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Normalize downsample coefficients.

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This commit is contained in:
Jorge Rodriguez 2014-09-09 15:22:29 -07:00
parent 43fbc1d5e3
commit 497eab8339
2 changed files with 31 additions and 9 deletions
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20
stb_image_resize.h
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@ -793,8 +793,7 @@ static void stbir__calculate_coefficients_downsample(stbir__info* stbir_info, st
}
}
#ifdef STBIR_DEBUG
static void stbir__check_downsample_coefficients(stbir__info* stbir_info)
static void stbir__normalize_downsample_coefficients(stbir__info* stbir_info)
{
int i;
for (i = 0; i < stbir_info->output_w; i++)
@ -813,10 +812,19 @@ static void stbir__check_downsample_coefficients(stbir__info* stbir_info)
}
STBIR__DEBUG_ASSERT(total > 0.9f);
STBIR__DEBUG_ASSERT(total <= 1.0f + 1.0f / (pow(2.0f, 8.0f * stbir__type_size[stbir_info->type]) - 1));
STBIR__DEBUG_ASSERT(total < 1.1f);
float scale = 1 / total;
for (j = 0; j < stbir__get_horizontal_contributors(stbir_info); j++)
{
if (i >= stbir_info->horizontal_contributors[j].n0 && i <= stbir_info->horizontal_contributors[j].n1)
*stbir__get_coefficient(stbir_info, j, i - stbir_info->horizontal_contributors[j].n0) *= scale;
else if (i < stbir_info->horizontal_contributors[j].n0)
break;
}
}
}
#endif
// Each scan line uses the same kernel values so we should calculate the kernel
// values once and then we can use them for every scan line.
@ -858,9 +866,7 @@ static void stbir__calculate_horizontal_filters(stbir__info* stbir_info)
stbir__calculate_coefficients_downsample(stbir_info, stbir_info->horizontal_filter, scale_ratio, out_first_pixel, out_last_pixel, out_center_of_in, stbir__get_contributor(stbir_info, n), stbir__get_coefficient(stbir_info, n, 0));
}
#ifdef STBIR_DEBUG
stbir__check_downsample_coefficients(stbir_info);
#endif
stbir__normalize_downsample_coefficients(stbir_info);
}
}

20
tests/resample_test.cpp
View File

@ -631,6 +631,22 @@ void test_filters(void)
verify_filter_normalized(STBIR_FILTER_BICUBIC, 1, value);
verify_filter_normalized(STBIR_FILTER_CATMULLROM, 1, value);
verify_filter_normalized(STBIR_FILTER_MITCHELL, 1, value);
{
// This test is designed to produce coefficients that are very badly denormalized.
int v = 556;
unsigned int input[100 * 100];
unsigned int output[11 * 11];
for (j = 0; j < 100 * 100; ++j)
input[j] = v;
stbir_resize(input, 100, 100, 0, output, 11, 11, 0, STBIR_TYPE_UINT32, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BILINEAR, STBIR_FILTER_BILINEAR, STBIR_COLORSPACE_LINEAR, NULL);
for (j = 0; j < 11 * 11; ++j)
STBIR_ASSERT(v == output[j]);
}
}
@ -663,8 +679,8 @@ void test_suite(int argc, char **argv)
}
#if 1
for (y = 0.11f; y < 1; y += 0.01f) {
for (x = -1; x < 1; x += 0.05f) {
for (y = 0.11f; y < 1; y += 0.01f) { // Step
for (x = -1; x < 1; x += 0.05f) { // Phase
float sums[4] = {0};
float o;
for (o=-5; o <= 5; o += y) {