Expression must be a modifiable L value error - c++

Question

I am writing a code that reads a ppm file and stores the width, the height and the pixels of the file to an image object. In my image class I have a pointer that holds the image data. I also have an error in a method that sets the rgb values for a x, y pixel.
typedef load compontent_t
class Image
{
public:
enum channel_t { RED = 0, GREEN, BLUE };
protected:
component_t * buffer; //! Holds the image data.
unsigned int width, //! The width of the image (in pixels)
height; //! The height of the image (in pixels)
// data mutators
/*! Sets the RGB values for an (x,y) pixel.
*
* The method should perform any necessary bounds checking.
*
* \param x is the (zero-based) horizontal index of the pixel to set.
* \param y is the (zero-based) vertical index of the pixel to set.
* \param value is the new color for the (x,y) pixel.
*/
void setPixel(unsigned int x, unsigned int y, Color & value) {
if (x > 0 && x < width && y > 0 && y < height) {
size_t locpixel = y*width + x;
size_t componentofpixel = locpixel * 3;
*buffer + componentofpixel = value.r;
*buffer + componentofpixel + 1 = value.g;
*buffer + componentofpixel + 2 = value.b;
}
else {
cout << "Pixel out of bounds" << endl;
}
}
Image(unsigned int width, unsigned int height, component_t * data_ptr): width(width), height(height),buffer(data_ptr) {}
So in the setPixel method when i am trying to find the correct spot of the buffer to set the rgb value it shows me the error: "expression must be a modifiable L value"