Use a minimum of 256 entries when computing the inverse lut
This fixes a problem reported at https://bugzilla.mozilla.org/show_bug.cgi?id=497363
diff --git a/transform.c b/transform.c
index 146f9e4..6ba0ef7 100644
--- a/transform.c
+++ b/transform.c
@@ -1364,10 +1364,17 @@
} else if (trc->count == 1) {
compute_precache_pow(output, 1./u8Fixed8Number_to_float(trc->data[0]));
} else {
- uint16_t *inverted = invert_lut(trc->data, trc->count, trc->count);
+ uint16_t *inverted;
+ int inverted_size = trc->count;
+ //XXX: the choice of a minimum of 256 here is not backed by any theory, measurement or data, however it is what lcms uses.
+ // the maximum number we would need is 65535 because that's the accuracy used for computing the precache table
+ if (inverted_size < 256)
+ inverted_size = 256;
+
+ inverted = invert_lut(trc->data, trc->count, inverted_size);
if (!inverted)
return false;
- compute_precache_lut(output, inverted, trc->count);
+ compute_precache_lut(output, inverted, inverted_size);
free(inverted);
}
return true;
@@ -1442,7 +1449,6 @@
return false;
}
-
void build_output_lut(struct curveType *trc,
uint16_t **output_gamma_lut, size_t *output_gamma_lut_length)
{
@@ -1454,8 +1460,12 @@
*output_gamma_lut = build_pow_table(gamma, 4096);
*output_gamma_lut_length = 4096;
} else {
- *output_gamma_lut = invert_lut(trc->data, trc->count, trc->count);
+ //XXX: the choice of a minimum of 256 here is not backed by any theory, 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);
}
}
