diff --git a/src/mat_pixel.cpp b/src/mat_pixel.cpp
index 3978afc0e..a6d9d6b83 100644
--- a/src/mat_pixel.cpp
+++ b/src/mat_pixel.cpp
@@ -2269,6 +2269,7 @@ Mat Mat::from_pixels(const unsigned char* pixels, int type, int w, int h, Alloca
     }
 
     // unknown convert type
+    NCNN_LOGE("unknown convert type %d", type);
     return Mat();
 }
 
@@ -2326,6 +2327,7 @@ Mat Mat::from_pixels(const unsigned char* pixels, int type, int w, int h, int st
             break;
         default:
             // unimplemented convert type
+            NCNN_LOGE("unimplemented convert type %d", type);
             break;
         }
     }
@@ -2362,6 +2364,7 @@ Mat Mat::from_pixels_resize(const unsigned char* pixels, int type, int w, int h,
     }
 
     // unknown convert type
+    NCNN_LOGE("unknown convert type %d", type);
     return Mat();
 }
 
@@ -2395,6 +2398,7 @@ Mat Mat::from_pixels_resize(const unsigned char* pixels, int type, int w, int h,
     }
 
     // unknown convert type
+    NCNN_LOGE("unknown convert type %d", type);
     return Mat();
 }
 
@@ -2444,6 +2448,7 @@ void Mat::to_pixels(unsigned char* pixels, int type, int stride) const
             break;
         default:
             // unimplemented convert type
+            NCNN_LOGE("unimplemented convert type %d", type);
             break;
         }
     }
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index ba6577ec3..57b202b96 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -21,6 +21,7 @@ include_directories(${CMAKE_CURRENT_SOURCE_DIR}/../src)
 include_directories(${CMAKE_CURRENT_SOURCE_DIR}/../src/layer)
 
 ncnn_add_test(mat_pixel_rotate)
+ncnn_add_test(mat_pixel)
 ncnn_add_test(squeezenet)
 
