diff --git a/common/waifu2x.cpp b/common/waifu2x.cpp
index 1943f3b..fa76d4f 100644
--- a/common/waifu2x.cpp
+++ b/common/waifu2x.cpp
@@ -71,13 +71,35 @@ bool can_use_cuDNN()
 // 画像を読み込んで値を0.0f〜1.0fの範囲に変換
 eWaifu2xError LoadImage(cv::Mat &float_image, const std::string &input_file)
 {
-	cv::Mat original_image = cv::imread(input_file, cv::IMREAD_COLOR);
+	cv::Mat original_image = cv::imread(input_file, cv::IMREAD_UNCHANGED);
 	if (original_image.empty())
 		return eWaifu2xError_FailedOpenInputFile;
 
-	original_image.convertTo(float_image, CV_32F, 1.0 / 255.0);
+	cv::Mat convert;
+	original_image.convertTo(convert, CV_32F, 1.0 / 255.0);
 	original_image.release();
 
+	if (convert.channels() == 1)
+		cv::cvtColor(convert, convert, cv::COLOR_GRAY2BGR);
+	else if (convert.channels() == 4)
+	{
+		// アルファチャンネル付きだったら背景を1(白)として画像合成する
+
+		std::vector<cv::Mat> planes;
+		cv::split(convert, planes);
+
+		cv::Mat w2 = planes[3];
+		cv::Mat w1 = 1.0 - planes[3];
+
+		planes[0] = planes[0].mul(w2) + w1;
+		planes[1] = planes[1].mul(w2) + w1;
+		planes[2] = planes[2].mul(w2) + w1;
+
+		cv::merge(planes, convert);
+	}
+
+	float_image = convert;
+
 	return eWaifu2xError_OK;
 }
 
@@ -546,6 +568,17 @@ eWaifu2xError waifu2x(int argc, char** argv, const std::vector<InputOutputPathPa
 
 		std::vector<cv::Mat> color_planes;
 		CreateZoomColorImage(float_image, image_size, color_planes);
+
+		cv::Mat alpha;
+		if (float_image.channels() == 4)
+		{
+			std::vector<cv::Mat> planes;
+			cv::split(float_image, planes);
+			alpha = planes[3];
+
+			cv::resize(alpha, alpha, image_size, 0.0, 0.0, cv::INTER_CUBIC);
+		}
+
 		float_image.release();
 
 		color_planes[0] = im;
@@ -559,6 +592,24 @@ eWaifu2xError waifu2x(int argc, char** argv, const std::vector<InputOutputPathPa
 		cv::cvtColor(converted_image, process_image, ConvertInverseMode);
 		converted_image.release();
 
+		// アルファチャンネルがあったら、アルファを付加してカラーからアルファの影響を抜く
+		if (!alpha.empty())
+		{
+			std::vector<cv::Mat> planes;
+			cv::split(process_image, planes);
+			process_image.release();
+
+			planes.push_back(alpha);
+
+			cv::Mat w2 = planes[3];
+
+			planes[0] = (planes[0] - 1.0).mul(1.0 / w2) + 1.0;
+			planes[1] = (planes[1] - 1.0).mul(1.0 / w2) + 1.0;
+			planes[2] = (planes[2] - 1.0).mul(1.0 / w2) + 1.0;
+
+			cv::merge(planes, process_image);
+		}
+
 		const cv::Size_<int> ns(image_size.width * shrinkRatio, image_size.height * shrinkRatio);
 		if (image_size.width != ns.width || image_size.height != ns.height)
 			cv::resize(process_image, process_image, ns, 0.0, 0.0, cv::INTER_LINEAR);