fix diffusion

diff --git a/s2tc_compressor.cpp b/s2tc_compressor.cpp
index bcdb1fe..c6ad8ec 100644 (file)
--- a/s2tc_compressor.cpp
+++ b/s2tc_compressor.cpp
@@ -720,7 +720,7 @@ namespace
                int ret = max(0, min(src >> shift, maxval));
                // simulate decoding ("loop filter")
                int loop = (ret << shift) | (ret >> (8 - 2 * shift));
-               *diff = loop - ret;
+               *diff = src - loop;
                return ret;
        }
 };