Added support for RGBA in png

bob/io/image/png.cpp

@@ -97,10 +97,10 @@ static void im_peek(const std::string& path, bob::io::base::array::typeinfo& inf
   info.dtype = (bit_depth <= 8 ? bob::io::base::array::t_uint8 : bob::io::base::array::t_uint16);
   if(color_type == PNG_COLOR_TYPE_GRAY)
     info.nd = 2;
-  else if (color_type == PNG_COLOR_TYPE_RGB || PNG_COLOR_TYPE_PALETTE)
+  else if (color_type == PNG_COLOR_TYPE_RGB || PNG_COLOR_TYPE_RGB_ALPHA || PNG_COLOR_TYPE_PALETTE)
     info.nd = 3;
   else {// Unsupported color type
-    throw std::runtime_error("PNG: codec does not support images with color spaces different than GRAY, RGB or Indexed colors (Palette)");
+    throw std::runtime_error("PNG: codec does not support images with color spaces different than GRAY, RGB, RGBA or Indexed colors (Palette)");
   }
   if(info.nd == 2)
   {
@@ -145,18 +145,18 @@ void im_load_gray(png_structp png_ptr, bob::io::base::array::interface& b)
 }
 
 template <typename T> static
-void imbuffer_to_rgb(const size_t size, const T* im, T* r, T* g, T* b)
+void imbuffer_to_rgb(const size_t size, const T* im, T* r, T* g, T* b, const size_t number_of_elements)
 {
   for(size_t k=0; k<size; ++k)
   {
-    r[k] = im[3*k];
-    g[k] = im[3*k +1];
-    b[k] = im[3*k +2];
+    r[k] = im[number_of_elements*k];
+    g[k] = im[number_of_elements*k +1];
+    b[k] = im[number_of_elements*k +2];
   }
 }
 
 template <typename T> static
-void im_load_color(png_structp png_ptr, bob::io::base::array::interface& b)
+void im_load_color(png_structp png_ptr, bob::io::base::array::interface& b, bool has_alpha)
 {
   const bob::io::base::array::typeinfo& info = b.type();
   const size_t height = info.shape[1];
@@ -164,8 +164,10 @@ void im_load_color(png_structp png_ptr, bob::io::base::array::interface& b)
   const size_t frame_size = height * width;
   const size_t row_color_stride = width;
 
+  const size_t number_of_elements = has_alpha ? 4 : 3;
+
   // Allocate array to contains a row of RGB-like pixels
-  boost::shared_array<T> row(new T[3*width]);
+  boost::shared_array<T> row(new T[number_of_elements*width]);
   png_bytep row_pointer = reinterpret_cast<png_bytep>(row.get());
 
 #ifdef PNG_READ_INTERLACING_SUPPORTED
@@ -189,7 +191,7 @@ void im_load_color(png_structp png_ptr, bob::io::base::array::interface& b)
     for(size_t y=0; y<height; ++y)
     {
       png_read_row(png_ptr, row_pointer, NULL);
-      imbuffer_to_rgb(row_color_stride, reinterpret_cast<T*>(row_pointer), element_r, element_g, element_b);
+      imbuffer_to_rgb(row_color_stride, reinterpret_cast<T*>(row_pointer), element_r, element_g, element_b, number_of_elements);
       element_r += row_color_stride;
       element_g += row_color_stride;
       element_b += row_color_stride;
@@ -251,15 +253,19 @@ static void im_load(const std::string& filename, bob::io::base::array::interface
   else if(color_type == PNG_COLOR_TYPE_PALETTE)
     png_set_palette_to_rgb(png_ptr);
   // We currently only support grayscale and rgb images
-  if(color_type != PNG_COLOR_TYPE_GRAY && color_type != PNG_COLOR_TYPE_RGB && color_type != PNG_COLOR_TYPE_PALETTE) {
-    throw std::runtime_error("PNG: codec does not support images with color spaces different than GRAY, RGB or Indexed colors (Palette)");
+  if(color_type != PNG_COLOR_TYPE_GRAY &&
+     color_type != PNG_COLOR_TYPE_RGB &&
+     color_type != PNG_COLOR_TYPE_PALETTE &&
+     color_type != PNG_COLOR_TYPE_RGB_ALPHA) {
+    throw std::runtime_error("PNG: codec does not support images with color spaces different than GRAY, RGB, RGBA or Indexed colors (Palette)");
   }
 
   // 7. Read content
   const bob::io::base::array::typeinfo& info = b.type();
+  bool has_alpha = (color_type & PNG_COLOR_MASK_ALPHA) == PNG_COLOR_MASK_ALPHA;
   if(info.dtype == bob::io::base::array::t_uint8) {
     if(info.nd == 2) im_load_gray<uint8_t>(png_ptr, b);
-    else if( info.nd == 3) im_load_color<uint8_t>(png_ptr, b);
+    else if( info.nd == 3) im_load_color<uint8_t>(png_ptr, b, has_alpha);
     else {
       png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
       boost::format m("the image in file `%s' has a number of dimensions for which this png codec has no support for: %s");
@@ -269,7 +275,7 @@ static void im_load(const std::string& filename, bob::io::base::array::interface
   }
   else if(info.dtype == bob::io::base::array::t_uint16) {
     if(info.nd == 2) im_load_gray<uint16_t>(png_ptr, b);
-    else if( info.nd == 3) im_load_color<uint16_t>(png_ptr, b);
+    else if( info.nd == 3) im_load_color<uint16_t>(png_ptr, b, has_alpha);
     else {
       png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
       boost::format m("the image in file `%s' has a number of dimensions for which this png codec has no support for: %s");

bob/io/image/test.py

@@ -14,6 +14,7 @@ from bob.io.base import load, write, test_utils
 
 # These are some global parameters for the test.
 PNG_INDEXED_COLOR = test_utils.datafile('img_indexed_color.png', __name__)
+PNG_RGBA_COLOR = test_utils.datafile('img_rgba_color.png', __name__)
 
 def test_png_indexed_color():
 
@@ -23,6 +24,15 @@ def test_png_indexed_color():
   assert img[0,0,0] == 255
   assert img[0,17,17] == 117
 
+def test_png_rgba_color():
+
+  # Read an indexed color PNG image, and compared with hardcoded values
+  img = load(PNG_RGBA_COLOR)
+  assert img.shape == (3,22,32)
+  assert img[0,0,0] == 255
+  assert img[0,17,17] == 117
+
+
 def transcode(filename):
 
   tmpname = test_utils.temporary_filename(suffix=os.path.splitext(filename)[1])