当使用GDI +和通过jagPDF创建的pdf保存时，在Cimg上创建的图像在pdf上显示时不同

我需要做的非常简单，我需要使用CIMG绘制矢量，然后将图形保存为jpg，然后使用JAGPDF将jpg添加到PDF文档中。为了将CIMG保存为JPG，该程序使用了一个名为Image Magick的外部程序。

我想避免使用该程序，而是先将CIMG另存为BMP（本机执行此操作），然后再从bmp保存jpg，从而避免使用GDI +。

MCVE程序看起来像这样

#include "CImg.h"
#include <jagpdf/api.h>
#include <vector>

using namespace jag;
using namespace cimg_library;

int main(int argc, char** const argv)
{

    const float x0 = 0;
    const float x1 = 9;
    const int resolution = 5000;

    // Create plot data.
    CImg<double> values(1, resolution, 1, 1, 0);

    const unsigned int r = resolution - 1;

    for (int i1 = 0; i1 < resolution; ++i1)
    {
        double xtime = x0 + i1*(x1 - x0) / r;
        values(0, i1) = 2 * sin(xtime);
    }

    CImg<unsigned char> graph;
    graph.assign(750, 240, 1, 3, 255);

    static const unsigned char black[] = { 0, 0, 0 }, white[] = { 255, 255, 255 };
    static const unsigned char red[] = { 255, 200, 200 }, bred[] = { 255, 0, 0 };

    graph.draw_grid(6, 6, 0, 0, false, true, red, 10.0f, 0xFFFFFFFF, 0xFFFFFFFF);
    graph.draw_grid(30, 30, 0, 0, false, true, bred, 10.0f, 0xFFFFFFFF, 0xFFFFFFFF);

    graph.draw_graph(values, black, 1, 1, 1, 2, -2, 0xFFFFFFFF);;

    //////////////Method 1: Using Image Magick////////////////
    graph.save_jpeg("plot2.jpg");

    pdf::Document doc(pdf::create_file("report.pdf"));
    doc.page_start(848.68, 597.6);
    pdf::Image imag2 = doc.image_load_file("plot2.jpg");
    doc.page().canvas().image(imag2, 50, 50);
    doc.page_end();
    doc.finalize();
    //////////////Method 2: Using GDI+////////////////
    graph.save("plot.bmp");
    SaveFile();
    pdf::Document doc2(pdf::create_file("report2.pdf"));
    doc2.page_start(848.68, 597.6);
    pdf::Image imag = doc2.image_load_file("plot.jpg");
    doc2.page().canvas().image(imag, 50, 50);
    doc2.page_end();
    doc2.finalize();

    return 0;
}

SaveFile（）是以下函数，使用GDI +从plot.bmp转换为plot.jpg

#include <windows.h>
#include <objidl.h>
#include <gdiplus.h>
#include "GdiplusHelperFunctions.h"


#pragma comment (lib,"Gdiplus.lib")

VOID SaveFile()
{
    // Initialize GDI+.
    Gdiplus::GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    CLSID   encoderClsid;
    Status  stat;
    Image*   image = new Gdiplus::Image(L"plot.bmp");

    // Get the CLSID of the PNG encoder.
    GetEncoderClsid(L"image/jpeg", &encoderClsid);

    stat = image->Save(L"plot.jpg", &encoderClsid, NULL);

    if (stat == Ok)
        printf("plot.jpg was saved successfully\n");
    else
        printf("Failure: stat = %d\n", stat);

    delete image;
    GdiplusShutdown(gdiplusToken);
    }

两种方法都保存了属性中似乎具有相同大小的jpgs，但是第一种方法将图像正确地放置在pdf中，而第二种方法将大图像放置在pdf中，即使它们被假定为相同的大小。我怎样才能解决这个问题？

随附的是report1和report2的快照

解决方案

根据您的建议，我能够修改SaveFile函数以控制de DPI，并在有人需要时发布了新代码。

VOID SaveFile()
{
    // Initialize GDI+.
    Gdiplus::GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    CLSID   encoderClsid;
    Status  stat;
    EncoderParameters encoderParameters;
    ULONG    quality;

    Gdiplus::Bitmap*   bitmap = new Gdiplus::Bitmap(L"plot.bmp");
    Gdiplus::REAL dpi = 96;
    bitmap->SetResolution(dpi,dpi);


    // Get the CLSID of the PNG encoder.
    GetEncoderClsid(L"image/jpeg", &encoderClsid);

    encoderParameters.Count = 1;
    encoderParameters.Parameter[0].Guid = EncoderQuality;
    encoderParameters.Parameter[0].Type = EncoderParameterValueTypeLong;
    encoderParameters.Parameter[0].NumberOfValues = 1;

   quality = 100;
   encoderParameters.Parameter[0].Value = &quality;

   stat = bitmap->Save(L"plot.jpg", &encoderClsid, &encoderParameters);


   if (stat == Ok)
        printf("plot.jpg was saved successfully\n");
   else
        printf("Failure: stat = %d\n", stat);

   delete bitmap;
   GdiplusShutdown(gdiplusToken);
   return;
}