add simd code when scn equals 4 at Lab2RGB_b().

modules/imgproc/src/color.cpp

@@ -5464,6 +5464,7 @@ struct Lab2RGB_b
         v_128 = vdupq_n_f32(128.0f);
         #elif CV_SSE2
         v_scale = _mm_set1_ps(255.f);
+        v_alpha = _mm_set1_ps(ColorChannel<uchar>::max());
         v_zero = _mm_setzero_si128();
         haveSIMD = checkHardwareSupport(CV_CPU_SSE2);
         #endif
@@ -5621,6 +5622,32 @@ struct Lab2RGB_b
                 if (jr)
                     dst -= jr, j -= jr;
             }
+            else if (dcn == 4 && haveSIMD)
+            {
+                for ( ; j <= (dn * 3 - 12); j += 12, dst += 16)
+                {
+                    __m128 v_buf0 = _mm_mul_ps(_mm_load_ps(buf + j), v_scale);
+                    __m128 v_buf1 = _mm_mul_ps(_mm_load_ps(buf + j + 4), v_scale);
+                    __m128 v_buf2 = _mm_mul_ps(_mm_load_ps(buf + j + 8), v_scale);
+
+                    __m128 v_ba0 = _mm_unpackhi_ps(v_buf0, v_alpha);
+                    __m128 v_ba1 = _mm_unpacklo_ps(v_buf2, v_alpha);
+
+                    __m128i v_src0 = _mm_cvtps_epi32(_mm_shuffle_ps(v_buf0, v_ba0, 0x44));
+                    __m128i v_src1 = _mm_shuffle_epi32(_mm_cvtps_epi32(_mm_shuffle_ps(v_ba0, v_buf1, 0x4e)), 0x78);
+                    __m128i v_src2 = _mm_cvtps_epi32(_mm_shuffle_ps(v_buf1, v_ba1, 0x4e));
+                    __m128i v_src3 = _mm_shuffle_epi32(_mm_cvtps_epi32(_mm_shuffle_ps(v_ba1, v_buf2, 0xee)), 0x78);
+
+                    __m128i v_dst0 = _mm_packs_epi32(v_src0, v_src1);
+                    __m128i v_dst1 = _mm_packs_epi32(v_src2, v_src3);
+
+                    _mm_storeu_si128((__m128i *)dst, _mm_packus_epi16(v_dst0, v_dst1));
+                }
+
+                int jr = j % 3;
+                if (jr)
+                    dst -= jr, j -= jr;
+            }
             #endif
 
             for( ; j < dn*3; j += 3, dst += dcn )
@@ -5642,6 +5669,7 @@ struct Lab2RGB_b
     uint8x8_t v_alpha;
     #elif CV_SSE2
     __m128 v_scale;
+    __m128 v_alpha;
     __m128i v_zero;
     bool haveSIMD;
     #endif