Mercurial > octave-dspies

comparison libinterp/dldfcn/__magick_read__.cc @ 18957:87cba451fd5e stable

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
__magick_read__.cc: fix png check for image class in older GM (bug #42834).
author Carnë Draug <carandraug@octave.org>
date Thu, 24 Jul 2014 17:37:45 +0100
parents 548643c76a88
children
comparison
equal deleted inserted replaced
18956:ab5983dc0587 18957:87cba451fd5e
72 // 2) A PNG file is only an indexed image if color type orig is 3 (value comes 72 // 2) A PNG file is only an indexed image if color type orig is 3 (value comes
73 // from libpng) 73 // from libpng)
74 static bool 74 static bool
75 is_indexed (const Magick::Image& img) 75 is_indexed (const Magick::Image& img)
76 { 76 {
77 bool retval = false; 77 bool indexed = (img.classType () == Magick::PseudoClass);
78 const std::string format = img.magick (); 78 // Our problem until now is non-indexed images, being represented as indexed
79 if (img.classType () == Magick::PseudoClass 79 // by GM. The following attempts educated guesses to undo this optimization.
80 && format != "JPEG" 80 if (indexed)
81 && (format != "PNG" 81 {
82 || const_cast<Magick::Image&> (img).attribute ("PNG:IHDR.color-type-orig") == "3")) 82 const std::string fmt = img.magick ();
83 retval = true; 83 if (fmt == "JPEG")
84 84 // The JPEG format does not support indexed images, but GM sometimes
85 return retval; 85 // reports grayscale JPEG as indexed. Always false for JPEG.
86 indexed = false;
87 else if (fmt == "PNG")
88 {
89 // Newer versions of GM (at least does not happens with 1.3.16) will
90 // store values from the underlying library as image attributes. In
91 // the case of PNG files, this is libpng where an indexed image will
92 // always have a value of 3 for "color-type-orig". This property
93 // always has a value in libpng so if we get nothing, we assume this
94 // GM version does not store them and we have to go with whatever
95 // GM PseudoClass says.
96 const std::string color_type =
97 const_cast<Magick::Image&> (img).attribute ("PNG:IHDR.color-type-orig");
98 if (! color_type.empty() && color_type != "3")
99 indexed = false;
100 }
101 }
102 return indexed;
86 } 103 }
87 104
88 // The depth from depth() is not always correct for us but seems to be the 105 // The depth from depth() is not always correct for us but seems to be the
89 // best value we can get. For example, a grayscale png image with 1 bit 106 // best value we can get. For example, a grayscale png image with 1 bit
90 // per channel should return a depth of 1 but instead we get 8. 107 // per channel should return a depth of 1 but instead we get 8.