Fix dithering bug in merged 4:2:0/RGB565 algorithm

d0 should always be used for the first row, and d1 should always be used
for the second row.

Addresses concerns raised in #95, #81.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 46094cc84b050c25b0867cfa9e528ef2b7479be9..296e408ba254b845ad19e01fe41f54c9a6088fb2 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -455,7 +455,7 @@ else()
   set(MD5_BMP_420_ISLOW_565 bf9d13e16c4923b92e1faa604d7922cb)
   set(MD5_BMP_420_ISLOW_565D 6bde71526acc44bcff76f696df8638d2)
   set(MD5_BMP_420M_ISLOW_565 8dc0185245353cfa32ad97027342216f)
-  set(MD5_BMP_420M_ISLOW_565D d1be3a3339166255e76fa50a0d70d73e)
+  set(MD5_BMP_420M_ISLOW_565D ce034037d212bc403330df6f915c161b)
   set(MD5_PPM_420_ISLOW_SKIP15_31 c4c65c1e43d7275cd50328a61e6534f0)
   set(MD5_PPM_420_ISLOW_ARI_SKIP16_139 087c6b123db16ac00cb88c5b590bb74a)
   set(MD5_PPM_420_ISLOW_PROG_CROP62x62_71_71 26eb36ccc7d1f0cb80cdabb0ac8b5d99)

diff --git a/ChangeLog.md b/ChangeLog.md
index e44ddc899f58c37658f2bffb97401ce6fe7c83ac..406c6db272c4ec78cc8d225f5bf2c2420e18202e 100644 (file)
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -7,6 +7,10 @@ to decompress a specially-crafted malformed JPEG image.  These issues did not
 pose a security threat, but removing the warnings makes it easier to detect
 actual security issues, should they arise in the future.
 
+2. Fixed a bug in the merged 4:2:0 upsampling/dithered RGB565 color conversion
+algorithm that caused incorrect dithering in the output image.  This algorithm
+now produces bitwise-identical results to the unmerged algorithms.
+
 
 1.5.3
 =====

diff --git a/Makefile.am b/Makefile.am
index 0c2d25346a6ef259bf95e045aed4df3facb571ad..1d3d42049716ec27f20f1541a67eeef1d6e83bd6 100644 (file)
--- a/Makefile.am
+++ b/Makefile.am
@@ -275,7 +275,7 @@ MD5_BMP_420_ISLOW_256 = 4980185e3776e89bd931736e1cddeee6
 MD5_BMP_420_ISLOW_565 = bf9d13e16c4923b92e1faa604d7922cb
 MD5_BMP_420_ISLOW_565D = 6bde71526acc44bcff76f696df8638d2
 MD5_BMP_420M_ISLOW_565 = 8dc0185245353cfa32ad97027342216f
-MD5_BMP_420M_ISLOW_565D =d1be3a3339166255e76fa50a0d70d73e
+MD5_BMP_420M_ISLOW_565D = ce034037d212bc403330df6f915c161b
 MD5_PPM_420_ISLOW_SKIP15_31 = c4c65c1e43d7275cd50328a61e6534f0
 MD5_PPM_420_ISLOW_ARI_SKIP16_139 = 087c6b123db16ac00cb88c5b590bb74a
 MD5_PPM_420_ISLOW_PROG_CROP62x62_71_71 = 26eb36ccc7d1f0cb80cdabb0ac8b5d99

diff --git a/jdmrg565.c b/jdmrg565.c
index 18287b373577e2058d46ede436409051bc1e4e39..a376340142816dd5755a90ade1c9ea691bb5d2e3 100644 (file)
--- a/jdmrg565.c
+++ b/jdmrg565.c
@@ -5,7 +5,7 @@
  * Copyright (C) 1994-1996, Thomas G. Lane.
  * libjpeg-turbo Modifications:
  * Copyright (C) 2013, Linaro Limited.
- * Copyright (C) 2014-2015, D. R. Commander.
+ * Copyright (C) 2014-2015, 2018, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -304,20 +304,20 @@ h2v2_merged_upsample_565D_internal (j_decompress_ptr cinfo,
     rgb = PACK_SHORT_565(r, g, b);
 
     y  = GETJSAMPLE(*inptr00++);
-    r = range_limit[DITHER_565_R(y + cred, d1)];
-    g = range_limit[DITHER_565_G(y + cgreen, d1)];
-    b = range_limit[DITHER_565_B(y + cblue, d1)];
-    d1 = DITHER_ROTATE(d1);
+    r = range_limit[DITHER_565_R(y + cred, d0)];
+    g = range_limit[DITHER_565_G(y + cgreen, d0)];
+    b = range_limit[DITHER_565_B(y + cblue, d0)];
+    d0 = DITHER_ROTATE(d0);
     rgb = PACK_TWO_PIXELS(rgb, PACK_SHORT_565(r, g, b));
 
     WRITE_TWO_PIXELS(outptr0, rgb);
     outptr0 += 4;
 
     y  = GETJSAMPLE(*inptr01++);
-    r = range_limit[DITHER_565_R(y + cred, d0)];
-    g = range_limit[DITHER_565_G(y + cgreen, d0)];
-    b = range_limit[DITHER_565_B(y + cblue, d0)];
-    d0 = DITHER_ROTATE(d0);
+    r = range_limit[DITHER_565_R(y + cred, d1)];
+    g = range_limit[DITHER_565_G(y + cgreen, d1)];
+    b = range_limit[DITHER_565_B(y + cblue, d1)];
+    d1 = DITHER_ROTATE(d1);
     rgb = PACK_SHORT_565(r, g, b);
 
     y  = GETJSAMPLE(*inptr01++);