PAM: a simple RGB+ALPHA file format

To create images with transparencies without too much scaffolding, use the netpgm-associated format PAM, and then use pamtotiff.

#include 

int main() {
    
    printf("P7\n");
    printf("WIDTH 256\n");
    printf("HEIGHT 256\n");
    printf("DEPTH 4\n");
    printf("MAXVAL 255\n");
    printf("TUPLTYPE RGB_ALPHA\n");
    printf("ENDHDR\n");

    unsigned int row,col;
    for (row=0; row<256; row++) {
    for (col=0; col<256; col++) {
        
        printf("%c", (char)col);         // RED
        printf("%c", (char)(255-col));   // GREEN
        printf("%c", (char)row);         // BLUE
        printf("%c", (char)(255-row));   // OPACITY

    }}
    
    return 0;

}