diff --git a/plugins/ImageReader/ImageReader.py b/plugins/ImageReader/ImageReader.py
index 2084844548..a77cc9b0ed 100644
--- a/plugins/ImageReader/ImageReader.py
+++ b/plugins/ImageReader/ImageReader.py
@@ -108,7 +108,7 @@ class ImageReader(MeshReader):
 
         Job.yieldThread()
 
-        if lighter_is_higher is use_transparency_model:
+        if lighter_is_higher == use_transparency_model:
             height_data = 1 - height_data
 
         for _ in range(0, blur_iterations):
@@ -129,11 +129,11 @@ class ImageReader(MeshReader):
             Job.yieldThread()
 
         if use_transparency_model:
-            p = 1.0 / math.log(transmittance_1mm / 100.0, 2)
+            p = 1.0 / math.log(transmittance_1mm / 100.0, 2) # base doesn't matter here. use base 2 for fast computation
             min_luminance = 2.0 ** ((peak_height - base_height) / p)
             for (y, x) in numpy.ndindex(height_data.shape):
                 mapped_luminance = min_luminance + (1.0 - min_luminance) * height_data[y, x]
-                height_data[y, x] = base_height + p * math.log(mapped_luminance, 2)
+                height_data[y, x] = base_height + p * math.log(mapped_luminance, 2) # use same base as a couple lines above this
         else:
             height_data *= scale_vector.y
             height_data += base_height