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)