ICC not embedded when writing PNG files

[Beep6581]

RawTherapee does not embed the ICC profile when writing PNG files!

Output profile: ACES

If I insert the ACES profile into the PNG using ExifTool then it displays correctly when using @agriggio's patch from #4260:

exiftool -ICC_Profile'<='$HOME/programs/code-rawtherapee/rtdata/iccprofiles/output/ACES.icc /tmp/colorspace_flowers\ aces.png

This is the full metadata output of PNG files produced by RawTherapee:

-ExifTool:ExifToolVersion=10.64
-System:FileName=colorspace_flowers rt_large_g10.png
-System:Directory=/tmp
-System:FileSize=2.7 MB
-System:FileModifyDate=2017:12:27 17:56:46+01:00
-System:FileAccessDate=2017:12:27 17:57:56+01:00
-System:FileInodeChangeDate=2017:12:27 17:56:46+01:00
-System:FilePermissions=rw-r--r--
-PNG:FileType=PNG
-PNG:FileTypeExtension=png
-PNG:MIMEType=image/png
-PNG-ImageHeader:ImageWidth=900
-PNG-ImageHeader:ImageHeight=604
-PNG-ImageHeader:BitDepth=16
-PNG-ImageHeader:ColorType=RGB
-PNG-ImageHeader:Compression=Deflate/Inflate
-PNG-ImageHeader:Filter=Adaptive
-PNG-ImageHeader:Interlace=Noninterlaced
-Composite:ImageSize=900x604
-Composite:Megapixels=0.544

[agriggio]

Please ack that this works also for libpng 1.6.x:

diff --git a/rtengine/imageio.cc b/rtengine/imageio.cc
--- a/rtengine/imageio.cc
+++ b/rtengine/imageio.cc
@@ -365,10 +365,10 @@
     if (png_get_valid(png, info, PNG_INFO_iCCP)) {
         png_charp name;
         int compression_type;
-#if PNG_LIBPNG_VER_MAJOR > 1 || (PNG_LIBPNG_VER_MAJOR == 1 && PNG_LIBPNG_VER_MINOR > 4)
+#if PNG_LIBPNG_VER < 10500
+        png_charp profdata;
+#else
         png_bytep profdata;
-#else
-        png_charp profdata;
 #endif
         png_uint_32 proflen;
         png_get_iCCP(png, info, &name, &compression_type, &profdata, &proflen);
@@ -950,6 +950,11 @@
         return IMIO_HEADERERROR;
     }
 
+    // silence the warning about "invalid" sRGB profiles -- see #4260
+#if defined(PNG_SKIP_sRGB_CHECK_PROFILE) && defined(PNG_SET_OPTION_SUPPORTED)
+    png_set_option(png, PNG_SKIP_sRGB_CHECK_PROFILE, PNG_OPTION_ON);
+#endif
+    
     png_infop info = png_create_info_struct(png);
 
     if (!info) {
@@ -980,6 +985,15 @@
     png_set_IHDR(png, info, width, height, bps, PNG_COLOR_TYPE_RGB,
                  PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_BASE);
 
+    if (profileData) {
+#if PNG_LIBPNG_VER < 10500
+        png_charp profdata = static_cast<png_charp>(profileData);
+#else
+        png_bytep profdata = static_cast<png_bytep>(profileData);
+#endif
+        png_set_iCCP(png, info, const_cast<png_charp>("icc"), 0, profdata, profileLength);
+    }
+
 
     int rowlen = width * 3 * bps / 8;
     unsigned char *row = new unsigned char [rowlen];

[Beep6581]

@agriggio awesome to see a patch!
Compilation fails:

/home/morgan/programs/code-rawtherapee/rtengine/imageio.cc: In member function ‘int rtengine::ImageIO::savePNG(Glib::ustring, int)’:
/home/morgan/programs/code-rawtherapee/rtengine/imageio.cc:992:64: error: invalid static_cast from type ‘char*’ to type ‘png_bytep {aka unsigned char*}’
         png_bytep profdata = static_cast<png_bytep>(profileData);
                                                                ^

[agriggio]

@Beep6581 replace with const_cast and it should work.
incidentally, this is one reason why c-style casts aren't always a mortal sin :-)

[Beep6581]

@agriggio

/home/morgan/programs/code-rawtherapee/rtengine/imageio.cc: In member function ‘int rtengine::ImageIO::savePNG(Glib::ustring, int)’:
/home/morgan/programs/code-rawtherapee/rtengine/imageio.cc:992:63: error: invalid const_cast from type ‘char*’ to type ‘png_bytep {aka unsigned char*}’
         png_bytep profdata = const_cast<png_bytep>(profileData);
                                                               ^

[agriggio]

I should read better the error messages before replying :-)
a reinterpret_cast should do, or a c-style also, i.e. (png_bytep)profileData

(I am on my phone now so I can't test)

[Beep6581]

Compiled!

[Beep6581]

Tested, no issues found. Thank you @agriggio , +1 for commit.