How to output Debug to Status Bar?

[Marxsta3]

Thanks @Pl45m4 - I'm now trying to do two things at once.
Return the RGB value of a pixel point and it's XY coordinate.
This compiles but receiving the message:

QImage::pixel: coordinate (207,201) out of range.
Any thoughts on the structure of the code?

void ImageViewer::mouseMoveEvent(QMouseEvent *event)
{
    QString rgbValue;
    QPointF mousePosition = event->pos();
    rgbValue = QPixmap().toImage().pixel(mousePosition.x(), mousePosition.y());
    QDebug(&rgbValue) << event->pos();
    statusBar()->showMessage(rgbValue);
}

[JonB]

@Marxsta3
Just read the message and look at your code (nothing wrong with its "structure"). This can presumably only mean that the position, (207,201) is out of the bounds of QPixmap().toImage().

Which is hardly surprising, since QPixmap() is an empty QPixmap! If you want to look at mouse position on some pixmap you have, then look at that pixmap!

[Pl45m4]

@Marxsta3 said in How to output Debug to Status Bar?:

QImage::pixel: coordinate (207,201) out of range.
Any thoughts on the structure of the code?

Fill your Pixmap with data, like

void ImageViewer::mouseMoveEvent(QMouseEvent *event)
{
    QString rgbValue;
    QPointF mousePosition = event->pos();
    QPixmap pix(200, 200); // set some size
    pix.fill(Qt::blue);
    rgbValue = pix.toImage().pixel(mousePosition.x(), mousePosition.y());
    QDebug(&rgbValue) << event->pos();
    statusBar()->showMessage(rgbValue);
}

Also, you need to show it somewhere in order to get the actual sync'ed pixel value. Then you don't have to deal with "out of bound" issues since you are only moving on your image
Currently you are moving your mouse over an empty window while checking this specific mouse position in your image or am I missing something?

[Marxsta3]

Tried a few changes and still get the out of range notification.
Will continue testing.

Reading:
https://www.qtcentre.org/threads/40754-Grab-the-color-of-a-pixel-of-the-screen

[JonB]

@Marxsta3
For your code to make any sense/be useful you must have some QPixmap somewhere outside of mouseMoveEvent which the mouse is moving over and for which you want to look at a pixel. No point you creating a pixmap in this method presumably. Just use whichever existing pixmap the mouse is moving over here, nothing to "try" or "test".

[Marxsta3]

Thanks @JonB takes me a while to comprehend as I'm new to it. Would you have an example code while I figure it out for myself?

[JonB]

@Marxsta3
But there isn't any example code because we don't know what you have got!

Can you please stop writing code/testing stuff and just think/describe what it is you want? You have said that you want to be inside mouseMoveEvent() and show a message about what pixel is at a certain point on a pixelmap image. Right? So that must mean you have some pixmap already that you are moving the mouse over, right? Otherwise why would you want to do what you are doing? So where is this QPixmap which you already have and are moving the mouse over? I don't know, only you do.

[Marxsta3]

@JonB i've got an app that loads a bmp, jpg or tiff in a window. The pixmap must be used to load the image into the window. I can see it used several times. What I would like to do is load an image and then with mouse pressed down (or hovering) over the image it detects the RGB values for each pixel. I'm wanting to extract a few bits of info. The XY coordinate of the mouse, the rgb values of the pixel at that point, then later I want to adapt it to choose to allow either an rgb or cmyk image. The final status bar readings will be 1) XY coord 2) RGB (or CMYK) pixel value 3) The grey value at that point. I hope it's clearer now

[JonB]

@Marxsta3
So whatever variable you have your pixmap already loaded into for showing, and you are moving your mouse over, is the one you want to call pix.toImage() on in mouseMoveEvent(). That's all there is to say and should make sense.

[Pl45m4]

@Marxsta3 said in How to output Debug to Status Bar?:

The final status bar readings will be 1) XY coord 2) RGB (or CMYK) pixel value 3) The grey value at that point. I hope it's clearer now

So basically like OpenCV's namedWindow with an image?
At least the Linux version shows RGB pixel values and X / Y coordinate in some status bar.

