diff --git a/src/gfx/process.cpp b/src/gfx/process.cpp
index bbd86b02..06678845 100644
--- a/src/gfx/process.cpp
+++ b/src/gfx/process.cpp
@@ -689,17 +689,15 @@ static void outputUnoptimizedTileData(
 		// LCOV_EXCL_STOP
 	}
 
-	uint64_t widthTiles = options.inputSlice.width ? options.inputSlice.width : image.png.width / 8;
-	uint64_t heightTiles =
-	    options.inputSlice.height ? options.inputSlice.height : image.png.height / 8;
-	uint64_t nbTiles = widthTiles * heightTiles;
-	uint64_t nbKeptTiles = nbTiles > options.trim ? nbTiles - options.trim : 0;
-	uint64_t tileIdx = 0;
+	size_t nbTiles = std::count_if(RANGE(attrmap), [](AttrmapEntry const &attr) {
+		return !attr.isBackgroundTile();
+	});
+	size_t nbKeptTiles = nbTiles > options.trim ? nbTiles - options.trim : 0;
+	size_t tileIdx = 0;
 
 	for (auto const &[tile, attr] : zip(image.visitAsTiles(), attrmap)) {
 		// Do not emit fully-background tiles.
 		if (attr.isBackgroundTile()) {
-			++tileIdx;
 			continue;
 		}
 
@@ -918,9 +916,9 @@ static void outputTileData(UniqueTiles const &tiles) {
 		// LCOV_EXCL_STOP
 	}
 
-	uint64_t nbTiles = tiles.size();
-	uint64_t nbKeptTiles = nbTiles > options.trim ? nbTiles - options.trim : 0;
-	uint64_t tileIdx = 0;
+	size_t nbTiles = tiles.size();
+	size_t nbKeptTiles = nbTiles > options.trim ? nbTiles - options.trim : 0;
+	size_t tileIdx = 0;
 
 	for (TileData const *tile : tiles) {
 		assume(tile->tileID == tileIdx);
diff --git a/test/gfx/trim_with_bg.flags b/test/gfx/trim_with_bg.flags
new file mode 100644
index 00000000..2f817917
--- /dev/null
+++ b/test/gfx/trim_with_bg.flags
@@ -0,0 +1,3 @@
+-B #ff00ff
+-x 1
+ 
\ No newline at end of file
diff --git a/test/gfx/trim_with_bg.out.2bpp b/test/gfx/trim_with_bg.out.2bpp
new file mode 100644
index 00000000..2d7b07f8
Binary files /dev/null and b/test/gfx/trim_with_bg.out.2bpp differ
diff --git a/test/gfx/trim_with_bg.out.attrmap b/test/gfx/trim_with_bg.out.attrmap
new file mode 100644
index 00000000..593f4708
Binary files /dev/null and b/test/gfx/trim_with_bg.out.attrmap differ
diff --git a/test/gfx/trim_with_bg.out.palmap b/test/gfx/trim_with_bg.out.palmap
new file mode 100644
index 00000000..593f4708
Binary files /dev/null and b/test/gfx/trim_with_bg.out.palmap differ
diff --git a/test/gfx/trim_with_bg.out.tilemap b/test/gfx/trim_with_bg.out.tilemap
new file mode 100644
index 00000000..fb194a50
Binary files /dev/null and b/test/gfx/trim_with_bg.out.tilemap differ
diff --git a/test/gfx/trim_with_bg.png b/test/gfx/trim_with_bg.png
new file mode 100644
index 00000000..e2ec037e
Binary files /dev/null and b/test/gfx/trim_with_bg.png differ
diff --git a/test/gfx/trim_with_bg_dedup.flags b/test/gfx/trim_with_bg_dedup.flags
new file mode 100644
index 00000000..8067608f
--- /dev/null
+++ b/test/gfx/trim_with_bg_dedup.flags
@@ -0,0 +1,4 @@
+-B #ff00ff
+-x 1
+-u
+ 
\ No newline at end of file
diff --git a/test/gfx/trim_with_bg_dedup.out.2bpp b/test/gfx/trim_with_bg_dedup.out.2bpp
new file mode 100644
index 00000000..2d7b07f8
Binary files /dev/null and b/test/gfx/trim_with_bg_dedup.out.2bpp differ
diff --git a/test/gfx/trim_with_bg_dedup.out.attrmap b/test/gfx/trim_with_bg_dedup.out.attrmap
new file mode 100644
index 00000000..593f4708
Binary files /dev/null and b/test/gfx/trim_with_bg_dedup.out.attrmap differ
diff --git a/test/gfx/trim_with_bg_dedup.out.palmap b/test/gfx/trim_with_bg_dedup.out.palmap
new file mode 100644
index 00000000..593f4708
Binary files /dev/null and b/test/gfx/trim_with_bg_dedup.out.palmap differ
diff --git a/test/gfx/trim_with_bg_dedup.out.tilemap b/test/gfx/trim_with_bg_dedup.out.tilemap
new file mode 100644
index 00000000..fb194a50
Binary files /dev/null and b/test/gfx/trim_with_bg_dedup.out.tilemap differ
diff --git a/test/gfx/trim_with_bg_dedup.png b/test/gfx/trim_with_bg_dedup.png
new file mode 100644
index 00000000..e2ec037e
Binary files /dev/null and b/test/gfx/trim_with_bg_dedup.png differ