improve block extraction

bob/learn/tensorflow/dataset/__init__.py

@@ -329,18 +329,12 @@ def blocks_tensorflow(images, block_size):
     block_size = [1] + list(block_size) + [1]
     output_size = list(block_size)
     output_size[0] = -1
-    # extract image patches for each color space:
-    output = []
-    for i in range(3):
-        blocks = tf.extract_image_patches(
-            images[:, :, :, i : i + 1], block_size, block_size, [1, 1, 1, 1], "VALID"
-        )
-        if i == 0:
-            n_blocks = int(numpy.prod(blocks.shape[1:3]))
-        blocks = tf.reshape(blocks, output_size)
-        output.append(blocks)
-    # concatenate the colors back
-    output = tf.concat(output, axis=3)
+    output_size[-1] = images.shape[-1]
+    blocks = tf.extract_image_patches(
+        images, block_size, block_size, [1, 1, 1, 1], "VALID"
+    )
+    n_blocks = int(numpy.prod(blocks.shape[1:3]))
+    output = tf.reshape(blocks, output_size)
     return output, n_blocks