fix(compare_Yee): Access correct channel in GaussianPyramid

The GaussianPyramid::value() function was accessing channel 1 instead
of channel 0 when reading luminance values. Since the luminance image
(aLum/bLum) is a single-channel image extracted from the Y component
of XYZ, we need to access channel 0.

This bug caused compare_Yee to always read zeros from the pyramid,
making it unable to detect any differences between images, including
when images have different dimensions.

Fixes #4948

Signed-off-by: pmady <[email protected]>

Author: pmady

src/libOpenImageIO/imagebufalgo_yee.cpp

@@ -52,7 +52,7 @@ class GaussianPyramid {
         if (lev >= PYRAMID_MAX_LEVELS)
             return 0.0f;
         else
-            return level[lev].getchannel(x, y, 0, 1);
+            return level[lev].getchannel(x, y, 0, 0);
     }
 
 #if 0 /* unused */
@@ -65,7 +65,7 @@ class GaussianPyramid {
     float operator()(int x, int y, int lev) const
     {
         OIIO_DASSERT(lev < PYRAMID_MAX_LEVELS);
-        return level[lev].getchannel(x, y, 0, 1);
+        return level[lev].getchannel(x, y, 0, 0);
     }
 #endif