Upgrade Group4Reader dimensions from u16 to u32

tests/decode_images.rs

@@ -720,3 +720,24 @@ fn extra_bits_gray() {
 fn extra_bits_rgb() {
     test_image_sum_u8("extra_bits_rgb_8b.tiff", ColorType::RGB(8), 0);
 }
+
+
+#[test]
+#[cfg(feature = "fax")]
+fn test_decode_huge_g4() {
+    let path = PathBuf::from(TEST_IMAGE_DIR).join("big_g4.tif");
+    let img_file = File::open(path).expect("failed to open large G4 test image");
+    let mut decoder = tiff::decoder::Decoder::new(img_file).expect("failed to create decoder");
+
+    let (width, height) = decoder.dimensions().expect("failed to get dimensions");
+    
+    assert!(height > u16::MAX as u32, "Test image height {} is not large enough to test u16 overflow", height);
+
+    let result = decoder.read_image().expect("failed to decode huge G4 image");
+
+    if let tiff::decoder::DecodingResult::U8(data) = result {
+        assert_eq!(data.len(), (width as usize * height as usize));
+    } else {
+        panic!("Unexpected decoding result type");
+    }
+}