HV* countColors2( SV *img ) {
    STRLEN l;
    U32 *rgba = (U32*)SvPVx( img, l ), i;
    HV* counts = newHV();

    l /= 4;
    for( i = 0; i < l; ++i ) {
        SV **val;
        if( val = hv_fetch( counts, (char*)&rgba[ i ], 4, 0 ) ) {
            SvIV_set( *val, SvIV( *val ) + 1 );
        }
        else {
            SV *val = newSViv( 1 );
            hv_store( counts, (char*)&rgba[ i ], 4, val, 0 );
        }
    }
    return counts;
}


##</code><code>##

C:\test>1138218 mid.png
Width:12800 height:10240 pixels:131072000
Took 12.642578 seconds
Found 81814 colors in 131072000 pixels