+ DCPOMATIC_ASSERT (bytes_per_pixel(0) == 4);
+ DCPOMATIC_ASSERT (planes() == 1);
+ if (pixel_format() != AV_PIX_FMT_RGBA) {
+ return convert_pixel_format(dcp::YUV_TO_RGB_REC709, AV_PIX_FMT_RGBA, true, false)->as_png();
+ }
+
+ /* error handling? */
+ png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, reinterpret_cast<void*>(const_cast<Image*>(this)), png_error_fn, 0);
+ if (!png_ptr) {
+ throw EncodeError (N_("could not create PNG write struct"));
+ }
+
+ Memory state;
+
+ png_set_write_fn (png_ptr, &state, png_write_data, png_flush);
+
+ png_infop info_ptr = png_create_info_struct(png_ptr);
+ if (!info_ptr) {
+ png_destroy_write_struct (&png_ptr, &info_ptr);
+ throw EncodeError (N_("could not create PNG info struct"));
+ }
+
+ png_set_IHDR (png_ptr, info_ptr, size().width, size().height, 8, PNG_COLOR_TYPE_RGBA, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+
+ png_byte ** row_pointers = reinterpret_cast<png_byte **>(png_malloc(png_ptr, size().height * sizeof(png_byte *)));
+ for (int i = 0; i < size().height; ++i) {
+ row_pointers[i] = (png_byte *) (data()[0] + i * stride()[0]);
+ }
+
+ png_write_info (png_ptr, info_ptr);
+ png_write_image (png_ptr, row_pointers);
+ png_write_end (png_ptr, info_ptr);
+
+ png_destroy_write_struct (&png_ptr, &info_ptr);
+ png_free (png_ptr, row_pointers);
+
+ return dcp::ArrayData (state.data, state.size);
+}
+