I've been trying to print out a whole folder of images as the first stage of a project and haven't been able to get it working. The images are named "batch_X.jpg" (but the file type can change if something works better) and for testing I've been just having it print to pdf, to not waste thousands of pieces of paper. I can get the loop to go to completion and make files named "testX" to an output folder, however instead of them being the image I want to print, they always just show up as blank white pages.
Here is the code as I have been running it, complete with lines commented out all over the place
QApplication app(int argc, char** argv());
for (int q = 1; q <= 11; q++)
{
//int q = 4;
QString fileName=QStringLiteral("/Users/user/Desktop/imageTests/output/batch_%1.jpg").arg(q);
// QPrinter printer;
//QPrintDialog *dlg = new QPrintDialog(&printer,0);
//if(dlg->exec() == QDialog::Accepted) {
QPrinter printer(QPrinter::ScreenResolution);
printer.setResolution(3000);
//printer.setPageLayout(page_layout);
printer.setCopyCount(1);
printer.setDoubleSidedPrinting(false);
printer.setDuplex(QPrinter::DuplexNone);
printer.setColorMode(QPrinter::Color);
printer.setPageSize(QPrinter::Letter);
printer.setPaperSize(QPrinter::Letter);
printer.setPaperSource(QPrinter::Auto);
//printer.setCreator("Inkjet Plumber");
printer.setOrientation(QPrinter::Portrait);
printer.setPageMargins(0.0, 0.0, 0.0, 0.0, QPrinter::Inch);
//printer.setPageLayout(page_layout);
QString outputFileName = QStringLiteral("/Users/user/Desktop/testing/test%1.pdf").arg(q);
printer.setOutputFileName(outputFileName);
printer.setOutputFormat(QPrinter::PdfFormat);
QImage img(fileName);
QPainter painter(&printer);
painter.drawImage(QPoint(0,0),img);
painter.end();
//QMessageBox::information(this, tr("Title"), QString(fileName));
}
Your code looks correct.
It works on my side.
The only thing I would fix is resolution:
printer.setResolution(300);
Related
I'm trying to print multiple table (qtablewidget) objects in single pdf using qt.
I can print one table, using the code provided in(https://forum.qt.io/topic/80501/qpainter-howto-draw-table/7)
QPixmap pix(widget->size());
QPainter painter(&pix);
widget->render(&painter);
painter.end();
QPrinter printer(QPrinter::HighResolution);
printer.setOrientation(QPrinter::Landscape);
printer.setOutputFormat(QPrinter::PdfFormat);
printer.setPaperSize(QPrinter::A4);
printer.setOutputFileName("test.pdf"); // will be in build folder
painter.begin(&printer);
painter.drawPixmap(0, 0, pix);
painter.end();
However, if I try to print multiple tables, the code fails. If I create multiple QPainters, qt just outputs multiple pdfs, with one table in each pdf. I'm trying to do it using one QPainter and multiple QPixmaps, but no success so far.
Would anyone please let me know how I can get around it?
Any help would be appreciated
Regards,
How does the code fail? The below should work (I didn't test it). Note the absence of manual object lifetime management: let the compiler do it for you. A QPainter is a proper C++ class and knows how to release its resources without having to manually invoke QPainter::end().
void printWidgets(QWidgetList widgets) {
QVector<QPixmap> pixmaps;
for (auto *w : widgets) {
QPixmap pix(w->size());
QPainter painter(pix);
w->render(&painter);
pixmaps.push_back(pix);
}
QPrinter printer(QPrinter::HighResolution);
printer.setOrientation(QPrinter::Landscape);
printer.setOutputFormat(QPrinter::PdfFormat);
printer.setPaperSize(QPrinter::A4);
printer.setOutputFileName("test.pdf"); // will be in build folder
QPainter painter(&printer);
QPoint pos;
for (auto &pix : qAsConst(pixmaps)) {
painter.drawPixmap(pos, pix);
pos.ry() += pix.height(); // stack the output vertically
}
}
I have a big image of 7589x5537 that I put in a scene as a QPixmapGraphicsItem.
If I scale the QGraphicsView to 14.2318 and rotate it -35 degrees, the render of the pixmap starts behaving weirdly; tearing or completely disappearing.
This happens also at other rotations and scales, but only if they are big scaling of more than 14.
I've read about X11 limitations but I'm on Windows.
I'm on Qt 5.5
I've tested changing the content of the image to a bucketfill of tree pattern, exactly the same behaviour. The image is indexed, but with a RGB I have the same issue.
Anybody has a clue why this happens and how to fix it? Is the problem reproducible?
The issue seems to be related to the maximum value of unsigned int, dimension independent if not rotated. Creating an untilted image of 1 million by 200 pixels, one can zoom up to 4384x. In my computer the size of unsigned int is 4 bytes, which can handle roughly values up to 4000 million.
