass it back to the Kinect SDK.
Initial code:
Get the kinect depth frame as a pointer
UINT nBufferSize = nDepthFrameHeight * nDepthFrameWidth;
hr = pDepthFrame->CopyFrameDataToArray(nBufferSize, pDepth);
create 2 matrices along with the conversion between the 16bit and 8bit(openCV works with 8bit greyscale)
Mat depthMat(height, width, CV_16UC1, depth); // from kinect
Mat depthf(height, width, CV_8UC1);
depthMat.convertTo(depthf, CV_8UC1, 255.0/2048.0);
imshow("original-depth", depthf);
const unsigned char noDepth = 0; // change to 255, if values no depth uses max value
Mat temp, temp2;
1 step - downsize for performance, use a smaller version of depth image
Mat small_depthf;
resize(depthf, small_depthf, Size(), 0.2, 0.2);
2 step - inpaint only the masked "unknown" pixels
cv::inpaint(small_depthf, (small_depthf == noDepth), temp, 5.0, INPAINT_TELEA);
3 step - upscale to original size and replace inpainted regions in original depth image
resize(temp, temp2, depthf.size());
temp2.copyTo(depthf, (depthf == noDepth)); // add to the original signal
imshow("depth-inpaint", depthf); // show results
Problematic Part:
When I try to reverse the process (even with loss of information for now)
cv::Mat newDepth(nDepthFrameHeight, nDepthFrameWidth, CV_16UC1);
depthf.convertTo(newDepth, CV_16UC1, 8092.0 / 255.0);
I have found no way to convert these cv::Mat types back to *ushort (*UINT16 in this case).
I have tried things like reinterpret_cast, depthf.data and depthf.ptr() but it keeps showing uchar when hovering over the final data, unless I force it like in the ptr case above, in which case it crashes.
Any ideas?
P.S.: Code works flawlessly if I don't try to filter the depth. Also, crash occurs when the SDK tries to map color and depth and tries to use pDepth in
pCoordinateMapper->MapColorFrameToDepthSpace(nDepthFrameWidth * nDepthFrameHeight, pDepth, nColorFrameWidth * nColorFrameHeight, (DepthSpacePoint*)pDepthSpacePoints);
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.
The problem is solved....I used cvGet2D,below is the sample code
CvScalar s;
s=cvGet2D(src_Image,pixel[i].x,pixel[i].y);
cvSet2D(dst_Image,pixel[i].x,pixel[i].y,s);
Where src_Iamge and dst_Image is the source and destination image correspondingly and pixel[i] is the selected pixel i wanted to draw in the dst image. I have include the real out image below.
have an source Ipl image, I want to copy some of the part of the image to a new destination image pixel by pixel. can any body tell me how can do it? I use c,c++ in opencv. For example if the below image is source image,
The real output image
EDIT:
I can see the comments suggesting cvGet2d. I think, if you just want to show "points", it is best to show them with a small neighbourhood so they can be seen where they are. For that you can draw white filled circles with origins at (x,y), on a mask, then you do the copyTo.
using namespace cv;
Mat m(input_iplimage);
Mat mask=Mat::zeros(m.size(), CV_8UC1);
p1 = Point(x,y);
r = 3;
circle(mask,p1,r, 1); // draws the circle around your point.
floodFill(mask, p1, 1); // fills the circle.
//p2, p3, ...
Mat output = Mat::zeros(m.size(),m.type()); // output starts with a black background.
m.copyTo(output, mask); // copies the selected parts of m to output
OLD post:
Create a mask and copy those pixels:
#include<opencv2/opencv.hpp>
using namespace cv;
Mat m(input_iplimage);
Mat mask=Mat::zeros(m.size(), CV_8UC1); // set mask 1 for every pixel you wanna copy.
Rect roi=Rect(x,y,width,height); // create a rectangle
mask(roi) = 1; // set it to 0.
roi = Rect(x2,y2,w2,h2);
mask(roi)=1; // set the second rectangular area for copying...
Mat output = 100*Mat::ones(m.size(),m.type()); // output with a gray background.
m.copyTo(output, mask); // copy selected areas of m to output
Alternatively you can copy Rect-by-Rect:
Mat m(input_iplimage);
Mat output = 100*Mat::ones(m.size(),m.type()); // output with a gray background.
Rect roi=Rect(x,y,width,height);
Mat m_temp, out_temp;
m_temp=m(roi);
out_temp = output(roi);
m_temp.copyTo(out_temp);
roi=Rect(x2,y2,w2,h2);
Mat m_temp, out_temp;
m_temp=m(roi);
out_temp = output(roi);
m_temp.copyTo(out_temp);
The answer to your question only requires to have look at the OpenCV documentation or just to search in your favourite search engine.
Here you've an answer for Ipl images and for newer Mat data.
For having an output as I see in your images, I'd do it setting ROI's, it's more efficient.
I have successfully detected a face out of an image having other things in background using OpenCv.
Now I need to extract just the detected part (i.e. face) and convert it into some image format like jpeg or gif to make a face database to use for my neural net training.
How can I do this?
Once you detect the faces, you get opposite corners of a rectangle, which is used to draw rectangles around the face.
Now you can set image ROI ( Region of Interest) , crop the ROI and save it as another image.
/* After detecting the rectangle points, Do as follows */
/* sets the Region of Interest
Note that the rectangle area has to be __INSIDE__ the image */
cvSetImageROI(img1, cvRect(10, 15, 150, 250));
/* create destination image
Note that cvGetSize will return the width and the height of ROI */
IplImage *img2 = cvCreateImage(cvGetSize(img1),
img1->depth,
img1->nChannels);
/* copy subimage */
cvCopy(img1, img2, NULL);
/* always reset the Region of Interest */
cvResetImageROI(img1);
Above code is taken from http://nashruddin.com/OpenCV_Region_of_Interest_(ROI)
Further cvSaveImage function can be used to save image to a file.
try this:
for(i=0;i<(pFaceRectSeq?pFaceRectSeq->total:0);i++)
{
CvRect* r=(CvRect*)cvGetSeqElem(pFaceRectSeq,i);
int width=r->width;
int height=r->height;
cvSetImageROI(pInpImg,*r);
IplImage* pCropImg=cvCreateImage(cvSize(width,height),IPL_DEPTH_8U,3);
cvCopy(pInpImg,pCropImg,NULL);
cvShowImage("Cropped Window",pCropImg);
cvWaitKey(0);
cvResetImageROI(pInpImg);
cvReleaseImage(&pCropImg);
}