dnxhddec: use dequantization formula from specs

The current one, while correct, does not yield the best possible
results. The specificiations suggest another formula, which results
in quality gains in the decoded output from fate tests. This
justifies changing said formula.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/dnxhddec.c

@@ -357,8 +357,9 @@ static av_always_inline int dnxhd_decode_dct_block(const DNXHDContext *ctx,
 
         j     = ctx->scantable.permutated[i];
         level *= scale[i];
+        level += scale[i] >> 1;
         if (level_bias < 32 || weight_matrix[i] != level_bias)
-            level += level_bias;
+            level += level_bias; // 1<<(level_shift-1)
         level >>= level_shift;
 
         block[j] = (level ^ sign) - sign;

tests/ref/vsynth/vsynth1-dnxhd-1080i

 a0234e0a8516d958f423b119aa9e35c4 *tests/data/fate/vsynth1-dnxhd-1080i.mov
 3031911 tests/data/fate/vsynth1-dnxhd-1080i.mov
-a09132c6db44f415e831dcaa630a351b *tests/data/fate/vsynth1-dnxhd-1080i.out.rawvideo
-stddev:    6.29 PSNR: 32.15 MAXDIFF:   64 bytes:  7603200/   760320
+fed9ed2a5179c9df0ef58772b025e303 *tests/data/fate/vsynth1-dnxhd-1080i.out.rawvideo
+stddev:    6.18 PSNR: 32.31 MAXDIFF:   64 bytes:  7603200/   760320

tests/ref/vsynth/vsynth1-dnxhd-1080i-colr

 5fccdb16c0f14dea1b6b603bac90b97e *tests/data/fate/vsynth1-dnxhd-1080i-colr.mov
 3031929 tests/data/fate/vsynth1-dnxhd-1080i-colr.mov
-5835dff88cb84e83bbe70b5ed5edd5ab *tests/data/fate/vsynth1-dnxhd-1080i-colr.out.rawvideo
-stddev:    5.79 PSNR: 32.87 MAXDIFF:   56 bytes:  7603200/   760320
+6f2d5429ffc4529a76acfeb28b560542 *tests/data/fate/vsynth1-dnxhd-1080i-colr.out.rawvideo
+stddev:    5.65 PSNR: 33.09 MAXDIFF:   55 bytes:  7603200/   760320

tests/ref/vsynth/vsynth1-dnxhd-720p

 af03d57b8320568027162132643f7814 *tests/data/fate/vsynth1-dnxhd-720p.dnxhd
 2293760 tests/data/fate/vsynth1-dnxhd-720p.dnxhd
-f074f1b5ed394871b3c73184ad55b895 *tests/data/fate/vsynth1-dnxhd-720p.out.rawvideo
-stddev:    6.26 PSNR: 32.19 MAXDIFF:   65 bytes:  7603200/   760320
+5f9fba5bacda81e77a72d8a816612564 *tests/data/fate/vsynth1-dnxhd-720p.out.rawvideo
+stddev:    6.22 PSNR: 32.24 MAXDIFF:   64 bytes:  7603200/   760320

tests/ref/vsynth/vsynth1-dnxhd-720p-10bit

 f8c4b7aa165a80df2485d526161290a3 *tests/data/fate/vsynth1-dnxhd-720p-10bit.dnxhd
 2293760 tests/data/fate/vsynth1-dnxhd-720p-10bit.dnxhd
-ec26a6cbf53e38ffb9d5c51cbfbf4f7c *tests/data/fate/vsynth1-dnxhd-720p-10bit.out.rawvideo
-stddev:    6.27 PSNR: 32.18 MAXDIFF:   64 bytes:  7603200/   760320
+3cc84f9e8d2e704475b410de27dd9951 *tests/data/fate/vsynth1-dnxhd-720p-10bit.out.rawvideo
+stddev:    6.23 PSNR: 32.23 MAXDIFF:   64 bytes:  7603200/   760320

tests/ref/vsynth/vsynth1-dnxhd-720p-rd

 276e5175376051218b0e3eb36f9e9a63 *tests/data/fate/vsynth1-dnxhd-720p-rd.dnxhd
 2293760 tests/data/fate/vsynth1-dnxhd-720p-rd.dnxhd
-28662df973b289798bf6069fbbee8071 *tests/data/fate/vsynth1-dnxhd-720p-rd.out.rawvideo
-stddev:    6.26 PSNR: 32.19 MAXDIFF:   65 bytes:  7603200/   760320
+1c75ad86ccd5cc2112da7d43ace50dbf *tests/data/fate/vsynth1-dnxhd-720p-rd.out.rawvideo
+stddev:    6.23 PSNR: 32.23 MAXDIFF:   64 bytes:  7603200/   760320

