Qt实现将PDF文件转高清图片的完整指南

#include <QScreen>
#include <QPdfDocument>
#include <QPdfDocumentRenderOptions>
#include <QImage>
#include <QFile>
#include <QDir>
#include <QGuiApplication>
#include <QPainter>


#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

bool MainWindow::pdfToHighResImage(const QString &pdfPath,
                                   const QString &imgPath,
                                   QSize size,int dpi)
{
    QPdfDocument doc;
    auto err = doc.load(pdfPath);
    if (err != QPdfDocument::Error::None)
    {
        qDebug() << "load pdf error code:" << err;
        return false;
    }

    // 校验自定义尺寸
    if (!size.isValid() || size.width() <= 0 || size.height() <= 0)
    {
        qDebug() << "input size width or height less zero!";
        doc.close();
        return false;
    }

    // 拆分路径，自动创建目录
    QFileInfo imageFileInfo(imgPath);
    // 获取后缀并判断格式
    QString suffix = imageFileInfo.suffix().toLower();
    QString imgFormat;
    int quality = -1;
    if (suffix == "png")
    {
        imgFormat = "PNG";
    }
    else if (suffix == "jpg" || suffix == "jpeg")
    {
        imgFormat = "JPG";
        quality = 100; // jpg最高画质防模糊
    }
    else
    {
        qDebug() << "unsupported image extensions, only png / jpg / jpeg are supported!";
        doc.close();
        return false;
    }
    // 只转换第0页（如需指定页码可再加pageIndex参数）
    int pageIdx = 0;
    qDebug()<<doc.pagePointSize(pageIdx);
    QPdfDocumentRenderOptions opts;
    opts.setRenderFlags(QPdfDocumentRenderOptions::RenderFlag::None );
    QImage img = doc.render(pageIdx, size, opts);
    if (img.isNull())
    {
        qDebug() << "page " << pageIdx + 1 << " rendering failed!";
        doc.close();
        return false;
    }
    QImage whiteBgImg(size, QImage::Format_RGB32); // RGB无透明通道
    whiteBgImg.fill(Qt::white); // 铺满纯白色背景
    QPainter painter(&whiteBgImg);
    painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);
    painter.drawImage(0, 0, img); // 将带透明的PDF图绘制到白底上
    painter.end();
    // 替换原img，后续保存用白底图
    img = std::move(whiteBgImg);

    int dotsPerMeter = qRound(dpi / 25.4 * 1000);
    img.setDotsPerMeterX(dotsPerMeter);
    img.setDotsPerMeterY(dotsPerMeter);
    if (imgFormat == "PNG")
    {
        // PNG额外写入文本信息，看图软件可识别
        img.setText("DPI", QString::number(dpi));
    }
    bool saveOk;
    if (quality > 0)
        saveOk = img.save(imgPath, imgFormat.toUtf8().data(), quality);
    else
        saveOk = img.save(imgPath, imgFormat.toUtf8().data());

    if (!saveOk)
        qDebug() << "failed to save the image:" << imgPath;
    else
        qDebug() << "success to save the image:" << imgPath;

    doc.close();
    return saveOk;
}
void MainWindow::on_pushButton_clicked()
{
    pdfToHighResImage("L000137362.pdf", "L000137362.jpg", QSize(896,1534),300);
    pdfToHighResImage("L000137362.pdf", "L000137362.png", QSize(896,1534),300);
}

QT += pdf

find_package(Qt6 REQUIRED COMPONENTS Pdf)
target_link_libraries(your_target PRIVATE Qt6::Pdf)