From cf6f69cdc9ea4d0cc7f1fb86e724a31b1e61926b Mon Sep 17 00:00:00 2001 From: Jorge Rodriguez Date: Sun, 8 Nov 2015 16:40:32 -0800 Subject: [PATCH] Fix the calculation of the input image shift when using subpixel regions. Includes some more tests which had incorrect results before and now work fine. --- stb_image_resize.h | 20 ++++++++++---------- tests/resample_test.cpp | 40 +++++++++++++++++++++++++++++++++++++++- 2 files changed, 49 insertions(+), 11 deletions(-) diff --git a/stb_image_resize.h b/stb_image_resize.h index 4ce7ddb..fde37d8 100644 --- a/stb_image_resize.h +++ b/stb_image_resize.h @@ -1004,31 +1004,31 @@ stbir__inline static int stbir__edge_wrap(stbir_edge edge, int n, int max) } // What input pixels contribute to this output pixel? -static void stbir__calculate_sample_range_upsample(int n, float out_filter_radius, float scale_ratio, float out_shift, int* in_first_pixel, int* in_last_pixel, float* in_center_of_out) +static void stbir__calculate_sample_range_upsample(int n, float out_filter_radius, float scale_ratio, float in_shift, int* in_first_pixel, int* in_last_pixel, float* in_center_of_out) { float out_pixel_center = (float)n + 0.5f; float out_pixel_influence_lowerbound = out_pixel_center - out_filter_radius; float out_pixel_influence_upperbound = out_pixel_center + out_filter_radius; - float in_pixel_influence_lowerbound = (out_pixel_influence_lowerbound + out_shift) / scale_ratio; - float in_pixel_influence_upperbound = (out_pixel_influence_upperbound + out_shift) / scale_ratio; + float in_pixel_influence_lowerbound = out_pixel_influence_lowerbound / scale_ratio + in_shift; + float in_pixel_influence_upperbound = out_pixel_influence_upperbound / scale_ratio + in_shift; - *in_center_of_out = (out_pixel_center + out_shift) / scale_ratio; + *in_center_of_out = out_pixel_center / scale_ratio + in_shift; *in_first_pixel = (int)(floor(in_pixel_influence_lowerbound + 0.5)); *in_last_pixel = (int)(floor(in_pixel_influence_upperbound - 0.5)); } // What output pixels does this input pixel contribute to? -static void stbir__calculate_sample_range_downsample(int n, float in_pixels_radius, float scale_ratio, float out_shift, int* out_first_pixel, int* out_last_pixel, float* out_center_of_in) +static void stbir__calculate_sample_range_downsample(int n, float in_pixels_radius, float scale_ratio, float in_shift, int* out_first_pixel, int* out_last_pixel, float* out_center_of_in) { float in_pixel_center = (float)n + 0.5f; float in_pixel_influence_lowerbound = in_pixel_center - in_pixels_radius; float in_pixel_influence_upperbound = in_pixel_center + in_pixels_radius; - float out_pixel_influence_lowerbound = in_pixel_influence_lowerbound * scale_ratio - out_shift; - float out_pixel_influence_upperbound = in_pixel_influence_upperbound * scale_ratio - out_shift; + float out_pixel_influence_lowerbound = (in_pixel_influence_lowerbound - in_shift) * scale_ratio; + float out_pixel_influence_upperbound = (in_pixel_influence_upperbound - in_shift) * scale_ratio; - *out_center_of_in = in_pixel_center * scale_ratio - out_shift; + *out_center_of_in = (in_pixel_center - in_shift) * scale_ratio; *out_first_pixel = (int)(floor(out_pixel_influence_lowerbound + 0.5)); *out_last_pixel = (int)(floor(out_pixel_influence_upperbound - 0.5)); } @@ -2229,8 +2229,8 @@ static void stbir__calculate_transform(stbir__info *info, float s0, float t0, fl info->horizontal_scale = ((float)info->output_w / info->input_w) / (s1 - s0); info->vertical_scale = ((float)info->output_h / info->input_h) / (t1 - t0); - info->horizontal_shift = s0 * info->input_w / (s1 - s0); - info->vertical_shift = t0 * info->input_h / (t1 - t0); + info->horizontal_shift = s0 * info->input_w; + info->vertical_shift = t0 * info->input_h; } } diff --git a/tests/resample_test.cpp b/tests/resample_test.cpp index c42df7b..3bd3402 100644 --- a/tests/resample_test.cpp +++ b/tests/resample_test.cpp @@ -1,4 +1,5 @@ -#include +#include +#include #if defined(_WIN32) && _MSC_VER > 1200 #define STBIR_ASSERT(x) \ @@ -356,6 +357,30 @@ void test_subpixel(const char* file, float width_percent, float height_percent, free(output_data); } +void test_subpixel_really(const char* file, float width_percent, float height_percent, float s0, float t0, float s1, float t1) +{ + int w, h, n; + unsigned char* input_data = stbi_load(file, &w, &h, &n, 0); + + if (input_data == NULL) + return; + + int new_w = (int)(w * width_percent); + int new_h = (int)(h * height_percent); + + unsigned char* output_data = (unsigned char*)malloc(new_w * new_h * n * sizeof(unsigned char)); + + stbir_resize_region(input_data, w, h, 0, output_data, new_w, new_h, 0, STBIR_TYPE_UINT8, n, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BOX, STBIR_FILTER_CATMULLROM, STBIR_COLORSPACE_SRGB, &g_context, s0, t0, s1, t1); + + stbi_image_free(input_data); + + char output[200]; + sprintf(output, "test-output/subpixel-really-%d-%d-%f-%f-%f-%f-%s", new_w, new_h, s0, t0, s1, t1, file); + stbi_write_png(output, new_w, new_h, n, output_data, 0); + + free(output_data); +} + unsigned int* pixel(unsigned int* buffer, int x, int y, int c, int w, int n) { return &buffer[y*w*n + x*n + c]; @@ -880,6 +905,19 @@ void test_suite(int argc, char **argv) stbir_resize(image88, 8, 8, 0, output88, 16, 4, 0, STBIR_TYPE_UINT8, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BOX, STBIR_FILTER_CATMULLROM, STBIR_COLORSPACE_SRGB, &g_context); stbir_resize(image88, 8, 8, 0, output88, 16, 4, 0, STBIR_TYPE_UINT8, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_CATMULLROM, STBIR_FILTER_BOX, STBIR_COLORSPACE_SRGB, &g_context); + int res = 10; + for (int i = 0; i < res; i++) + { + float t = (float)i/res / 2; + test_subpixel_really(barbara, 0.5f, 0.5f, t, t, t+0.5f, t+0.5f); + } + + for (int i = 0; i < res; i++) + { + float t = (float)i/res / 2; + test_subpixel_really(barbara, 2, 2, t, t, t+0.5f, t+0.5f); + } + for (i = 0; i < 10; i++) test_subpixel(barbara, 0.5f, 0.5f, (float)i / 10, 1);