had a change of mind: issue a warning when encountering negative values, but then just clamp them and continue rendering (rather than failing)

include/mitsuba/render/mipmap.h

@@ -219,6 +219,17 @@ public:
 
 		m_pyramid[0].cleanup();
 		m_pyramid[0].init((Value *) bitmap->getData(), m_minimum, m_maximum, m_average);
+
+		if (m_minimum.min() < 0) {
+			Log(EWarn, "The texture contains negative pixel values! These will be clamped!");
+			Value *value = (Value *) bitmap->getData();
+
+			for (size_t i=0, count=bitmap->getPixelCount(); i<count; ++i) 
+				(*value++).clampNegative();
+
+			m_pyramid[0].init((Value *) bitmap->getData(), m_minimum, m_maximum, m_average);
+		}
+
 		m_sizeRatio[0] = Vector2(1, 1);
 
 		/* 3. Progressively downsample until only a 1x1 image is left */

src/emitters/envmap.cpp

@@ -181,10 +181,6 @@ public:
 				std::numeric_limits<Float>::infinity(), Spectrum::EIlluminant);
 		}
 
-		if (m_mipmap->getMinimum().min() < 0)
-			Log(EError, "\"%s\": The environment map contains negative pixel values! This is not allowed.",
-				m_filename.string().c_str());
-
 		if (props.hasProperty("intensityScale"))
 			Log(EError, "The 'intensityScale' parameter has been deprecated and is now called scale.");
 

src/textures/bitmap.cpp

@@ -277,11 +277,6 @@ public:
 					rfilter, m_wrapModeU, m_wrapModeV, m_filterType, m_maxAnisotropy, 
 					createCache ? cacheFile : fs::path(), timestamp);
 		}
-
-		if ((m_mipmap1 && m_mipmap1->getMinimum().min() < 0) ||
-		    (m_mipmap3 && m_mipmap3->getMinimum().min() < 0))
-			Log(EError, "\"%s\": The texture map contains negative pixel values! This is not allowed.",
-				m_filename.string().c_str());
 	}
 
 	inline ReconstructionFilter::EBoundaryCondition parseWrapMode(const std::string &wrapMode) {