LibPDF: Handle the BlackIs1 parameter of the CCITTFaxDecode Filter

Userland/Libraries/LibPDF/Filter.cpp

@@ -276,6 +276,12 @@ PDFErrorOr<ByteBuffer> Filter::decode_run_length(ReadonlyBytes bytes)
     return TRY(Compress::PackBits::decode_all(bytes, OptionalNone {}, Compress::PackBits::CompatibilityMode::PDF));
 }
 
+static void invert_bits(ByteBuffer& decoded)
+{
+    for (u8& byte : decoded.bytes())
+        byte = ~byte;
+}
+
 PDFErrorOr<ByteBuffer> Filter::decode_ccitt(ReadonlyBytes bytes, RefPtr<DictObject> decode_parms)
 {
     // Table 3.9 Optional parameters for the CCITTFaxDecode filter
@@ -310,14 +316,21 @@ PDFErrorOr<ByteBuffer> Filter::decode_ccitt(ReadonlyBytes bytes, RefPtr<DictObje
     //        achieve to decode images that have it. Figure out what to do with it.
     (void)end_of_block;
 
-    if (require_end_of_line || encoded_byte_align || black_is_1 || damaged_rows_before_error > 0 || rows == 0)
+    if (require_end_of_line || encoded_byte_align || damaged_rows_before_error > 0 || rows == 0)
         return Error::rendering_unsupported_error("Unimplemented option for the CCITTFaxDecode Filter");
 
+    ByteBuffer decoded {};
     if (k < 0)
-        return TRY(Gfx::CCITT::decode_ccitt_group4(bytes, columns, rows));
-    if (k == 0)
+        decoded = TRY(Gfx::CCITT::decode_ccitt_group4(bytes, columns, rows));
+    else if (k == 0)
         return Error::rendering_unsupported_error("CCITTFaxDecode Filter Group 3, 1-D is unsupported");
-    return Error::rendering_unsupported_error("CCITTFaxDecode Filter Group 3, 2-D is unsupported");
+    else
+        return Error::rendering_unsupported_error("CCITTFaxDecode Filter Group 3, 2-D is unsupported");
+
+    if (!black_is_1)
+        invert_bits(decoded);
+
+    return decoded;
 }
 
 PDFErrorOr<ByteBuffer> Filter::decode_jbig2(ReadonlyBytes)