I presume Qt doesn't crop the upscaled image to the view before scaling it, or something similar. It is weird, thought, that it tears it instead of crashing exhausting resources, failing to allocate contiguous memory or something else.
Those are suspicions since at the moment I don't know how QGraphicsView implements scaling.
#include <QtWidgets>
int main(int argc, char *argv[]) {
QApplication a(argc, argv);
unsigned int w = 7589;
unsigned int h = 5537;
QImage image(w, h, QImage::Format_ARGB32);
for(unsigned int j = 0; j < h; j++)
{
for(unsigned int i = 0; i < w; i++)
{
QRgb rgb = qRgb(i%255,j%255,(i+j)%255);
image.setPixel(i, j, rgb);
}
}
QPixmap imagepm = QPixmap::fromImage(image);
QGraphicsPixmapItem* item = new QGraphicsPixmapItem(imagepm);
item->setTransformationMode(Qt::FastTransformation);
QGraphicsScene* scene = new QGraphicsScene;
scene->addItem(item);
QGraphicsView* view = new QGraphicsView(scene);
view->rotate(-35);
view->scale(14.2318,14.2318);
view->show();
return a.exec();
}
The fix requires cutting the image up into tiles, grouping them under a single parent item, and then proceeding as you did before. The tiles would be an implementation detail that you don't need to worry about.
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
I have an RGB888 format qImage defined as follows:
myQrgb = QImage(img_in, width, height, QImage::Format_RGB888);
I wish to alter specific pixel values, so I followed the example here, like so:
QRgb value = qRgb(0, 0, 0);
myQrgb.setPixel(i, j, value);
This, however, always produces a segmentation fault regardless of the values of i and j (e.g. i = j = 2).
I am guessing it is because I am incorrectly using QRgb to manipulate pixels in a QImage::Format_RGB888. What should I do instead?
I think the problem may be more related to the img_in data with which you are initializing the image. Are you sure that data is valid?
The following example successfully paints a white square with a black square in the corner.
#include <QtGui>
int main(int argc, char **argv) {
QApplication app(argc, argv);
QImage img(100, 100, QImage::Format_RGB888);
img.fill(QColor(Qt::white).rgb());
for (int x = 0; x < 10; ++x) {
for (int y = 0; y < 10; ++y) {
img.setPixel(x, y, qRgb(0, 0, 0));
}
}
QLabel l;
l.setPixmap(QPixmap::fromImage(img));
l.show();
return app.exec();
}
There are few things you need to confirm:
According to QImage constructor you're using, make sure img_in remains valid throughout the life span of QImage object. By the way, QImage destructor will not delete your data (img_in).
If the pixel position you're setting is not valid coordinate, setPixel()'s behavior is undefined.
I suspect the first case, img_in is probably vanishing from QImage. You may want to try to create a QImage using other constructor like QImage(10, 10, QImage::Format_RGB888) and play with setPixel().
I have a problem which I have been trying to figure out for few days now. I am using OpenCV to get frames from a camera and then I am converting it to QImage and trying to save the frame on a disk. The problem I am facing is that if I compile/run the code in release/debug mode in visual studio then it works fine. If I run the executable created by visual studio for debug mode then it runs fine. But if I run the executable created by visual studio in release mode, the gui works well except that the QImage save() function doesn't work anymore. If I use OpenCV function for saving the frame then it works well in all modes. The QImage that I am trying to save is notNull because my comments text box displays the line I print inside but the save function returns false. I would really appreciate help.
Here is a little code:
Code for conversion between IplImage and QImage (I have also used another code, with the same result)
QImage A::IplImage2QImage(const IplImage *iplImage)
{
int height = iplImage->height;
int width = iplImage->width;
if (iplImage->depth == IPL_DEPTH_8U && iplImage->nChannels == 3) {
const uchar *qImageBuffer = (const uchar*)iplImage->imageData;
QImage img(qImageBuffer, width, height, QImage::Format_RGB888);
return img.rgbSwapped();
}
else {
// qWarning() << "Image cannot be converted.";
return QImage();
}
}
void A::getFrame()
{
commentsTextBox->setText("getFrame");
if (VI.isFrameNew(device1)) {
VI.getPixels(device1, (unsigned char *)frame->imageData, false, true);
}
QImage qimg2 = IplImage2QImage(frame);
m_Label->setPixmap(QPixmap::fromImage(qimg2));
if (!qimg2.isNull()) {
x = qimg2.save("C:\\Data\\test.jpg");
commentsTextBox->append("notEmpty33");
}
}
I had the same problem to QImage::load(). I will post a copy of the solution pointed out in the link of alexisdm, in order to make it clearer.
Under windows the qjpeg4.dll must in a imageformats directory under
the application's directory by default.
Thank you!
Try something like this,
// Prepare the url,
QUrl url("file:///home/ubuntu/Desktop/image.jpg");
// Get the path,
QString path = url.path();
// Save the image,
myQimage.save(path);