CODEWITHSUNDEEP
c++qtgrayscaleqimagepixel-manipulation
Daniel Eitan
Daniel Eitan

Reputation: 45

Qt - displaying unsigned char after pixel manipulation

I'm trying to display my manipulated pixels (gray scale them) which is represented as unsigned char unsuccefully.

Here is the code:

#include "mainwindow.h"
#include <QApplication>
#include "qimage.h"
#include <QImage>
#include <QLabel>
#include <QColor>
#include "qcolor.h"
#include <Qdebug>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    int height;
    int width;
    unsigned char *p, *p_begin;
    QImage img("C:\\Users\\Owner\\Pictures\\2013-09-26\\IMG_0836.JPG");
    height = img.height();
    width = img.width();

    p = (unsigned char *)malloc(height * width * sizeof(unsigned char));
    p_begin = p;

    for (int row = 0; row < height; ++row)
    {
        for (int col = 0; col < width; ++col)
        {
            QColor clrCurrent( img.pixel( col, row ));
            *p = (unsigned char)((clrCurrent.green() * 0.587) + (clrCurrent.blue() * 0.114) + (clrCurrent.red() * 0.299));
            p++;
        }
    }

    p = p_begin;
    for ( int row = 0; row < height; ++row )
    {
        for (int col = 0; col < width; ++col)
        {
            QColor clrCurrent(img.pixel(col, row));

            clrCurrent.setBlue((int)(*p));
            clrCurrent.setGreen((int)(*p));
            clrCurrent.setRed((int)(*p));
            p++;
        }

    }
    QLabel myLabel;
    myLabel.setPixmap(QPixmap::fromImage(img));
    myLabel.show();

    return a.exec();
}

I dont really know why but the picture which represented is the original picture and not the manipulated one, which should be gray scaleded. I tried to find over the net with no luck, any ideas? Thx in advance.

Upvotes: 0

Views: 225

Answers (1)

johngull
johngull

Reputation: 829

This part of code:

QColor clrCurrent(img.pixel(col, row));

clrCurrent.setBlue((int)(*p));
clrCurrent.setGreen((int)(*p));
clrCurrent.setRed((int)(*p));
p++;

doesn't change img. It just take pixel color to temporary object, change that object, then this object is just destroyed without influence to the image.

I recommend you to check function scanLine of QImage. And then change color of pixels in one for loop on the place. This will works much faster and will change image.

Upvotes: 3

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