Same deal with height.

stb_resample.h

@@ -1147,7 +1147,7 @@ static void stbr__buffer_loop_downsample(stbr__info* stbr_info)
 {
 	int y;
 	float scale_ratio = (float)stbr_info->output_h / stbr_info->input_h;
-	float in_pixels_radius = stbr__filter_info_table[stbr_info->filter].support;
+	float in_pixels_radius = stbr__filter_info_table[stbr_info->filter].support / scale_ratio;
 	int max_y = stbr_info->input_h + stbr__get_filter_texel_margin(stbr_info->filter, stbr_info->input_h, stbr_info->output_h);
 
 	STBR_DEBUG_ASSERT(!stbr__use_height_upsampling(stbr_info));

tests/resample_test.cpp

@@ -137,12 +137,26 @@ void test_suite()
 		resize_image("barbara.png", (float)i / 100, 1, STBR_FILTER_CATMULLROM, STBR_EDGE_CLAMP, outname);
 	}
 
-	for (int i = 110; i < 1000; i += 10)
+	for (int i = 110; i < 500; i += 10)
 	{
 		char outname[200];
 		sprintf(outname, "test-output/barbara-width-%d.jpg", i);
 		resize_image("barbara.png", (float)i / 100, 1, STBR_FILTER_CATMULLROM, STBR_EDGE_CLAMP, outname);
 	}
+
+	for (int i = 10; i < 100; i++)
+	{
+		char outname[200];
+		sprintf(outname, "test-output/barbara-height-%d.jpg", i);
+		resize_image("barbara.png", 1, (float)i / 100, STBR_FILTER_CATMULLROM, STBR_EDGE_CLAMP, outname);
+	}
+
+	for (int i = 110; i < 500; i += 10)
+	{
+		char outname[200];
+		sprintf(outname, "test-output/barbara-height-%d.jpg", i);
+		resize_image("barbara.png", 1, (float)i / 100, STBR_FILTER_CATMULLROM, STBR_EDGE_CLAMP, outname);
+	}
 }