Newbie: Require assistance - modify existing jpeg image ,save and display on LCD

[dbugger]

Hi

I have to develop a feature in my application which enables modifying an jpeg image and saving it.

This feature is launched from one of the existing screens in my project

Let me divide this task
1. Open an existing jpeg image. This should be displayed on LCD (640x480)
2. Modify the jpeg image using stylus (Touch Screen is integrated)
3. Save the modified image

What are the steps involved? How should I proceed?

-Thanks in advance

[wysota]

Take a look at QImage.

[dbugger]

Thanks for your response.

I have tried using the QImage
I open the jpeg file using Qimage. But the image is not visible on the LCD.
What else should I do? I tried using QImageIO to display the image on LCD. But, after opening, the old screen itself is displayed on LCD. How do I make this image to display on the LCD?
This is what I have done:
QImage image;
const char *buffer = "/root/ferrari.jpg";
image.load(buffer);

[wysota]

You have to display the image somewhere. QImage only holds the data. You can use QLabel to display a QPixmap that you can obtain from QImage or directly load from file.

[dbugger]

Thanks pal!

This is what I have done. But, I still dont see the image on the LCD. The screen is not refreshing. Have I missed something here?
This is what I have done-

QImage image;
const char *buffer = "/root/ferrai";
image.load(buffer);
 
QPixmap pix;
pix.fromImage(image, 0);
 
QLabel labl;
labl.setPixmap(pix);

QImage image;
const char *buffer = "/root/ferrai";
image.load(buffer);

QPixmap pix;
pix.fromImage(image, 0);

QLabel labl;
labl.setPixmap(pix);

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[jacek]

QPixmap pix;
pix.fromImage(image, 0);

QPixmap::fromImage() is a static method --- it won't change the "pix" variable, but instead it returns a new QPixmap.

[wysota]

And the label probably goes out of scope.

[dbugger]

Thanks for your response

What are you hinting at? Do you mean that that the image I want to display is not available in QLabel? If that is the case how can I achieve it?

I see 2 other classes QImageIO and QIODevice. As, I have to display the image on LCD (touhscreen integrated) which is an IO device, should one of these classses be also used?

[jpn]

1) QPixmap::fromImage() is a static method --- it won't change the "pix" variable, but instead it returns a new QPixmap.

QPixmap pixmap = QPixmap::fromImage(image);

QPixmap pixmap = QPixmap::fromImage(image);

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2) And the label probably goes out of scope.

{
    QLabel label;
    label.setPixmap(pixmap);
    label.show();
} // label is a local variable and goes out of scope, so gets destructed according to normal C++ rules

{
    QLabel label;
    label.setPixmap(pixmap);
    label.show();
} // label is a local variable and goes out of scope, so gets destructed according to normal C++ rules

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VS.

{
    QLabel* label = new QLabel;
    // label->setAttribute(Qt::WA_DeleteOnClose); // hint
    label->setPixmap(pixmap);
    label->show();
} // the pointer variable goes out of scope but the object itself remains alive

{
    QLabel* label = new QLabel;
    // label->setAttribute(Qt::WA_DeleteOnClose); // hint
    label->setPixmap(pixmap);
    label->show();
} // the pointer variable goes out of scope but the object itself remains alive

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[dbugger]

Thanks.

I will try and let you know

Cheers

[dbugger]

I tried your suggestion. There is no change in the screen that is displayed on the LCD. But, if I press one of the buttons (which is on the keypad), the current screen vanishes but I still dont see the desired image on LCD. Though on close observation, on the top right corner of the LCD, I see something, but it is not part of the image that I want to display
Where am I going wrong?

Thanks for your patience

[wysota]

Could we see a larger snippet of code?

[dbugger]

This is what I have done:

QImage image;
const char *buffer = "/root/whitescreen.jpg";
image.load(buffer);
QPixmap pix;
pix.fromImage(image, 0);
QLabel* label = new QLabel;
label->setPixmap(pix);
label->show();

QImage image;
const char *buffer = "/root/whitescreen.jpg";
image.load(buffer);
QPixmap pix;
pix.fromImage(image, 0);
QLabel* label = new QLabel;
label->setPixmap(pix);
label->show();

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Please excuse me for my mistakes if any

[jpn]

You are still using QPixmap::fromImage() incorrectly.

[wysota]

And this snippet is not larger than the previous one. Could we see in what exact context is the code situated? Is it in main() or is it a method of some class and where is it called?

[dbugger]

This is where the code sits

void class_name::function()
{
    #if PRINT_DEBUG
            qDebug("%s : xxxxxxxxx yyyyyyy Pressed",pname);
    #endif
 
    #if 1
         printf("\nentering open image\n");
         openimage();//ING_IND
         printf("\nexited open image\n");
     #endif
}
 
 
void class_name::openimage()
{
      closecurrentscreen();
/*open jpeg image*/
      QImage image;
      const char *buffer = "/root/whitescreen.jpg";
      QPixmap pix;
      pix.load(buffer);
      QLabel* label = new QLabel;
      label->setPixmap(pix);
      label->show(); 
/*modify image*/
                 /*need to code*/
/*save image*/
                 /*need to code*/
}

void class_name::function()
{
    #if PRINT_DEBUG
            qDebug("%s : xxxxxxxxx yyyyyyy Pressed",pname);
    #endif

    #if 1
         printf("\nentering open image\n");
         openimage();//ING_IND
         printf("\nexited open image\n");
     #endif
}


void class_name::openimage()
{
      closecurrentscreen();
/*open jpeg image*/
      QImage image;
      const char *buffer = "/root/whitescreen.jpg";
      QPixmap pix;
      pix.load(buffer);
      QLabel* label = new QLabel;
      label->setPixmap(pix);
      label->show(); 
/*modify image*/
                 /*need to code*/
/*save image*/
                 /*need to code*/
}

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This is exactly what I intend to do. Before opening the image,
- close the current screen
- open the image
- modify
- save

But even the current screen itself is not getting closed.

Thanks pal for everything!!

[dbugger]

I would like to show some more of the code but it is confidential

[dbugger]

but I can give you the scenario if you want to know. but that I cannot write in the forum, I can write you a private message, if that is fine with you!!

Thanks!!

[wysota]

You will surely have to redesign your code. Qt is event driven. That means that the code is not structured as a single scenario flow, but instead it's a state machine that reacts on events received. Your method will have to display the image and do nothing more with it. Other methods will perform actions associated with editing the image and finally yet another one will save it back.

My guess is that your slot is not called at all, so verify that first by inserting some debug statements in it.

[dbugger]

Do you mean to say that the control isn't entering the "openimage" function? If that is the case, I can see the debug messages, which means that my SLOT is fine. But I am not sure as to how to make my current application which has many screens to go inactive/ionvisible and display the jpeg image on LCD.
Should/Can we modify the frame buffer?