Picture

Payx

@mrjj i cut my picture in square 4x4, and with this square i just calculate the most contained color, i replace all this square by the color and it give me a simple square with just one color

SGaist

Hi,

Why not use QImage::scaled ?

Payx

@SGaist I don't know if it will work (im a beginner) but the function return only one square ? or i can use this function to cut in 4x4 square my picture with a double "for" ?

SGaist

It was just for the resizing part.

For the processing itself, it might be better to use a library like OpenCV which likely already implement what you need.

Payx

@SGaist ok i will install OpenCV on Qt and come if i need more help

Payx

@SGaist there is a lot of tutorial for install OpenCV, and they are all different... can you have a good tutorial to show me ?

mrjj

@Payx
Hi
can i ask what effect you are after ?
It sounds like you want to make the image more pixelated?

SGaist

What OS are you on ?

Payx

@mrjj No,

I got an image, i just want to cut the image in square 4x4 (pixels) and with this square, i want to detect the most contained color. When i have this color i replace entirely the square by the color.

Exemple : if i got an image, if the first square 4x4 i have on the image is contained by 80% of red, that will replace the entirely square by red only.

This project is to have a "simple" picture.

with this simple picture i can reproduce it with candies (for exemple). Because if i got 800800 pixels i can't buy 800800 candies so i have to "reduce" it

Im on windows 10

SGaist

Then you can use the OpenCV installer, just ensure that you have an OpenCV version built with the same compiler you are using with Qt.

Payx

@SGaist I spoke with my teacher, he told me we dont need OpenCV

SGaist

I never said you needed it just that it might be simpler through it.

In any case, you can use QImage::pixelColor to get the color of one pixel of your image and then do the calculation with the surrounding pixels.

Payx

@SGaist said in Picture:

QImage::pixelColor

Ok, i will try to use it tomorrow, but i already have a question, i can't use a function in the "void MainWindow::on_push_clicked()" no ?

kshegunov

@Payx said in Picture:

I got an image, i just want to cut the image in square 4x4 (pixels) and with this square, i want to detect the most contained color. When i have this color i replace entirely the square by the color.
Exemple : if i got an image, if the first square 4x4 i have on the image is contained by 80% of red, that will replace the entirely square by red only.
This project is to have a "simple" picture.
with this simple picture i can reproduce it with candies (for exemple). Because if i got 800800 pixels i can't buy 800800 candies so i have to "reduce" it

It sounds to me you're after color space reduction after scaling. Just resample the image to the desired resolution with QImage::scaled as @SGaist suggested. Then the color space reduction boils down to calculating distances in 3 dimensional rectangular coordinate system (colors are vectors in RGB space). Suppose you have a table of 32 colors and an image:

QImage image;

const qint32 colorTableSize = 32;
QColor colorTable[colorTableSize] = { Qt::Red, Qt::Blue, ... };

Then for each pixel you choose the color from the table that's closest in the color space:

// Just go around the image
for (qint32 y = 0, height = image.height(); y < height; y++)  {
    for (qint32 x = 0, width = image.width(); x < width; x++)  {
        QColor pixel = image.pixelColor(x, y);

        // Find the closest match from the table
        qint32 colorIndex = 0;
        qreal minDistance = std::sqrt(3); // Initial value is the longest possible distance
        for (qint32 i = 0; i < colorTableSize; i++)  {
            qreal distance = QVector3D(pixel.redF() - colorTable[i].redF(), pixel.greenF() - colorTable[i].greenF(), pixel.blueF() - colorTable[i].blueF()).length();
            if (distance < minDistance)  {  // Found a closer color than the currently selected
                minDistance = distance;
                colorIndex = i;
            }
        }

        // Now just replace the pixel color with the one from the table
        image.setPixelColor(x, y, colorTable[colorIndex]);
    }
}

This doesn't take into account the disparity of color sensitivity of the human eye. If you need to account for this then you need to dig deeper to find more accurate color distances, e.g. by implementing some sort of a chromaticity diagram.

Kind regards.

jsulm

@Payx said in Picture:

i can't use a function in the "void MainWindow::on_push_clicked()" no ?

Sure you can, why not?

Payx

I just dont understand what your program do..

i got my image into my :

void MainWindow::on_push_clicked()

when i want to use it in :

void MainWindow::on_push2_clicked()

he say that my image isnt declared.

@kshegunov sorry, I just dont understand what your program do..

i thought use a thing like this :

void MainWindow::on_push2_clicked()
   {



       for (int i=0;i<pix.width()+1;i=i+4){
           for (int j=0;j<pix.height()+1;j=j+4){
               for(int x=0; x<i;x=x+1){
                  for (int z=0; z<j; z=z+1){
           
   }
}
}

and in that i will calculate the most contained color ( i thought with RGB ) and if my square is contained by 80% of red, replace it with red.

jsulm

@Payx If you get your image in

void MainWindow::on_push_clicked()

and you need it in

void MainWindow::on_push2_clicked()

then in on_push_clicked() you need to store the image somewhere, so on_push2_clicked() can use it later. You can just add a member variable to MainWindow:

class MainWindow...
{
...
private:
    QImage image;
}

Payx

@jsulm ok thank you !

For calculate the color of each pixel, what function can i use?

jsulm

@Payx Do you mean to get the pixel value? http://doc.qt.io/qt-5/qimage.html#pixel-1
It returns http://doc.qt.io/qt-5/qcolor.html#QRgb-typedef containing the RGB values, then you can calculate what ever you need.
#AARRGGBB

quint32 rgb = static_cast<quint32>(image.pixel(x, y));
int blue = rgb & x000000FF;
int green = (rgb & 0x0000FF00)>>8;
int red = (rgb & 0x00FF0000)>>16;

kshegunov

@jsulm said in Picture:

quint32 rgb = static_cast<quint32>(image.pixel(x, y));
int blue = rgb & x000000FF;
int green = (rgb & 0x0000FF00)>>8;
int red = (rgb & 0x00FF0000)>>16;

There are the (inline) qRed(), qGreen() and qBlue() for that purpose, no need for bit-magic. :)