don't encode alpha channel twice when alpha is different colorspace from other channels

tests/resample_test.cpp

@@ -148,25 +148,26 @@ static void performance(int argc, char **argv)
 	int w, h, count;
 	int n, i;
 	int out_w, out_h, srgb=1;
-	input_pixels = stbi_load(argv[1], &w, &h, &n, 0);
-    #if 1
+	input_pixels = stbi_load(argv[1], &w, &h, &n, 4);
+    n=4;
+    #if 0
     out_w = w/4; out_h = h/4; count=100; // 1
     #elif 0
 	out_w = w*2; out_h = h/4; count=20; // 2   // note this is structured pessimily, would be much faster to downsample vertically first
     #elif 0
     out_w = w/4; out_h = h*2; count=50; // 3
     #elif 0
-    out_w = w*3; out_h = h*3; count=5; srgb=0; // 4
+    out_w = w*3; out_h = h*3; count=2; srgb=0; // 4
     #else
-    out_w = w*3; out_h = h*3; count=3; // 5   // this is dominated by linear->sRGB conversion
+    out_w = w*3; out_h = h*3; count=1; // 5   // this is dominated by linear->sRGB conversion
     #endif
 
 	output_pixels = (unsigned char*) malloc(out_w*out_h*n);
     for (i=0; i < count; ++i)
         if (srgb)
-	        stbir_resize_uint8_srgb(input_pixels, w, h, 0, output_pixels, out_w, out_h, 0, n, -1,0);
+	        stbir_resize_uint8_srgb(input_pixels, w, h, 0, output_pixels, out_w, out_h, 0, n, 3,0);
         else
-	        stbir_resize_uint8(input_pixels, w, h, 0, output_pixels, out_w, out_h, 0, n);
+	        stbir_resize(input_pixels, w, h, 0, output_pixels, out_w, out_h, 0, STBIR_TYPE_UINT8, n, 3, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_DEFAULT, STBIR_FILTER_DEFAULT, STBIR_COLORSPACE_LINEAR, NULL);
 	exit(0);
 }
 
@@ -228,6 +229,7 @@ void test_format(const char* file, float width_percent, float height_percent, st
 	int new_h = (int)(h * height_percent);
 
 	T* T_data = (T*)malloc(w * h * n * sizeof(T));
+    memset(T_data, 0, w*h*n*sizeof(T));
 	convert_image<unsigned char, T>(input_data, T_data, w * h * n);
 
 	T* output_data = (T*)malloc(new_w * new_h * n * sizeof(T));
@@ -792,13 +794,15 @@ void test_suite(int argc, char **argv)
 
 	_mkdir("test-output");
 
-    test_32();
-
 	if (argc > 1)
 		barbara = argv[1];
 	else
 		barbara = "barbara.png";
 
+	test_format<unsigned short>(barbara, 0.5, 2.0, STBIR_TYPE_UINT16, STBIR_COLORSPACE_SRGB);
+    test_32();
+
+
 	// check what cases we need normalization for
 #if 1
 	{