I have an application where I copy some raw image data into a QImage directly:
QImage* img = new QImage(desc.Width, desc.Height, QImage::Format_RGB32);
for (y = 0; y < img->height(); y++)
{
memcpy(img->scanLine(y), &rawData[y * pRes->RowPitch], pRes->RowPitch);
}
return img;
Later this QImage is drawn via a call
painter.drawPixmap();
Unfortunately drawPixmap() cannot handle a QImage directly, so it first has to be converted:
m_bgImage = new QPixmap();
m_bgImage->convertFromImage(image);
Due to timing reasons I would like to drop this additional conversion step.
Thus my question: are there any function in QPixmap that allow direct image data manipulation right as in QImage?
My idea would be to start with a QPixmap from the very beginning, copy the raw image data into the QPixmap object and then use it directly.
Thanks :-)
First of all you won't need that loop to create the QImage. You can:
QImage* img = new QImage(&rawData, desc.Width, desc.Height, pRes->RowPitch * 4, QImage::Format_RGB32);
Then you can
painter.drawImage(QPointF(0,0),*img);
If there is any specific reason to use QPixmap (like QPixmap caching) you will have no other choice than convert it to QPixmap first.
Related
I have created a simple application and I need export from pixmap to the 16-bit bmp image. I have several pixmap items so I have the for loop like this where I first create QImage and convert it to Format_RGB16:
for(QList<image_handler * >::iterator it=imageItems->begin(); it!=imageItems->end(); it++)
{
...
// image_handler inherits QPixmap
QFile export_image(path+"/img_"+code+".bmp");
QImage export_img = (*it)->toImage().convertToFormat(QImage::Format_RGB16);
export_img.save(&export_image, "BMP");
...
}
where image_handler is my custom QPixmap. Images are exported at path given, with correct filename. However when I look at properties of file (in windows) I can see that image depth is 24-bit. Unfortunately I need them to be 16-bit.
What I am doing wrong here? Or is this a bug in Qt? Then how can I export 16-bit bmps from pixmap?
Turns out, that Qt forcibly converts image, before saving it to bmp.
qt-src/src/gui/image/qbmphandler.cpp:777:
bool QBmpHandler::write(const QImage &img)
{
QImage image;
switch (img.format()) {
case QImage::Format_ARGB8565_Premultiplied:
case QImage::Format_ARGB8555_Premultiplied:
case QImage::Format_ARGB6666_Premultiplied:
case QImage::Format_ARGB4444_Premultiplied:
image = img.convertToFormat(QImage::Format_ARGB32);
break;
case QImage::Format_RGB16:
case QImage::Format_RGB888:
case QImage::Format_RGB666:
case QImage::Format_RGB555:
case QImage::Format_RGB444:
image = img.convertToFormat(QImage::Format_RGB32);
break;
default:
image = img;
}
...
So, if you need to save bmp 16bit, you'll have to do it manually, filling header and using QImage::bits() and QImage::byteCount().
Some background info about my issue. My goal is to optimize drawing of images coming from webcam, the images come as QVideoFrame and are currently loaded in to QImage and drawn from there. This solution works fine, but drawing QImage is very slow on X11. Drawing one image takes about 20ms which doesn't sound like much but when you do this for every frame this cut's the framerate of the camerafeed to half.
I did some research and testing, drawing QPixMaps in X11 can be done about 10 times faster than drawing QImages.
This is how the drawing process is done currently
if(mVFcurrentFrame.map(QAbstractVideoBuffer::ReadOnly))
{
QImage image(mVFcurrentFrame.bits(), mVFcurrentFrame.width(), mVFcurrentFrame.height(), mVFcurrentFrame.bytesPerLine(), imageFormat);
painter->drawImage(0,0,image); //Takes about 20ms
mVFcurrentFrame.unmap();
}
What i have tried so far:
Converting the QImage to QPixMap, this works but the conversion is as slow as painting the Qimage
Loading the QVideoFrame straight to QPixMap with QPixMap::loadFromData(), can't make it work.
So my question is, can i convert QVideoFrame straight to QPixMap and draw it instead of using QImage and how would you do the QVideoFrame to QPixmap conversion without using QImage in between?
I have tried using QPixMap::loadFromData() method to load the video frame but so far i have been unable to make it work.
