FxGen

I wrote this yesterday as I was wondering the same thing. You can just extend the example code slightly and add this in at the end (or iterate over all the operations and save those with the GetName() value of "Store Result").

typedef struct {
char idlength;
char colourmaptype;
char datatypecode;
short int colourmaporigin;
short int colourmaplength;
char colourmapdepth;
short int x_origin;
short int y_origin;
short width;
short height;
char bitsperpixel;
char imagedescriptor;
} TGAHeader;

void writeTGA(NOperator* op, std::string path = "") {

NBitmap* pbmp = (NBitmap*)op->m_pObj;

TGAHeader header;
header.idlength=0;
header.colourmaptype=0;
header.datatypecode=2;
header.colourmaporigin=0;
header.colourmaplength=0;
header.colourmapdepth=0;
header.x_origin=0;
header.y_origin=0;
header.width = (short)pbmp->GetWidth();
header.height = (short)pbmp->GetHeight();
header.bitsperpixel= 32;
header.imagedescriptor=0;

std::string tganame (path);
if(tganame.size()>0) tganame += "\\";
tganame += op->GetUserName();
tganame += ".tga";

FILE* tgaf = fopen(tganame.c_str(),"wb");
fwrite(&header.idlength, 1, 1, tgaf);
fwrite(&header.colourmaptype, 1, 1, tgaf);
fwrite(&header.datatypecode, 1, 1, tgaf);
fwrite(&header.colourmaporigin, 2, 1, tgaf);
fwrite(&header.colourmaplength, 2, 1, tgaf);
fwrite(&header.colourmapdepth, 1, 1, tgaf);
fwrite(&header.x_origin, 2, 1, tgaf);
fwrite(&header.y_origin, 2, 1, tgaf);
fwrite(&header.width, 2, 1, tgaf);
fwrite(&header.height, 2, 1, tgaf);
fwrite(&header.bitsperpixel, 1, 1, tgaf);
fwrite(&header.imagedescriptor, 1, 1, tgaf);

RGBA* pixels = pbmp->GetPixels();

char* offset=0;
for(int y=header.height-1;y>0;y--) {
offset = (char*) pixels + y*header.width*4;
for(int x=0;x<header.width;x++) {
offset += 4;
fwrite(offset+2, 1, 1, tgaf);
fwrite(offset+1, 1, 1, tgaf);
fwrite(offset, 1, 1, tgaf);
fwrite(offset+3, 1, 1, tgaf);
}
}

fclose(tgaf);
}