From 03efc48bc51e00c0bf34bb3bb7b0311ab1ff925f Mon Sep 17 00:00:00 2001
From: Alberto Griggio <agriggio@users.noreply.github.com>
Date: Thu, 5 Apr 2018 11:22:19 +0200
Subject: [PATCH] tentative fix for #4481

---
 rtengine/ipsharpen.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/rtengine/ipsharpen.cc b/rtengine/ipsharpen.cc
index 37780c37c..505dd5db9 100644
--- a/rtengine/ipsharpen.cc
+++ b/rtengine/ipsharpen.cc
@@ -106,7 +106,7 @@ void ImProcFunctions::deconvsharpening (float** luminance, float** tmp, int W, i
 
     for (int i = 0; i < H; i++) {
         for(int j = 0; j < W; j++) {
-            tmpI[i][j] = luminance[i][j];
+            tmpI[i][j] = max(luminance[i][j], 0.f);
         }
     }
 
@@ -122,6 +122,11 @@ void ImProcFunctions::deconvsharpening (float** luminance, float** tmp, int W, i
             if (!needdamp) {
                 // apply gaussian blur and divide luminance by result of gaussian blur
                 gaussianBlur (tmpI, tmp, W, H, sigma, nullptr, GAUSS_DIV, luminance);
+                for (int i = 0; i < H; i++) {
+                    for(int j = 0; j < W; j++) {
+                        tmp[i][j] = max(tmp[i][j], 0.f);
+                    }
+                }
             } else {
                 // apply gaussian blur + damping
                 gaussianBlur (tmpI, tmp, W, H, sigma);