If this isn't possible could i thread the QImage to QPixMap conversion or optimize the drawing in some other way?
This is my problem too.
camera frames are shown very slowly in QLabel.
my code is here:
QCamera *camera = new QCamera(this);
camera->setCaptureMode(QCamera::CaptureViewfinder);
QVideoProbe *videoProbe = new QVideoProbe(this);
bool ret = videoProbe->setSource(camera);
if (ret) {
connect(videoProbe, SIGNAL(videoFrameProbed(const QVideoFrame &)),
this, SLOT(present(const QVideoFrame &)));
}
camera->start();
...
...
bool MainWindow::present(const QVideoFrame &frame)
{
QVideoFrame cloneFrame(frame);
if(cloneFrame.map(QAbstractVideoBuffer::ReadOnly))
{
QImage img(
cloneFrame.size(), QImage::Format_ARGB32);
qt_convert_NV21_to_ARGB32(cloneFrame.bits(),
(quint32 *)img.bits(),
cloneFrame.width(),
cloneFrame.height());
label->setPixmap(QPixmap::fromImage(img));
cloneFrame.unmap();
}
return true;
}
Is there a way to pass an image as a name not as a path to Qpixmap in QT(C++),, for example i have the following code in which the processed image should be displayed using Qpixmap label but when i tried that i have to save it and then to pass it to Qpixmap to be displayed,,, but it's not an efficient way so could anybody help me please i'm new to Qt and have no experience..
void MainWindow::on_pushButton_3_clicked()
{
cv::Mat hsv_img, seg_img,infected_area, hsv_infected,seg_input,hsv_seg;
Mat filter_img,hsv;
cv::Mat input_image = imread(this->file_name.toAscii().data());
medianBlur(input_image,filter_img,7);
cvtColor(filter_img, hsv, CV_BGR2HSV);
hsvSeg(filter_img,hsv, hsv_img, seg_img,14.0,0.0,117.0,255.0,133.0,179.0);//call hsv segmentation function to segment leaf
cvtColor(seg_img, hsv_seg, CV_BGR2HSV);
hsvSeg(seg_img,hsv_seg, hsv_infected, infected_area,0.09*255,0.01*255,0.1*255,0.14*255,1.0*255,1.0*255);//call hsv segmentation to segment infected areas
imwrite( "C:/Image.jpg", filter_img );
this->ui->ImageView_2->setPixmap(QPixmap("C:/Image.jpg"));// here the problem
Try this:
cvtColor(mat, mat, CV_BGR2RGB);
QImage qimg((uchar*)mat.data, mat.cols, mat.rows, mat.step, QImage::Format_RGB888);
ui->label->setPixmap(QPixmap::fromImage(qimg));
I'm new to graphics programming (pixels, images, etc..)
I'm trying to convert Raw data to QImage and display it on QLabel. The problem is that, the raw data can be any data (it's not actually image raw data, it's binary file.)
The reason if this is that, to understand deeply how pixels and things like that work, I know I'll get random image with weird results, but it will work.
I'm doing something like this, but I think I'm doing it wrong!
QImage *img = new QImage(640, 480, QImage::Format_RGB16); //640,480 size picture.
//here I'm trying to fill newly created QImage with random pixels and display it.
for(int i = 0; i < 640; i++)
{
for(int u = 0; u < 480; u++)
{
img->setPixel(i, u, rawData[i]);
}
}
ui->label->setPixmap(QPixmap::fromImage(*img));
am I doing it correctly? By the way, can you point me where should I learn these things? Thank you!
Overall it's correct. QImage is a class that allows to manipulate its own data directly, but you should use correct pixel format.
A bit more efficient example:
QImage* img = new QImage(640, 480, QImage::Format_RGB16);
for (int y = 0; y < img->height(); y++)
{
memcpy(img->scanLine(y), rawData[y], img->bytesPerLine());
}
Where rawData is a two-dimension array.
This is how I saved a raw BGRA frame to the disk:
QImage image((const unsigned char*)pixels, width, height, QImage::Format_RGB32);
image.save("out.jpg");
Syntactically, your code appears to be correct.
