Add image processing using opencv

image_processing/image_processing.pri

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+INCLUDEPATH += $$PWD
+DEPENDPATH += $$PWD
+
+SOURCES += \
+    $$PWD/resize_image.cpp
+
+HEADERS += \
+    $$PWD/resize_image.h
+
+# include opencv, and link against it (core and imgproc)
+# windows
+win32 {
+    INCLUDEPATH += $$PWD/opencv/build/include
+    DEPENDPATH += $$PWD/opencv/build/include
+}
+# release
+win32:CONFIG(release, debug|release) {
+
+    LIBS += -L$$PWD/opencv/build/x64/vc16/lib \
+            -lopencv_world490
+}
+# debug
+win32:CONFIG(debug, debug|release) {
+    LIBS += -L$$PWD/opencv/build/x64/vc16/lib \
+            -lopencv_world490d
+}
+
+
+#win32:CONFIG(release, debug|release): LIBS += -L$$PWD/../../../../opencv/build/x64/vc15/lib/ -lopencv_world341
+#else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/../../../../opencv/build/x64/vc15/lib/ -lopencv_world341d
+
+#INCLUDEPATH += $$PWD/../../../../opencv/build/include
+#DEPENDPATH += $$PWD/../../../../opencv/build/include

image_processing/resize_image.cpp

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+#include "resize_image.h"
+
+// include opencv
+#include <opencv2/opencv.hpp>
+
+QPixmap scalePixmapBicubic(const QPixmap &pixmap, int width, int height);
+QPixmap scalePixmapLanczos(const QPixmap &pixmap, int width, int height);
+QPixmap scalePixmapArea(const QPixmap &pixmap, int width, int height);
+QPixmap scalePixmapOpenCV(const QPixmap &pixmap, int width, int height, cv::InterpolationFlags flags);
+
+QPixmap smartScalePixmap(const QPixmap &pixmap, int width, int height)
+{
+    const int w = pixmap.width();
+    const int h = pixmap.height();
+    if ((w == width && h == height) || pixmap.isNull()) {
+        return pixmap;
+    }
+
+    if (w <= width && h <= height) { // upscaling
+        return scalePixmapLanczos(pixmap, width, height);
+    }
+
+    return pixmap;
+}
+
+QPixmap scalePixmap(const QPixmap &pixmap, int width, int height, ScaleMethod method)
+{
+    const int w = pixmap.width();
+    const int h = pixmap.height();
+    if (w == width && h == height) {
+        return pixmap;
+    }
+
+    switch (method) {
+    case ScaleMethod::QtFast:
+        return pixmap.scaled(width, height, Qt::KeepAspectRatio, Qt::FastTransformation);
+    case ScaleMethod::QtSmooth:
+        return pixmap.scaled(width, height, Qt::KeepAspectRatio, Qt::SmoothTransformation);
+    case ScaleMethod::Bicubic:
+        return scalePixmapBicubic(pixmap, width, height);
+    case ScaleMethod::Lanczos:
+        return scalePixmapLanczos(pixmap, width, height);
+    case ScaleMethod::Area:
+        return scalePixmapArea(pixmap, width, height);
+    }
+}
+
+QPixmap scalePixmapBicubic(const QPixmap &pixmap, int width, int height)
+{
+    return scalePixmapOpenCV(pixmap, width, height, cv::INTER_CUBIC);
+}
+
+QPixmap scalePixmapLanczos(const QPixmap &pixmap, int width, int height)
+{
+    return scalePixmapOpenCV(pixmap, width, height, cv::INTER_LANCZOS4);
+}
+
+QPixmap scalePixmapArea(const QPixmap &pixmap, int width, int height)
+{
+    return scalePixmapOpenCV(pixmap, width, height, cv::INTER_AREA);
+}
+
+QPixmap scalePixmapOpenCV(const QPixmap &pixmap, int width, int height, cv::InterpolationFlags flags)
+{
+    QImage qimage = pixmap.toImage();
+    cv::Mat mat = cv::Mat(qimage.height(), qimage.width(), CV_8UC4, (void *)qimage.bits(), qimage.bytesPerLine());
+
+    cv::Mat resizedMat;
+    cv::resize(mat, resizedMat, cv::Size(width, height), 0, 0, flags);
+
+    QImage resizedQImage((uchar *)resizedMat.data, resizedMat.cols, resizedMat.rows, resizedMat.step, QImage::Format_ARGB32);
+    QPixmap resizedPixmap = QPixmap::fromImage(resizedQImage);
+
+    return resizedPixmap;
+}

image_processing/resize_image.h

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+#ifndef RESIZE_IMAGE_H
+#define RESIZE_IMAGE_H
+
+#include <cmath>
+#include <QPixmap>
+#include <QImage>
+
+enum class ScaleMethod {
+    QtFast,
+    QtSmooth, // Bilinear
+    Bicubic,
+    Lanczos,
+    Area
+
+};
+
+QPixmap smartScalePixmap(const QPixmap &pixmap, int width, int height);
+QPixmap scalePixmap(const QPixmap &pixmap, int width, int height, ScaleMethod method = ScaleMethod::QtSmooth);
+
+#endif // RESIZE_IMAGE_H