Grayscale image Color Conversion

painting a grayscale image into label

How do i use
QImage convertToFormat
& set color

I need to make whatever is black in the image and make it transparent
& whatever is white or partially white and make another color

Code:

---

while(x < secondaryImage.height()){
            while(y < secondaryImage.width()){
                if (secondaryImage.pixel(x,y) == 0)
                    secondaryImage.setPixel(x, y, Qt::red);
                y++;
            }
            x++;
        }

---

Thats what i got so far from other post
But its not working

If someone could please show me an example of how to go about doing it
or direct me accordingly

Kind Regards

I am not sure wether I understood your request the right way. I am assuming that you want to convert all black pixels to full transparency and all other pixels to red.
The first point is your loop which is not correctly initialized. Even if you initialized x and y outside the loop, latest when scanning the second column your variable y will be out of range, so the inner loop will be performed only once.

Your loop should look like

Code:

---

for ( x = 0; x < secondaryImage.width(); ++x )
{
    for ( y = 0; y < secondaryImage.height(); ++y )
    {
         if ( secondaryImage.pixel( x, y ) == Qt::black )
             secondaryImage.setPixel( x, y,  QColor( 0, 0, 0, 0 ));   // fully transparency, color doesn´t matter
         else
             secondaryImage.setPixel( x, y, Qt::red );
    }
}

---

I did not test the code!

Loop: Thanks that sorted the "out of scope problem"

Though the image editing.... Nothing happens
Any Ideas is there another way of changing colour

For the time being i'm inverting pixels of whole image until I get a more graphic appealing solution

can you show the whole code you are using?

The Inversion Color of image
Loading Image function

Code:

---

QFileDialog dialog2(this, "Upload secondary");
    dialog2.setNameFilter(tr("Images (*.png *.xpm *.jpg *.bmp)"));
    dialog2.setViewMode(QFileDialog::Detail);
 
    if(dialog2.exec())
    {
        imageFileName2 = dialog2.selectedFiles().first();
    }
 
    primaryImage.load(imageFileName1);
    primaryImage.invertPixels();

---

In paint Function:

Code:

---

painter.drawImage(QPoint(0, 0), secondaryImage);

---

The Changing color version of program ie(commented out until solution found)

Code:

---

for (int x = 0; x < secondaryImage.width(); ++x)
    {
        for (int y = 0; y < secondaryImage.height(); ++y)
        {
             if ( secondaryImage.pixel(x, y) == Qt::black)
                 secondaryImage.setPixel(x, y, QColor( 0, 0, 0, 0 )); //This line gives compiler error :confused:
             else
                  secondaryImage.setPixel( x, y, Qt::red ); //Nothing happens here :(
    }
    }

---

Ideas most welcome

sorry, my code is not correct. As the documentation stipulates, the last argument of setPixel() should be an uint!

Try wether next code do what you want.

Code:

---

QRgba transparentPixel, redPixel;
transparentPixel = QRgba( 0, 0, 0, 0 );                // fully transparency, color doesn´t matter
redPixel = QRgba( 255, 0, 0, 255 );                    // red, no transparency
 
for ( x = 0; x < secondaryImage.width(); ++x )
{
    for ( y = 0; y < secondaryImage.height(); ++y )
    {
         if ( secondaryImage.pixel( x, y ) == Qt::black )     // check wether working right!
             secondaryImage.setPixel( x, y, transparentPixel);   
         else
             secondaryImage.setPixel( x, y, redPixel );
    }
}

---

sorry, my code is not correct. As the documentation stipulates, the last argument of setPixel() should be an uint!

Try wether next code do what you want.

Code:

---

QRgba transparentPixel, redPixel;
transparentPixel = QRgba( 0, 0, 0, 0 );                // fully transparency, color doesn´t matter
redPixel = QRgba( 255, 0, 0, 255 );                    // red, no transparency
 
for ( x = 0; x < secondaryImage.width(); ++x )
{
    for ( y = 0; y < secondaryImage.height(); ++y )
    {
         if ( secondaryImage.pixel( x, y ) == Qt::black )     // check wether working right!
             secondaryImage.setPixel( x, y, transparentPixel);   
         else
             secondaryImage.setPixel( x, y, redPixel );
    }
}

---

---

Added after 27 minutes:

change following line

Code:

---

if ( secondaryImage.pixel( x, y ) == Qt::black )

---

to

Code:

---

if ( secondaryImage.pixel( x, y ) == QRgb( #000000 )   // black

---

here is an example which shows you how to convert color mode. i t helps you convert between white and black,RGB and other image formats. and the above pixel color changing make sense as well.
hope i am being helpful.
best luck to you
Lily