I think Imager is good enough for this task. Though starting point looks strange to me, but assuming there already is, as in OP, a Perl array of (unusual) ARGB packed colour values, read the 4 channels, then just drop useless 0th channel. Otherwise the hassle with "combine" (or something similar, TMTOWTDI), etc. is unnecessary, of course.

use strict;
use warnings;
use Imager;

use constant IMAGESIZE => 300;
use constant ROSYBROWN => 0x00BC8F8F;

my @result = map {              # make us some picture to find when
    ( ROSYBROWN ) x $_,         # examining output, let it be random
    int( rand 0xFFFFFFFF ),     # colour diagonal on uniform BG
    ( ROSYBROWN ) x ( IMAGESIZE - $_ - 1 ), 
} 0 .. IMAGESIZE - 1;

my $img = Imager-> new(
    type  => 'raw',
    xsize => IMAGESIZE,
    ysize => IMAGESIZE,
    data  => pack( 'L>*', @result ),
    raw_interleave    => 0,
    raw_datachannels  => 4, 
    raw_storechannels => 4,
);
Imager-> combine( src      => [ $img, $img, $img ],
                  channels => [ 1, 2, 3 ],
)-> write( file => 'test.png' );
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