tests/ref/vsynth/vsynth2-dnxhd-1080i

 2b75889122f8d918e1b068d128b618ca *tests/data/fate/vsynth2-dnxhd-1080i.mov
 3031911 tests/data/fate/vsynth2-dnxhd-1080i.mov
-099001db73036eeb9545c463cf90f0ba *tests/data/fate/vsynth2-dnxhd-1080i.out.rawvideo
-stddev:    1.53 PSNR: 44.43 MAXDIFF:   31 bytes:  7603200/   760320
+e941d2587cfeccddc450da7f41f7f911 *tests/data/fate/vsynth2-dnxhd-1080i.out.rawvideo
+stddev:    1.50 PSNR: 44.56 MAXDIFF:   31 bytes:  7603200/   760320

tests/ref/vsynth/vsynth2-dnxhd-1080i-colr

 f9827e9867b0ea4f7585d8e362a58413 *tests/data/fate/vsynth2-dnxhd-1080i-colr.mov
 3031929 tests/data/fate/vsynth2-dnxhd-1080i-colr.mov
-e4cf5528c993b5e7d57a9d0a4d2cd0c6 *tests/data/fate/vsynth2-dnxhd-1080i-colr.out.rawvideo
-stddev:    1.58 PSNR: 44.15 MAXDIFF:   33 bytes:  7603200/   760320
+ec40a8014b819d02951b2f06bee7b514 *tests/data/fate/vsynth2-dnxhd-1080i-colr.out.rawvideo
+stddev:    1.54 PSNR: 44.33 MAXDIFF:   33 bytes:  7603200/   760320

tests/ref/vsynth/vsynth2-dnxhd-720p

 3bb2d4fe12b49eae830918d68bde0675 *tests/data/fate/vsynth2-dnxhd-720p.dnxhd
 2293760 tests/data/fate/vsynth2-dnxhd-720p.dnxhd
-903e5a7f2b84c0cd362a0f3a69549989 *tests/data/fate/vsynth2-dnxhd-720p.out.rawvideo
-stddev:    1.53 PSNR: 44.41 MAXDIFF:   31 bytes:  7603200/   760320
+bf3c208086609fea7cb40a9ad97b1fd4 *tests/data/fate/vsynth2-dnxhd-720p.out.rawvideo
+stddev:    1.52 PSNR: 44.49 MAXDIFF:   31 bytes:  7603200/   760320

tests/ref/vsynth/vsynth2-dnxhd-720p-10bit

 e49cb87f69acc809aee55d64990c84a9 *tests/data/fate/vsynth2-dnxhd-720p-10bit.dnxhd
 2293760 tests/data/fate/vsynth2-dnxhd-720p-10bit.dnxhd
-3eb47758e42db9fc704e1254b7abbeb0 *tests/data/fate/vsynth2-dnxhd-720p-10bit.out.rawvideo
-stddev:    1.56 PSNR: 44.25 MAXDIFF:   31 bytes:  7603200/   760320
+a98c4b69d4d036089a455e147d6922a7 *tests/data/fate/vsynth2-dnxhd-720p-10bit.out.rawvideo
+stddev:    1.54 PSNR: 44.36 MAXDIFF:   31 bytes:  7603200/   760320

tests/ref/vsynth/vsynth2-dnxhd-720p-rd

 b723c7412a4c93f500b917ad721f6d21 *tests/data/fate/vsynth2-dnxhd-720p-rd.dnxhd
 2293760 tests/data/fate/vsynth2-dnxhd-720p-rd.dnxhd
-f7d437ea7024700cfd61c40197f44852 *tests/data/fate/vsynth2-dnxhd-720p-rd.out.rawvideo
-stddev:    1.53 PSNR: 44.40 MAXDIFF:   31 bytes:  7603200/   760320
+b7c5de5578317654792c6ea31bfeeb7d *tests/data/fate/vsynth2-dnxhd-720p-rd.out.rawvideo
+stddev:    1.52 PSNR: 44.48 MAXDIFF:   31 bytes:  7603200/   760320

