diff --git a/bin/make-sizes b/bin/make-sizes
index 0ed4e62..fcbecad 100755
--- a/bin/make-sizes
+++ b/bin/make-sizes
@@ -20,8 +20,9 @@ unit sub MAIN(
   Bool :v(:$verbose) = False,
   #| out dir, default ./out
   IO(Str) :o(:$outdir) = 'out'.IO,
-  #| use a subdirectory for each site
-  Bool :d(:$subdirs) = False,
+  #| output as e.g. thing.mastodon.webp instead of mastodon/thing.webp
+  Bool :F(:$flat) = False,
+  Str :B(:$background) = 'white',
   #| defaults to all *.png & *.jpg files in the current dir
   *@files,
 );
@@ -44,13 +45,14 @@ sub to-formats($_, *@default) {
   .lc.split(',').map: { Format::{$_} // die qq/unrecognised format "$_"/ }
 }
 
-die "furaffinity/weasyl don't know what webp are" if $furaffinity ~~ /:i webp/;
 
 my @mastodon    = to-formats $mastodon,    webp;
 my @itaku       = to-formats $itaku,       webp;
 my @furaffinity = to-formats $furaffinity, png, jpg;
 my @gallery     = to-formats $gallery,     webp;
 
+die "furaffinity/weasyl don't know what webp are" if @furaffinity.any == webp;
+
 unless @files.=map(*.IO) {
   @files = $*CWD.dir: test => /:i \.[jpe?g|png]$/ && *.IO.f;
 }
@@ -60,26 +62,23 @@ for @files { die "$_ is not a regular file" unless .f; }
 # running imagemagick (and oxipng sometimes) 🪄
 
 sub convert($in, $name, $size, $format) {
-  my $out = $subdirs
-    ?? $outdir.child($name).child($in.basename).extension("$format")
-    !! $outdir.child($in.basename).extension("$name.$format");
+  my $out = $flat
+    ?? $outdir.child($in.basename).extension("$name.$format")
+    !! $outdir.child($name).child($in.basename).extension("$format");
+  my @bg-flags = «-background $background -alpha remove» if $format == jpg;
   cmd <mkdir -p>, $out.dirname;
-  cmd <convert>, $in, '-resize', $size, '-quality', $quality, $out;
+  cmd <convert>, $in, '-resize', $size, '-quality', $quality, @bg-flags, $out;
   cmd <oxipng -q>, $out if $format == png;
   $out
 }
 
-constant $SIZE           = 2800;
-constant $SQUARE         = "{$SIZE}x{$SIZE}>";
-constant $MASTO-SIZE     = "{1280²}@";
-constant $GALLERY-SIZE   = 3000;
-constant $GALLERY-SQUARE = "{$GALLERY-SIZE}x{$GALLERY-SIZE}>";
+sub square($s) { "{$s}x{$s}>" }
 
 my @sites = [
-  {:name<mastodon>,    :formats(@mastodon),    :size($MASTO-SIZE)},
-  {:name<itaku>,       :formats(@itaku),       :size($SQUARE)},
-  {:name<furaffinity>, :formats(@furaffinity), :size($SQUARE)},
-  {:name<gallery>,     :formats(@gallery),     :size($GALLERY-SQUARE)},
+  {:name<mastodon>,    :formats(@mastodon),    :size("{1280²}@")},
+  {:name<itaku>,       :formats(@itaku),       :size(square 2800)},
+  {:name<furaffinity>, :formats(@furaffinity), :size(square 1500)},
+  {:name<gallery>,     :formats(@gallery),     :size(square 3000)},
 ];