test: fix a bug with naive offset

antecedent/jpeg_toolbox.py

@@ -218,8 +218,8 @@ def jpeg_idct_naive(blocks: np.ndarray, quant_tbl: np.ndarray) -> np.ndarray:
 
     Returns: an array with the same shape as blocks with DCT values.
     """
-    blocks = blocks.astype(float) + 128
-    return idctn(blocks * quant_tbl.astype(np.uint16), axes=(-2, -1), norm='ortho')
+    blocks = blocks.astype(float)
+    return idctn(blocks * quant_tbl.astype(np.uint16), axes=(-2, -1), norm='ortho') + 128
 
 
 def jpeg_idct_islow(blocks: np.ndarray, quant_tbl: np.ndarray) -> np.ndarray:

test/test_jpeg_toolbox.py

 import numpy as np
 import unittest
 from antecedent.jpeg_toolbox import llm_dct_islow, jpeg_fdct_islow, define_quant_table, quality_scaling_law, \
-    quantize_islow_fdct
+    quantize_islow_fdct, jpeg_fdct_naive, jpeg_idct_naive, jpeg_idct_islow
 
 
 class TestJPEGToolbox(unittest.TestCase):
@@ -67,3 +67,10 @@ class TestJPEGToolbox(unittest.TestCase):
                                                  quantize_islow_fdct(split_blocks[2], chrominance)],
                                                 axis=1)
         self.assertTrue(np.allclose(quantized_blocks, split_quantized_blocks))
+
+    def test_naive_dct_inversion(self):
+        quant_tbl = np.ones((8,8), dtype=np.uint16)
+        blocks = np.random.randint(0, 256, size=(1, 1, 8, 8), dtype=np.int32)
+        dct = jpeg_fdct_naive(blocks)
+        spatial = jpeg_idct_naive(dct, quant_tbl=quant_tbl)
+        self.assertTrue(np.allclose(spatial, blocks))
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