利用gdi+转换图片,从png转到jpg时,透明的部分变成黑色而不是白色了.

[szuzsq]

int GetEncoderClsid(const wchar_t* format, CLSID* clsid) {
	unsigned int num = 0;
	unsigned int size = 0;
	GetImageEncodersSize(&num, &size);
	if(size == 0) return -1;
	
	ImageCodecInfo* pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
	if(pImageCodecInfo == 0) return -1;
	GetImageEncoders(num, size, pImageCodecInfo);
	
	for(unsigned int j = 0; j < num; ++j) {
		if(wcscmp(pImageCodecInfo[j].MimeType, format) == 0) {
			*clsid = pImageCodecInfo[j].Clsid;
			free(pImageCodecInfo);
			return j;
		}
	}
	
	free(pImageCodecInfo);
	return -1;
}

void SaveBMP(Image* image, const wchar_t* fn) {
	CLSID clsid;
	GetEncoderClsid(L"image/bmp", &clsid);
	image->Save(fn, &clsid, NULL);
}

void SaveJPG(Image* image, const wchar_t* fn) {
	CLSID clsid;
	GetEncoderClsid(L"image/jpeg", &clsid);
	image->Save(fn, &clsid, NULL);
}

void SaveGIF(Image* image, const wchar_t* fn) {
	CLSID clsid;
	GetEncoderClsid(L"image/gif", &clsid);
	image->Save(fn, &clsid, NULL);
}

void SaveTIF(Image* image, const wchar_t* fn) {
	CLSID clsid;
	GetEncoderClsid(L"image/tiff", &clsid);
	image->Save(fn, &clsid, NULL);
}

void SavePNG(Image* image, const wchar_t* fn) {
	CLSID clsid;
	GetEncoderClsid(L"image/png", &clsid);
	image->Save(fn, &clsid, NULL);
}



//用法如下:
	Bitmap source(name.c_str());

		if(sub_ext == L".png")
			SavePNG(source, sub_fn.c_str());
		else if(sub_ext == L".jpg" || sub_ext == L".jpeg")
			SaveJPG(source, sub_fn.c_str());
		else if(sub_ext == L".bmp")
			SaveBMP(source, sub_fn.c_str());
		else if(sub_ext == L".gif")
			SaveGIF(source, sub_fn.c_str());
		else if(sub_ext == L".tif" || sub_ext == L".tiff")
			SaveTIF(source, sub_fn.c_str());

[Yofoo]

png自身的应该是透明的, 不是白色, 也不是黑色 保存到jpg如果想要某个背景颜色可以创建一个Graphics , 先填充背景颜色, 然后绘制png, 最后导出来

[kgd329443091]

一楼正解 先画底图 再绘出png 再转存

[赵4老师]

小心底图内容手滑初始化为无底裤图了！

[szuzsq]

谢谢楼上诸位,我走弯路了.我每个象素将apha值转成灰度.