Using FlexRaw to read the PV of a scalar as an ndarray is very clever, nice work! However, a more idiomatic way might be to replace the last 4 lines with (untested):

$image = zeroes byte, $im->getwidth, $im->getheight;
$im->write( data => $image->get_dataref, type => 'raw' );
$image->upd_data;
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Another way to read images into PDL with lots of capability is PDL::OpenCV::Imgcodecs.