[qcms] lut_inverse_interp16: fix black level inversion error

third_party/qcms/src/transform_util.c

 //  qcms
 //  Copyright (C) 2009 Mozilla Foundation
 //
 // Permission is hereby granted, free of charge, to any person obtaining
 // a copy of this software and associated documentation files (the "Software"),
 // to deal in the Software without restriction, including without limitation
 // the rights to use, copy, modify, merge, publish, distribute, sublicense,
 // and/or sell copies of the Software, and to permit persons to whom the Software
 // is furnished to do so, subject to the following conditions:
 //
@@ skipping 342 matching lines @@
                     r = 0x10000;
 
                 // If the search range is inverted due to degeneracy,
                 // deem LutTable non-invertible in this search range.
                 // Refer to https://bugzil.la/1132467
 
                 if (r <= l)
                     return 0;
         }
 
+        // For input 0, return that to maintain black level. Note the binary search
+        // does not. For example, it inverts the standard sRGB gamma curve to 7 at
+        // the origin, causing a black level error.
+
+        if (Value == 0 && NumZeroes) {
+            return 0;
+        }
+
         // Seems not a degenerated case... apply binary search
 
         while (r > l) {
 
                 x = (l + r) / 2;
 
                 res = (int) lut_interp_linear16((uint16_fract_t) (x-1), LutTable, length);
 
                 if (res == Value) {
 
@@ skipping 216 matching lines @@
                         //     measurement or data, however it is what lcms uses.
                         *output_gamma_lut_length = trc->count;
                         if (*output_gamma_lut_length < 256)
                                 *output_gamma_lut_length = 256;
 
                         *output_gamma_lut = invert_lut(trc->data, trc->count, *output_gamma_lut_length);
                 }
         }
 
 }