Reading the class signature, you may want to call setPixel in the following manner:
img->setPixel(i, u, QRbg(##FFRRGGBB));
Where ##FFRRGGBB is a color quadruplet, unless, of course, you want monochrome 8 bit support.
Additionally, declaring a naked pointer is dangerous. The following code is equivalent:
QImage image(640, 480, QImage::Format_something);
QPixmap::fromImage(image);
And will deallocate appropriately upon function completion.
Qt Examples directory is a great place to search for functionality. Also, peruse the class documentation because they're littered with examples.
I've found very similiar topic: how to convert an opencv cv::Mat to qimage , but it does not solve my problem.
I have function converting cv::Mat to QImage
QImage cvMatToQImg(cv::Mat& mat)
{
cv::Mat rgb;
if(mat.channels()==1)
{
cv::cvtColor(mat,rgb,CV_GRAY2BGR);
cv::cvtColor(rgb,rgb,CV_BGR2BGRA);
QImage temp = QImage((unsigned char*)(rgb.data), rgb.cols,
rgb.rows,QImage::Format_ARGB32 );
QImage returnImage = temp.copy();
return returnImage;
}
And it's works for my but I want to make it more efficient.
First: why changing 2 cvtColor functions with:
cv::cvtColor(mat,rgb,CV_GRAY2BGRA)
fails on
QImage returnImage = temp.copy()
with segfault.
Then how to eliminate copying of QImage. When I simply return temp image, I'm getting segfault.
Any other optimalizations can be done there? It's very often used function so I want to make it as fast as possible.
Your solution to the problem is not efficient, in particular it is less efficient then the code I posted on the other question you link to.
Your problem is that you have to convert from grayscale to color, or RGBA. As soon as you need this conversation, naturally a copy of the data is needed.
My solution does the conversion between grayscale and color, as well as between cv::Mat and QImage at the same time. That's why it is the most efficient you can get.
In your solution, you first try to convert and then want to build QImage around OpenCV data directly to spare a second copy. But, the data you point to is temporary. As soon as you leave the function, the cv::Mat free's its associated memory and that's why it is not valid anymore also within the QImage. You could manually increase the reference counter of the cv::Mat beforehand, but that opens the door for a memory leak afterwards.
In the end, you attempt a dirty solution to a problem better solved in a clean fashion.
It may be easiest to roll your own solution. Below is the current OpenCV implementation for going from gray to RGBA format:
template<typename _Tp>
struct Gray2RGB
{
typedef _Tp channel_type;
Gray2RGB(int _dstcn) : dstcn(_dstcn) {}
void operator()(const _Tp* src, _Tp* dst, int n) const
{
if( dstcn == 3 )
for( int i = 0; i < n; i++, dst += 3 )
{
dst[0] = dst[1] = dst[2] = src[i];
}
else
{
_Tp alpha = ColorChannel<_Tp>::max();
for( int i = 0; i < n; i++, dst += 4 )
{
dst[0] = dst[1] = dst[2] = src[i];
dst[3] = alpha;
}
}
}
int dstcn;
};
Here is where the actual cvtColor call occurs:
case CV_GRAY2BGR: case CV_GRAY2BGRA:
if( dcn <= 0 ) dcn = 3;
CV_Assert( scn == 1 && (dcn == 3 || dcn == 4));
_dst.create(sz, CV_MAKETYPE(depth, dcn));
dst = _dst.getMat();
if( depth == CV_8U )
CvtColorLoop(src, dst, Gray2RGB<uchar>(dcn));
This code is contained in the color.cpp file in the imgproc library.
As you can see, since you are not setting the dstCn parameter in your cvtColor calls, it defaults to dcn = 3. To go straight from gray to BGRA, set dstCn to 4. Since OpenCV's default color order is BGR, you'll still need to swap the color channels for it to look right (assuming you get your image data from an OpenCV function). So, it may be worth it to implement your own converter possibly following the above example, or using ypnos answer here.
Also, have a look at my other answer involving how to integrate OpenCV with Qt.
The problem is that both the cv::Mat and QImage data isn't necessarily contiguous.
New data rows in opencv start on a 32bit boundary (not sure about QImage - I think it's system dependant) so you can't copy a memeory block unless your rows happen to be exact multiples of 4bytes
See How to output this 24 bit image in Qt