I searched in INTERNET related to the subject but I found only people that want to save png file with the background transparent.

I report belove the source code that at the moment I use and produces png with background transparent:

```
cairo_surface_t *surface; // Declarations
cairo_t *cr;

// Creations of the surface
surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32,3508,2480);

// Contest
cr = cairo_create(surface);

// Moving the plot to center in the page
cairo_translate(cr, 200,200);

// Scaling the plot
cairo_scale(cr,1.8,1.8);

// Make all the necessary actions to produce the plot 
do_drawing(cr);

// write the plot on the file png
cairo_surface_write_to_png(surface, "image.png");

// End
cairo_surface_destroy(surface);
cairo_destroy(cr);

```

I used also the surface CAIRO\_FORMAT\_RGB24 but I obtain a black rectangle like plot.

Please could you help me?
Thank You