QImage padding - any function availavble? - c++

Question

Is there any function which I can use in order to pad my QImage object?
I have tried to search over the net unsuccefuly.
Thx in advance.
Here is my code:
#include "mainwindow.h"
#include <QApplication>
#include "qimage.h"
#include <QImage>
#include <QLabel>
#include <QColor>
#include "qcolor.h"
#include <Qdebug>
#include <QGraphicsPixmapItem>
#include <QGraphicsScene>
#include <QGraphicsView>
int main(int argc, char *argv[])
{
printf("Init!");
qDebug() << "C++ Style Debug Message";
QApplication a(argc, argv);
QGraphicsScene scene;
QGraphicsView view(&scene);
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;
qDebug() << "Begin For Loop";
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++;
}
}
qDebug() << "Finished First Loop!";
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));
img.setPixel(col, row, clrCurrent.rgba());
p++;
}
}
QPixmap pixmap = QPixmap::fromImage(img);
QGraphicsPixmapItem *item = new QGraphicsPixmapItem(pixmap);
scene.addItem(item);
view.show();
return a.exec();
}
Hi I edited my question, i added my code in order to give you more feeling of what is going on. any help would be appreciated.

Answer 1

The QImage offers no way to change its size. You need to create a new, larger image, erase its contents, start a QPainter on it, then draw the source image in the center of the new image. That way you'll have padding.
Below is a function that returns a padded version of the image, with a given color used for padding, and a test harness for it.
// https://github.com/KubaO/stackoverflown/tree/master/questions/image-pad-35968431
#include <QtGui>
template <typename T>
QImage paddedImage(const QImage & source, int padWidth, T padValue) {
QImage padded{source.width() + 2*padWidth, source.height() + 2*padWidth, source.format()};
padded.fill(padValue);
QPainter p{&padded};
p.drawImage(QPoint(padWidth, padWidth), source);
return padded;
}
int main() {
QImage source{64, 64, QImage::Format_ARGB32_Premultiplied};
source.fill(Qt::red);
auto padded = paddedImage(source, 16, Qt::blue);
padded.save("test.png");
}
Output: