fix(png): round dpi resolution to nearest 0.1 (#4347)

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/png.imageio/png_pvt.h

@@ -303,15 +303,22 @@ read_info(png_structp& sp, png_infop& ip, int& bit_depth, int& color_type,
     int unit;
     png_uint_32 resx, resy;
     if (png_get_pHYs(sp, ip, &resx, &resy, &unit)) {
-        float scale = 1;
         if (unit == PNG_RESOLUTION_METER) {
             // Convert to inches, to match most other formats
-            scale = 2.54 / 100.0;
+            float scale = 2.54f / 100.0f;
+            float rx    = resx * scale;
+            float ry    = resy * scale;
+            // Round to nearest 0.1
+            rx = std::round(10.0f * rx) / 10.0f;
+            ry = std::round(10.0f * ry) / 10.0f;
             spec.attribute("ResolutionUnit", "inch");
-        } else
+            spec.attribute("XResolution", rx);
+            spec.attribute("YResolution", ry);
+        } else {
             spec.attribute("ResolutionUnit", "none");
-        spec.attribute("XResolution", (float)resx * scale);
-        spec.attribute("YResolution", (float)resy * scale);
+            spec.attribute("XResolution", (float)resx);
+            spec.attribute("YResolution", (float)resy);
+        }
     }
 
     float aspect = (float)png_get_pixel_aspect_ratio(sp, ip);

testsuite/png/ref/out-libpng15.txt

@@ -5,8 +5,8 @@ Reading ../oiio-images/oiio-logo-no-alpha.png
     Comment: "Created with GIMP"
     DateTime: "2009:03:26 17:19:47"
     ResolutionUnit: "inch"
-    XResolution: 72.009
-    YResolution: 72.009
+    XResolution: 72
+    YResolution: 72
     oiio:ColorSpace: "sRGB"
 Comparing "../oiio-images/oiio-logo-no-alpha.png" and "oiio-logo-no-alpha.png"
 PASS
@@ -17,8 +17,8 @@ Reading ../oiio-images/oiio-logo-with-alpha.png
     Comment: "Created with GIMP"
     DateTime: "2009:03:26 18:44:26"
     ResolutionUnit: "inch"
-    XResolution: 72.009
-    YResolution: 72.009
+    XResolution: 72
+    YResolution: 72
     oiio:ColorSpace: "sRGB"
 Comparing "../oiio-images/oiio-logo-with-alpha.png" and "oiio-logo-with-alpha.png"
 PASS
@@ -31,8 +31,8 @@ exif.png             :   64 x   64, 3 channel, uint8 png
     channel list: R, G, B, A
     ResolutionUnit: "inch"
     Software: "OpenImageIO 2.4.1.1dev : oiiotool -no-autopremult SLEEP_MM.png -cut 1x1+227+1211 -o kaka.png"
-    XResolution: 299.999
-    YResolution: 299.999
+    XResolution: 300
+    YResolution: 300
     Exif:ImageHistory: "oiiotool -no-autopremult SLEEP_MM.png -cut 1x1+227+1211 -o kaka.png"
     oiio:ColorSpace: "Gamma2.2"
     oiio:Gamma: 2.2

testsuite/png/ref/out.txt

@@ -5,8 +5,8 @@ Reading ../oiio-images/oiio-logo-no-alpha.png
     Comment: "Created with GIMP"
     DateTime: "2009:03:26 17:19:47"
     ResolutionUnit: "inch"
-    XResolution: 72.009
-    YResolution: 72.009
+    XResolution: 72
+    YResolution: 72
     oiio:ColorSpace: "sRGB"
 Comparing "../oiio-images/oiio-logo-no-alpha.png" and "oiio-logo-no-alpha.png"
 PASS
@@ -17,8 +17,8 @@ Reading ../oiio-images/oiio-logo-with-alpha.png
     Comment: "Created with GIMP"
     DateTime: "2009:03:26 18:44:26"
     ResolutionUnit: "inch"
-    XResolution: 72.009
-    YResolution: 72.009
+    XResolution: 72
+    YResolution: 72
     oiio:ColorSpace: "sRGB"
 Comparing "../oiio-images/oiio-logo-with-alpha.png" and "oiio-logo-with-alpha.png"
 PASS
@@ -35,8 +35,8 @@ exif.png             :   64 x   64, 3 channel, uint8 png
     channel list: R, G, B, A
     ResolutionUnit: "inch"
     Software: "OpenImageIO 2.4.1.1dev : oiiotool -no-autopremult SLEEP_MM.png -cut 1x1+227+1211 -o kaka.png"
-    XResolution: 299.999
-    YResolution: 299.999
+    XResolution: 300
+    YResolution: 300
     Exif:ImageHistory: "oiiotool -no-autopremult SLEEP_MM.png -cut 1x1+227+1211 -o kaka.png"
     oiio:ColorSpace: "Gamma2.2"
     oiio:Gamma: 2.2