You could also consider to change your design for that.
Make an image class based on QLabel, let's call it "ImageLabel"

• re-implement mouseMoveEvent, like you did in your QMainWindow class before.
• enable mouseTracking
• add a signal to show it in ImageViewer's status bar and pass everything else you need with it (position, pixel in RGB, grayscale value)

Btw: QImage doesn't support the CMYK color model. QImage is mostly RGB(A), (A)RGB or BGR
Check the formats here.

[Pl45m4]

[Marxsta3]

Oh my word @Pl45m4 that is precisely it. Would you be able to share the source code? Did you have to use OpenCV?

[Pl45m4]

@Pl45m4 said in How to output Debug to Status Bar?:

Make an image class based on QLabel, let's call it "ImageLabel"

• re-implement mouseMoveEvent, like you did in your QMainWindow class before.
• enable mouseTracking
• add a signal to show it in ImageViewer's status bar and pass everything else you need with it (position, pixel in RGB, grayscale value)

@Marxsta3 It's "just" this :)

Header

#ifndef IMAGELABEL_H
#define IMAGELABEL_H

#include <QLabel>
#include <QMouseEvent>


class ImageLabel : public QLabel
{
    Q_OBJECT

public:
    ImageLabel(QWidget *parent=nullptr);

protected:
    void mouseMoveEvent(QMouseEvent* ev) override;
    void leaveEvent(QEvent*ev) override;


signals:
    void mouseOverImage(QPoint px, int r, int g, int b, int gray);

};

#endif // IMAGELABEL_H

code file

#include "imagelabel.h"
#include <QRgb>
#include <QImage>

ImageLabel::ImageLabel(QWidget* parent):QLabel(parent)
{
    setMouseTracking(true);
    setScaledContents(true);
}

void ImageLabel::mouseMoveEvent(QMouseEvent *ev)
{

    if(pixmap() == nullptr)
    {
        QLabel::mouseMoveEvent(ev);
        return;
    }
    QPoint px = ev->pos();

    QRgb rgb = pixmap()->scaled(this->width(), this->height()).toImage().pixel(px.x(), px.y());
    int grayVal = qGray(rgb);
    emit mouseOverImage(ev->pos(), qRed(rgb), qGreen(rgb), qBlue(rgb), grayVal);

    QLabel::mouseMoveEvent(ev);
}

void ImageLabel::leaveEvent(QEvent *ev)
{
    // mouse left ImageLabel
    // -> trigger reset on statusBar
    emit mouseOverImage(QPoint(), 0, 0, 0, 0);
    QLabel::leaveEvent(ev);
}

And in your ImageViewer...
The string formatting is a mess, but you get the point ;)

ImageLabel * imgLbl = new ImageLabel(this);

connect(imgLbl, &ImageLabel::mouseOverImage, [this](QPoint p, int r, int g, int b, int gray){

        QString msg = "( " + QString::number(p.x()) + " / " + QString::number(p.y()) + " )" +
                "\t\t\tR: " +  QString::number(r) +
                "\tG: " + QString::number(g) +
                  "\tB: " + QString::number(b) +
                "\t\t\tGRAY: " + QString::number(gray);
        // reset statusBar if mouse left the image
        if(p == QPoint())
            statusBar()->clearMessage();
        else
            statusBar()->showMessage(msg);


    });

    QPixmap pix("Path/to/Image.jpg");

    imgLbl->setPixmap(pix);

    setCentralWidget(imgLbl);

@Marxsta3 said in How to output Debug to Status Bar?:

Did you have to use OpenCV?

No, I said, it's like OpenCV's window
Have a look here

• https://stackoverflow.com/questions/68405635/zooming-functionality-in-opencv-imshow-in-ubuntu

This is the default window to show images using OpenCV on Ubuntu. There you can see the coordinates and RGB values from where the cursor is.

[Marxsta3]

Great Pl45m4, it works.

Thank you everyone for your input.