Saving a JPG from a BMP using GDI+ with a set DPI - jpeg

Question

I have an image in BMP form and I want a C++ program to save it to JPG using GDI+, after reading some GDI+ documentation I came up with this program:
#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;
EncoderParameters encoderParameters;
ULONG quality;
Image* image = new Gdiplus::Image(L"plot.bmp");
// 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 = image->Save(L"plot100.jpg", &encoderClsid, &encoderParameters);
if (stat == Ok)
printf("plot.jpg was saved successfully\n");
else
printf("Failure: stat = %d\n", stat);
delete image;
GdiplusShutdown(gdiplusToken);
return;
}
int main()
{
SaveFile();
return 0;
}
But the image is saving with a horizontal and vertical resolution of 7dpi no matter what the value of "quelity" is, I need to save the jpg with a 96dpi, how can I set that?
Thank you in advance.

Answer 1

A modified version of the function SaveFile() solved the problem:
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 = 72;
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;
}