update to latest metadata schema

tensorflow/lite/micro/compression.h

@@ -26,7 +26,8 @@ namespace tflite {
 // Compressed tensors
 //
 
-static constexpr const char* kCompressionMetadataString = "TFLM_COMPRESSION";
+static constexpr const char* kCompressionMetadataString =
+    "COMPRESSION_METADATA";
 
 enum class CompressionScheme : uint8_t {
   kBinQuant,

tensorflow/lite/micro/compression/BUILD

@@ -13,11 +13,6 @@ flatbuffer_cc_library(
     srcs = ["metadata.fbs"],
 )
 
-flatbuffer_py_library(
-    name = "original_flatbuffer_py",
-    srcs = ["original.fbs"],
-)
-
 flatbuffer_py_library(
     name = "metadata_flatbuffer_py",
     srcs = ["metadata.fbs"],
@@ -34,33 +29,6 @@ cc_test(
     size = "small",
 )
 
-py_binary(
-    name = "compress",
-    srcs = ["compress.py"],
-    deps = [
-        "@absl_py//absl:app",
-        "@absl_py//absl/flags",
-        "@absl_py//absl/logging",
-        "@flatbuffers//:runtime_py",
-        "metadata_flatbuffer_py",
-        "//tensorflow/lite/python:schema_py",
-        requirement("bitarray"),
-        requirement("numpy"),
-        requirement("scikit-learn"),
-    ],
-)
-
-py_binary(
-    name = "view",
-    srcs = [
-        "view.py",
-    ],
-    deps = [
-        "metadata_flatbuffer_py",
-        "//tensorflow/lite/python:schema_py",
-    ],
-)
-
 py_test(
     name = "metadata_test_py",
     main = "metadata_test.py",
@@ -72,23 +40,3 @@ py_test(
     ],
     size = "small",
 )
-
-py_test(
-    name = "original_test_py",
-    main = "original_test.py",
-    srcs = ["original_test.py"],
-    deps = [
-        "original_flatbuffer_py",
-        "@flatbuffers//:runtime_py",
-        requirement("hexdump"),
-    ],
-    size = "small",
-)
-
-genrule(
-    name = "hello_world_int8.compressed",
-    srcs = ["//tensorflow/lite/micro/examples/hello_world/models:hello_world_int8.tflite"],
-    outs = ["hello_world_int8.compressed.tflite"],
-    cmd = "$(location :compress) --input_model_path $< --output_model_path $@",
-    tools = [":compress"],
-)

tensorflow/lite/micro/compression/metadata.fbs

@@ -12,27 +12,38 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Flatbuffer schema describing a TFLM compressed model. Use as the value for
-// the key "TFLM_COMPRESSION" in the metadata table in a .tflite flatbuffer.
-
 namespace tflite.micro.compression;
 
 table Metadata {
-    lut_tensors:[LutTensor];  // list of tensors that are compressed by LUT
+    // Compression data root, to be used in a tflite.Model.metadata field with
+    // the key "COMPRESSION_METADATA".
+
+    subgraphs:[Subgraph];  // compression data indexed by subgraph index
+}
+
+table Subgraph {
+    // Per-subgraph compression metadata.
+
+    lut_tensors:[LutTensor];
+        // ^ A list of tensors which are compressed using the
+        // (L)ook-(U)p-(T)able method. The indices of this vector are not
+        // significant.
 }
 
-struct LutTensor {
-    subgraph:uint16;       // the index of the subgraph
-    tensor:uint16;         // the index of the tensor in its subgraph
-    index_bitwidth:uint8;  // the bit-width of LUT indexes
-    index_buffer:uint16;   // the index of the buffer containing LUT indexes
-    value_buffer:uint16;   // the index of the buffer containing LUT values
+table LutTensor {
+    // Look-Up-Table Tensor: a tensor representation where elements are
+    // compressed into indices into a table of values. The indices are unsigned
+    // integers, index_bitwidth-wide, in big-endian bit order, packed into the
+    // buffer identified by the corresponding tflite.Tensor's buffer field. The
+    // values are located in a newly-created buffer, encoded according to the
+    // tflite.Tensor.type. Tensors with multiple channels have distinct values
+    // tables for each channel, concatenated one after another in the buffer.
+    // An element's LUT index must be looked up in the value table for its
+    // channel.
+
+    tensor:int;            // index of the corresponding tflite.Tensor
+    value_buffer:uint;     // index of the buffer containing LUT values
+    index_bitwidth:uint8;  // bit-width of LUT indexes
 }
-// Look-Up-Table tensors are encoded in two buffers: an index buffer and a
-// value buffer. The indexes are unsigned integers packed into the index buffer
-// in bitwidth-wide bit fields with a big-endian bit order. The data in the
-// value buffer is encoded as usual according to the type of the tensor.
-// Tensors with multiple channels have distinct values tables for each channel,
-// concatinated into one value buffer. (Will elaborate this comment.)
 
 root_type Metadata;