该函数 是输入图片的字节流 然后再内部转换后输出文件的字节流
头文件部分

    /*!* @brief compressImage* @param format    图片的压缩格式* @param imageByteArray    源图像字节流* @param fileSize  压缩指定的文件大小 默认180kb* @param limitHeight 限制图片的高度* @return QByteArray  压缩后的图片字节流*/static QByteArray compressImage(const QByteArray imageByteArray, const char *format = nullptr, int fileSize = 180 * 1024, int limitHeight = 1000);

实现部分

QByteArray ImageUtil::compressImage(const QByteArray imageByteArray, const char *format, int fileSize, int limitHeight) {qInfo() << "传入图片大小" << imageByteArray.size();if (imageByteArray.size() < fileSize) {qInfo() << "图片满足要求,无需压缩";return imageByteArray;}qInfo() << "开始压缩图片";int quality = 100;QImage srcImg;QPixmap pixmap;srcImg.loadFromData(imageByteArray);QBuffer buff;double scale = 1;QSize imgSize = srcImg.size();// 压缩图片的尺寸 控制在limitHeight以内if (imgSize.height() > limitHeight)scale = ( double )limitHeight / ( double )imgSize.height();imgSize = imgSize.scaled(imgSize.width() * scale, imgSize.height() * scale, Qt::IgnoreAspectRatio);// 图片等比例缩放pixmap = pixmap.fromImage(srcImg.scaled(imgSize, Qt::IgnoreAspectRatio, Qt::FastTransformation));// 压缩图片的质量 控制在fileSize之内qint64 fsz;while (true) {QBuffer tempBuff;// 图片降低质量bool isOk = pixmap.save(&tempBuff, format, quality);quality = quality - 2;if (quality <= 0)break;fsz = tempBuff.size();if (isOk) {if (fsz <= fileSize) {pixmap.save(&buff, format, quality);break;}}}qInfo() << "现在图片大小" << fsz << "要求图片大小" << fileSize << "质量系数" << quality << "图片宽高" << imgSize.width() << imgSize.height();return buff.data();
}