From 760e4ebc9d89edb274cf6578f152a04ae4fb0566 Mon Sep 17 00:00:00 2001
From: Marcos Del Sol Vives <marcos@orca.pet>
Date: Sun, 7 Jan 2024 20:32:31 +0100
Subject: [PATCH] Increase precision in color matching

---
 client/src/imgutils.c | 33 ++++++++++++++++++---------------
 tools/pm3_tests.sh    |  2 +-
 2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/client/src/imgutils.c b/client/src/imgutils.c
index 1ebcddbb6..a58a5b29a 100644
--- a/client/src/imgutils.c
+++ b/client/src/imgutils.c
@@ -64,6 +64,9 @@ gdImagePtr img_palettize(gdImagePtr rgb, int * palette, int palette_size) {
      *
      * Note that we are storing two extra values so we don't have to do boundary checking at
      * the left and right edges of the image.
+     *
+     * To reduce shifts and increase accuracy, each entry is stored with 16x times the error,
+     * and gets divided by that amount when it is read.
      */
     struct ycbcr_t * forward = calloc(gdImageSX(rgb) + 2, sizeof(struct ycbcr_t));
     if (!forward) {
@@ -89,9 +92,9 @@ gdImagePtr img_palettize(gdImagePtr rgb, int * palette, int palette_size) {
             rgb_to_ycbcr(gdImageGetTrueColorPixel(rgb, x, y), &pix);
 
             // Add error for current pixel
-            pix.y  += row_err.y;
-            pix.cb += row_err.cb;
-            pix.cr += row_err.cr;
+            pix.y  += row_err.y  / 16;
+            pix.cb += row_err.cb / 16;
+            pix.cr += row_err.cr / 16;
 
             // Cap in case it went to imaginary color territory
             cap_comp(&pix.y);
@@ -129,24 +132,24 @@ gdImagePtr img_palettize(gdImagePtr rgb, int * palette, int palette_size) {
             gdImageSetPixel(res, x, y, best_idx);
 
             // Propagate error within the current row, to the pixel to the right
-            row_err.y  = best_err.y  * 7 / 16 + forward[x + 2].y;
-            row_err.cb = best_err.cb * 7 / 16 + forward[x + 2].cb;
-            row_err.cr = best_err.cr * 7 / 16 + forward[x + 2].cr;
+            row_err.y  = best_err.y  * 7 + forward[x + 2].y;
+            row_err.cb = best_err.cb * 7 + forward[x + 2].cb;
+            row_err.cr = best_err.cr * 7 + forward[x + 2].cr;
 
             // Add error to bottom left
-            forward[x + 0].y  += best_err.y  * 3 / 16;
-            forward[x + 0].cb += best_err.cb * 3 / 16;
-            forward[x + 0].cr += best_err.cr * 3 / 16;
+            forward[x + 0].y  += best_err.y  * 3;
+            forward[x + 0].cb += best_err.cb * 3;
+            forward[x + 0].cr += best_err.cr * 3;
 
             // Add error to bottom center
-            forward[x + 1].y  += best_err.y  * 5 / 16;
-            forward[x + 1].cb += best_err.cb * 5 / 16;
-            forward[x + 1].cr += best_err.cr * 5 / 16;
+            forward[x + 1].y  += best_err.y  * 5;
+            forward[x + 1].cb += best_err.cb * 5;
+            forward[x + 1].cr += best_err.cr * 5;
 
             // Set error to bottom right
-            forward[x + 2].y   = best_err.y  * 1 / 16;
-            forward[x + 2].cb  = best_err.cb * 1 / 16;
-            forward[x + 2].cr  = best_err.cr * 1 / 16;
+            forward[x + 2].y   = best_err.y  * 1;
+            forward[x + 2].cb  = best_err.cb * 1;
+            forward[x + 2].cr  = best_err.cr * 1;
         }
     }
 
diff --git a/tools/pm3_tests.sh b/tools/pm3_tests.sh
index 2e32b39bb..e1d574738 100755
--- a/tools/pm3_tests.sh
+++ b/tools/pm3_tests.sh
@@ -535,7 +535,7 @@ while true; do
       if ! CheckExecute "emv test"                       "$CLIENTBIN -c 'emv test'" "Test\(s\) \[ ok"; then break; fi
       if ! CheckExecute "hf cipurse test"                "$CLIENTBIN -c 'hf cipurse test'" "Tests \[ ok"; then break; fi
       if ! CheckExecute "hf mfdes test"                  "$CLIENTBIN -c 'hf mfdes test'"   "Tests \[ ok"; then break; fi
-      if ! CheckExecute "hf waveshare load"              "$CLIENTBIN -c 'hf waveshare load -m 6 -f tools/lena.bmp -s dither.bmp' && echo '9cee7dcc285f59f88c7cbc9de1dc02b4 dither.bmp' | md5sum -c" "dither.bmp: OK"; then break; fi
+      if ! CheckExecute "hf waveshare load"              "$CLIENTBIN -c 'hf waveshare load -m 6 -f tools/lena.bmp -s dither.bmp' && echo '34ff55fe7257876acf30dae00eb0e439 dither.bmp' | md5sum -c" "dither.bmp: OK"; then break; fi
     fi
   echo -e "\n------------------------------------------------------------"
   echo -e "Tests [ ${C_GREEN}OK${C_NC} ] ${C_OK}\n"