 ncnn_add_layer_test(AbsVal)
diff --git a/tests/test_mat_pixel.cpp b/tests/test_mat_pixel.cpp
new file mode 100644
index 000000000..a5860c285
--- /dev/null
+++ b/tests/test_mat_pixel.cpp
@@ -0,0 +1,204 @@
+// Tencent is pleased to support the open source community by making ncnn available.
+//
+// Copyright (C) 2020 THL A29 Limited, a Tencent company. All rights reserved.
+//
+// Licensed under the BSD 3-Clause License (the "License"); you may not use this file except
+// in compliance with the License. You may obtain a copy of the License at
+//
+// https://opensource.org/licenses/BSD-3-Clause
+//
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+#include "mat.h"
+#include "prng.h"
+
+#include <string.h>
+
+static struct prng_rand_t g_prng_rand_state;
+#define SRAND(seed) prng_srand(seed, &g_prng_rand_state)
+#define RAND()      prng_rand(&g_prng_rand_state)
+
+static ncnn::Mat RandomMat(int w, int h, int elempack)
+{
+    ncnn::Mat m(w, h, (size_t)elempack, elempack);
+
+    unsigned char* p = m;
+    for (int i = 0; i < w * h * elempack; i++)
+    {
+        p[i] = RAND() % 256;
+    }
+
+    return m;
+}
+
+static int test_mat_pixel_gray(int w, int h)
+{
+    int pixel_type_from[5] = {ncnn::Mat::PIXEL_GRAY, ncnn::Mat::PIXEL_GRAY2RGB, ncnn::Mat::PIXEL_GRAY2BGR, ncnn::Mat::PIXEL_GRAY2RGBA, ncnn::Mat::PIXEL_GRAY2BGRA};
+    int pixel_type_to[5] = {ncnn::Mat::PIXEL_GRAY, ncnn::Mat::PIXEL_RGB2GRAY, ncnn::Mat::PIXEL_BGR2GRAY, ncnn::Mat::PIXEL_RGBA2GRAY, ncnn::Mat::PIXEL_BGRA2GRAY};
+
+    ncnn::Mat a = RandomMat(w, h, 1);
+
+    // FIXME enable more convert types
+    for (int i = 0; i < 1; i++)
+    {
+        ncnn::Mat m = ncnn::Mat::from_pixels(a, pixel_type_from[i], w, h);
+        ncnn::Mat b(w, h, 1u, 1);
+        m.to_pixels(b, pixel_type_to[i]);
+
+        if (memcmp(a, b, w * h * 1) != 0)
+        {
+            fprintf(stderr, "test_mat_pixel_gray failed w=%d h=%d pixel_type=%d\n", w, h, i);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int test_mat_pixel_rgb(int w, int h)
+{
+    int pixel_type_from[4] = {ncnn::Mat::PIXEL_RGB, ncnn::Mat::PIXEL_RGB2BGR, ncnn::Mat::PIXEL_RGB2RGBA, ncnn::Mat::PIXEL_RGB2BGRA};
+    int pixel_type_to[4] = {ncnn::Mat::PIXEL_RGB, ncnn::Mat::PIXEL_BGR2RGB, ncnn::Mat::PIXEL_RGBA2RGB, ncnn::Mat::PIXEL_BGRA2RGB};
+
+    ncnn::Mat a = RandomMat(w, h, 3);
+
+    // FIXME enable more convert types
+    for (int i = 0; i < 2; i++)
+    {
+        ncnn::Mat m = ncnn::Mat::from_pixels(a, pixel_type_from[i], w, h);
+        ncnn::Mat b(w, h, 3u, 3);
+        m.to_pixels(b, pixel_type_to[i]);
+
+        if (memcmp(a, b, w * h * 3) != 0)
+        {
+            fprintf(stderr, "test_mat_pixel_rgb failed w=%d h=%d pixel_type=%d\n", w, h, i);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int test_mat_pixel_bgr(int w, int h)
+{
+    int pixel_type_from[4] = {ncnn::Mat::PIXEL_BGR, ncnn::Mat::PIXEL_BGR2RGB, ncnn::Mat::PIXEL_BGR2RGBA, ncnn::Mat::PIXEL_BGR2BGRA};
+    int pixel_type_to[4] = {ncnn::Mat::PIXEL_BGR, ncnn::Mat::PIXEL_RGB2BGR, ncnn::Mat::PIXEL_RGBA2BGR, ncnn::Mat::PIXEL_BGRA2BGR};
+
+    ncnn::Mat a = RandomMat(w, h, 3);
+
+    // FIXME enable more convert types
+    for (int i = 0; i < 2; i++)
+    {
+        ncnn::Mat m = ncnn::Mat::from_pixels(a, pixel_type_from[i], w, h);
+        ncnn::Mat b(w, h, 3u, 3);
+        m.to_pixels(b, pixel_type_to[i]);
+
+        if (memcmp(a, b, w * h * 3) != 0)
+        {
+            fprintf(stderr, "test_mat_pixel_bgr failed w=%d h=%d pixel_type=%d\n", w, h, i);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int test_mat_pixel_rgba(int w, int h)
+{
+    int pixel_type_from[2] = {ncnn::Mat::PIXEL_RGBA, ncnn::Mat::PIXEL_RGBA2BGRA};
+    int pixel_type_to[2] = {ncnn::Mat::PIXEL_RGBA, ncnn::Mat::PIXEL_BGRA2RGBA};
+
+    ncnn::Mat a = RandomMat(w, h, 4);
+
+    for (int i = 0; i < 2; i++)
+    {
+        ncnn::Mat m = ncnn::Mat::from_pixels(a, pixel_type_from[i], w, h);
+        ncnn::Mat b(w, h, 4u, 4);
+        m.to_pixels(b, pixel_type_to[i]);
+
+        if (memcmp(a, b, w * h * 4) != 0)
+        {
+            fprintf(stderr, "test_mat_pixel_rgba failed w=%d h=%d pixel_type=%d\n", w, h, i);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int test_mat_pixel_bgra(int w, int h)
+{
+    int pixel_type_from[2] = {ncnn::Mat::PIXEL_BGRA, ncnn::Mat::PIXEL_BGRA2RGBA};
+    int pixel_type_to[2] = {ncnn::Mat::PIXEL_BGRA, ncnn::Mat::PIXEL_RGBA2BGRA};
+
+    ncnn::Mat a = RandomMat(w, h, 4);
+
+    for (int i = 0; i < 2; i++)
+    {
+        ncnn::Mat m = ncnn::Mat::from_pixels(a, pixel_type_from[i], w, h);
+        ncnn::Mat b(w, h, 4u, 4);
+        m.to_pixels(b, pixel_type_to[i]);
+
+        if (memcmp(a, b, w * h * 4) != 0)
+        {
+            fprintf(stderr, "test_mat_pixel_bgra failed w=%d h=%d pixel_type=%d\n", w, h, i);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int test_mat_pixel_0()
+{
+    return 0
+           || test_mat_pixel_gray(16, 16)
+           || test_mat_pixel_rgb(16, 16)
+           || test_mat_pixel_bgr(16, 16)
+           || test_mat_pixel_rgba(16, 16)
+           || test_mat_pixel_bgra(16, 16);
+}
+
+static int test_mat_pixel_1()
+{
+    return 0
+           || test_mat_pixel_gray(15, 15)
+           || test_mat_pixel_rgb(15, 15)
+           || test_mat_pixel_bgr(15, 15)
+           || test_mat_pixel_rgba(15, 15)
+           || test_mat_pixel_bgra(15, 15);
+}
+
+static int test_mat_pixel_2()
+{
+    return 0
+           || test_mat_pixel_gray(1, 1)
+           || test_mat_pixel_rgb(1, 1)
+           || test_mat_pixel_bgr(1, 1)
+           || test_mat_pixel_rgba(1, 1)
+           || test_mat_pixel_bgra(1, 1);
+}
+
+static int test_mat_pixel_3()
+{
+    return 0
+           || test_mat_pixel_gray(3, 3)
+           || test_mat_pixel_rgb(3, 3)
+           || test_mat_pixel_bgr(3, 3)
+           || test_mat_pixel_rgba(3, 3)
+           || test_mat_pixel_bgra(3, 3);
+}
+
+int main()
+{
+    SRAND(7767517);
+
+    return 0
+           || test_mat_pixel_0()
+           || test_mat_pixel_1()
+           || test_mat_pixel_2()
+           || test_mat_pixel_3();
+}