Trying to remove background and make it transparent in c++, using magick++ - c++

Question

I am having an image "objects.png" with a red background and I'm trying to make the background transparent. The code is straight forward but somehow I am not able to get the desired result. I am quite new to this ImageMagick business and this is my first program using Magick++. So, it would be great if you can explain things in detail. Thanks in advance. Code goes like this,
#include <iostream>
#include <Magick++.h>
using namespace std;
using namespace Magick;
int main(){
Image my_image("objects.png");
Color bg_color = my_image.pixelColor(0,0);
Color new_bg_color(0, MaxRGB, 0, MaxRGB);
for (int i=0;i<my_image.columns();i++){
for (int j=0;j<my_image.rows();j++){
//cout<<"(i,j) : ("<<i<<","<<j<<")\n";
if (my_image.pixelColor(i,j) == bg_color){
my_image.pixelColor(i,j,new_bg_color);
}
}
}
my_image.write("new_objects.png");
}
Image objects.png is
and I'm getting this as output

Answer 1

I think there is a Magick::Image.transparent method that should handle transparency assignment.
#include <iostream>
#include <Magick++.h>
using namespace std;
using namespace Magick;
int main(){
Image my_image("objects.png");
Color bg_color = my_image.pixelColor(0,0);
my_image.transparent(bg_color);
my_image.write("new_objects.png");
}
Edit
To allow the Magick::Color's opacity to be respected. You need to enable the alpha channel of the image by setting Magick::Image.matte, or Magick::Image.opacity attributes.
#include <iostream>
#include <Magick++.h>
using namespace std;
using namespace Magick;
int main(){
Image my_image("objects.png");
Color bg_color = my_image.pixelColor(0,0);
Color new_bg_color(0, MaxRGB, 0, MaxRGB);
my_image.matte(true); // or my_image.opacity();
for (int i=0;i<my_image.columns();i++){
for (int j=0;j<my_image.rows();j++){
if (my_image.pixelColor(i,j) == bg_color){
my_image.pixelColor(i,j,new_bg_color);
}
}
}
my_image.write("new_objects.png");
}