How to save images in a different format

kosai

Hi everyone!
my problem is that i am using 'save(const QString&, const char*)' function to save the image in another format but it doesn't work properly !
the difference between the original and the save image is obviouse but the extention still the same!!
i have a problem on my computer or i didn't understand what the 'save' function does??

SGaist

Hi and welcome to devnet,

What code are you using ?
What version of Qt are you using ?
What OS are you running ?
What compiler are you using ?
What image format do you have as input ?
What image format are you trying to have as output ?
What is the exact error you have ?
What output are you expecting ?
What output are you getting ?

kosai

i am programming in C++ language , Qt 4.11.1 , on Windows 7, i am using Qt 5.14.2 MinGW 64 bit, input format (png, jpg, jpeg, gif), just(jpeg) as output, i did not have error or either warning , images are being saved succecfully but its not changing the format !

jsulm

@kosai Please show your code

kosai

void Mwindow::NvlElem(void)
{
    QDir::setCurrent(m_ImgDir);//setting the Directory file
    if(!Line->text().isEmpty())
    {
        //if user write name of object
        //List->addItem(Line->text());
        List->addItem(Line->text());
        //**
        if(List->count() == 1)
            List->setCurrentRow(0);
        return;
    }

    //get Image
    QString ImgDir = QFileDialog::getOpenFileName(this,
                                                 "Ouvrir un fichier",
                                                 QString(),
                                                 "Images (*.png *.gif *.jpg *.jpeg)");
    //--Display Img on Tab
    ImgPixmap->load(ImgDir);
    ImgWin->setPixmap(*ImgPixmap);
    //--save Img in Items
    Image->load(ImgDir);
    QString ImgExt(ImgDir.right(4)), RImgName, ImgName;
    if(ImgExt[0] != ".")
        ImgExt = ImgDir.right(5);
    //get extention
    //--i did not find a better way to get extention !
    for (int i(ImgDir.length()); i >= 0; i--) {
        if(ImgDir[i] == "/")
            break;
        RImgName += ImgDir[i];
    }
    for(int i(RImgName.length()-1); i >= 0; i--) {
        if(RImgName[i] == ".")
            break;
        ImgName += RImgName[i];
    }
    //--here is the prblm !!!!
    if(Image->save(ImgName+ImgExt, "png"))
    {
        List->addItem(ImgName);
    }
    //*
    if(List->count() == 1)
        List->setCurrentRow(0);
//*****tring another way  using QImageWriter but it doesnt work either!
    ImgWriter->setFileName(ImgName);
    Line->setText(ImgWriter->fileName());
}

Christian Ehrlicher

The format is 'PNG', not 'png'.
The extension can be retrieved via QFileInfo and there is no need to create a QImage with new.

kosai

ok!
i tried "PNG" its the same problem !

jsulm

@kosai In your first post you wrote: "but the extention still the same". This is a different problem than "but its not changing the format". So, did you make sure the format was indeed not changed?

kosai

the problem is a little bit bizzard !
it's like changing bytes into the desired format --> if you put saved image with the original you will distinguish the diffrence !
but unlike if you go to the file on the desktop the extention doesn't change at all !!
i hope this helps to understand my problem?

jsulm

@kosai said in How to save images in a different format:

i hope this helps to understand my problem?

Not really.
What exactly is the problem:

Wrong file extension?
File is not stored as png?

Please be more clear.
If the file extension is not what you want then check your code and use @Christian-Ehrlicher suggested to get file extension.

J.Hilk

@kosai said in How to save images in a different format:

ile on the desktop the extention doesn't change at all !!

why should the extension change ? you extract it from the select file

QString ImgExt(ImgDir.right(4)), RImgName, ImgName;
    if(ImgExt[0] != ".")
        ImgExt = ImgDir.right(5);

and than append it again to the filename when you save it

Image->save(ImgName+ImgExt, "png")

without changing it in-between, of course it will have the same extension.

kosai

yeah! you are right i shouldn't put the original extention with the name !
thank you everyone !

SGaist

Another issue in your code, why are you forcing the output to be PNG and yet allow other extensions ? That does not really make sense. Personally I would be very surprised to find PNG while opening for example a .bmp file.