tests/ref/vsynth/vsynth3-dnxhd-1080i-colr

 ee7a70832f37793b62642f770d988bdb *tests/data/fate/vsynth3-dnxhd-1080i-colr.mov
 3031929 tests/data/fate/vsynth3-dnxhd-1080i-colr.mov
-7dd6b261e439cda21df4f01b45336b41 *tests/data/fate/vsynth3-dnxhd-1080i-colr.out.rawvideo
+f907fd2d48bedbc5283fbfc3fb9f61a0 *tests/data/fate/vsynth3-dnxhd-1080i-colr.out.rawvideo
 stddev:    6.92 PSNR: 31.32 MAXDIFF:   50 bytes:    86700/     8670

tests/ref/vsynth/vsynth_lena-dnxhd-1080i

 f7412afbcb4454692f7492f6710189e3 *tests/data/fate/vsynth_lena-dnxhd-1080i.mov
 3031911 tests/data/fate/vsynth_lena-dnxhd-1080i.mov
-744ba46da5d4c19a28562ea31061d170 *tests/data/fate/vsynth_lena-dnxhd-1080i.out.rawvideo
-stddev:    1.31 PSNR: 45.77 MAXDIFF:   23 bytes:  7603200/   760320
+7d0ca92f12711535d57eff3609462b31 *tests/data/fate/vsynth_lena-dnxhd-1080i.out.rawvideo
+stddev:    1.29 PSNR: 45.87 MAXDIFF:   22 bytes:  7603200/   760320

tests/ref/vsynth/vsynth_lena-dnxhd-1080i-colr

 5ba3ddb58b10e5f0069cb4f82d594695 *tests/data/fate/vsynth_lena-dnxhd-1080i-colr.mov
 3031929 tests/data/fate/vsynth_lena-dnxhd-1080i-colr.mov
-864c3d5f49d9edf66ce8f82a2a6725f6 *tests/data/fate/vsynth_lena-dnxhd-1080i-colr.out.rawvideo
-stddev:    1.36 PSNR: 45.45 MAXDIFF:   22 bytes:  7603200/   760320
+ce4993a69ef55c8c4b18138716f17b6f *tests/data/fate/vsynth_lena-dnxhd-1080i-colr.out.rawvideo
+stddev:    1.33 PSNR: 45.59 MAXDIFF:   22 bytes:  7603200/   760320

tests/ref/vsynth/vsynth_lena-dnxhd-720p

 4ca9473a8d106bdfe36e9bf7c516b648 *tests/data/fate/vsynth_lena-dnxhd-720p.dnxhd
 2293760 tests/data/fate/vsynth_lena-dnxhd-720p.dnxhd
-d44c4b08cda8a8042ae345124fdfffcc *tests/data/fate/vsynth_lena-dnxhd-720p.out.rawvideo
-stddev:    1.32 PSNR: 45.68 MAXDIFF:   22 bytes:  7603200/   760320
+9ccd48d24b4f1af2323b65abb6d65d7f *tests/data/fate/vsynth_lena-dnxhd-720p.out.rawvideo
+stddev:    1.31 PSNR: 45.77 MAXDIFF:   22 bytes:  7603200/   760320

tests/ref/vsynth/vsynth_lena-dnxhd-720p-10bit

 e96fc4a7d994b9369c50da32fd325822 *tests/data/fate/vsynth_lena-dnxhd-720p-10bit.dnxhd
 2293760 tests/data/fate/vsynth_lena-dnxhd-720p-10bit.dnxhd
-0449440eb3e8416840a27deb1a8f80b0 *tests/data/fate/vsynth_lena-dnxhd-720p-10bit.out.rawvideo
-stddev:    1.35 PSNR: 45.47 MAXDIFF:   22 bytes:  7603200/   760320
+2b497215c57558910a605ff8c78430d9 *tests/data/fate/vsynth_lena-dnxhd-720p-10bit.out.rawvideo
+stddev:    1.33 PSNR: 45.61 MAXDIFF:   22 bytes:  7603200/   760320

tests/ref/vsynth/vsynth_lena-dnxhd-720p-rd

 b305b03708e905717b42fc0b304367d4 *tests/data/fate/vsynth_lena-dnxhd-720p-rd.dnxhd
 2293760 tests/data/fate/vsynth_lena-dnxhd-720p-rd.dnxhd
-13de1c5ed025abb5120450e134aa623d *tests/data/fate/vsynth_lena-dnxhd-720p-rd.out.rawvideo
-stddev:    1.32 PSNR: 45.66 MAXDIFF:   22 bytes:  7603200/   760320
+3793391df8448937b17d876b6df0d26d *tests/data/fate/vsynth_lena-dnxhd-720p-rd.out.rawvideo
+stddev:    1.31 PSNR: 45.75 MAXDIFF:   22 bytes:  7603200/   760320