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Use a carefully shaped trapezoid instead of a box filter to avoid jumps between pixel values.

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This commit is contained in:
Jorge Rodriguez
2014-09-10 19:08:11 -07:00
parent 6922628106
commit 953a637841
2 changed files with 170 additions and 55 deletions
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116
tests/resample_test.cpp
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@ -48,8 +48,10 @@ void stbir_free(void* memory, void* context)
return free(memory);
}
//#include <stdio.h>
void stbir_progress(float p)
{
//printf("%f\n", p);
STBIR_ASSERT(p >= 0 && p <= 1);
}
@ -373,7 +375,7 @@ void test_subpixel(const char* file, float width_percent, float 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_CATMULLROM, STBIR_FILTER_CATMULLROM, STBIR_COLORSPACE_SRGB, &g_context, 0, 0, s1, t1);
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, 0, 0, s1, t1);
stbi_image_free(input_data);
@ -684,6 +686,72 @@ void test_filters(void)
for (j = 0; j < 11 * 11; ++j)
STBIR_ASSERT(v == output[j]);
}
{
// Now test the trapezoid filter for downsampling.
unsigned int input[3 * 1];
unsigned int output[2 * 1];
input[0] = 0;
input[1] = 255;
input[2] = 127;
stbir_resize(input, 3, 1, 0, output, 2, 1, 0, STBIR_TYPE_UINT32, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BOX, STBIR_FILTER_BOX, STBIR_COLORSPACE_LINEAR, NULL);
STBIR_ASSERT(output[0] == (int)round((float)(input[0] * 2 + input[1]) / 3));
STBIR_ASSERT(output[1] == (int)round((float)(input[2] * 2 + input[1]) / 3));
stbir_resize(input, 1, 3, 0, output, 1, 2, 0, STBIR_TYPE_UINT32, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BOX, STBIR_FILTER_BOX, STBIR_COLORSPACE_LINEAR, NULL);
STBIR_ASSERT(output[0] == (int)round((float)(input[0] * 2 + input[1]) / 3));
STBIR_ASSERT(output[1] == (int)round((float)(input[2] * 2 + input[1]) / 3));
}
{
// Now test the trapezoid filter for upsampling.
unsigned int input[2 * 1];
unsigned int output[3 * 1];
input[0] = 0;
input[1] = 255;
stbir_resize(input, 2, 1, 0, output, 3, 1, 0, STBIR_TYPE_UINT32, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BOX, STBIR_FILTER_BOX, STBIR_COLORSPACE_LINEAR, NULL);
STBIR_ASSERT(output[0] == input[0]);
STBIR_ASSERT(output[1] == (input[0] + input[1]) / 2);
STBIR_ASSERT(output[2] == input[1]);
stbir_resize(input, 1, 2, 0, output, 1, 3, 0, STBIR_TYPE_UINT32, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BOX, STBIR_FILTER_BOX, STBIR_COLORSPACE_LINEAR, NULL);
STBIR_ASSERT(output[0] == input[0]);
STBIR_ASSERT(output[1] == (input[0] + input[1]) / 2);
STBIR_ASSERT(output[2] == input[1]);
}
{
// Now for some fun.
unsigned char input[2 * 1];
unsigned char output[127 * 1];
input[0] = 0;
input[1] = 255;
stbir_resize(input, 2, 1, 0, output, 127, 1, 0, STBIR_TYPE_UINT8, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BOX, STBIR_FILTER_BOX, STBIR_COLORSPACE_LINEAR, NULL);
STBIR_ASSERT(output[0] == 0);
STBIR_ASSERT(output[127 / 2 - 1] == 0);
STBIR_ASSERT(output[127 / 2] == 128);
STBIR_ASSERT(output[127 / 2 + 1] == 255);
STBIR_ASSERT(output[126] == 255);
stbi_write_png("test-output/trapezoid-upsample-horizontal.png", 127, 1, 1, output, 0);
stbir_resize(input, 1, 2, 0, output, 1, 127, 0, STBIR_TYPE_UINT8, 1, STBIR_ALPHA_CHANNEL_NONE, 0, STBIR_EDGE_CLAMP, STBIR_EDGE_CLAMP, STBIR_FILTER_BOX, STBIR_FILTER_BOX, STBIR_COLORSPACE_LINEAR, NULL);
STBIR_ASSERT(output[0] == 0);
STBIR_ASSERT(output[127 / 2 - 1] == 0);
STBIR_ASSERT(output[127 / 2] == 128);
STBIR_ASSERT(output[127 / 2 + 1] == 255);
STBIR_ASSERT(output[126] == 255);
stbi_write_png("test-output/trapezoid-upsample-vertical.png", 1, 127, 1, output, 0);
}
}
@ -699,52 +767,54 @@ void test_suite(int argc, char **argv)
else
barbara = "barbara.png";
#if 1
#if 1
{
float x,y;
float x, y;
for (x = -1; x < 1; x += 0.05f) {
float sums[4] = {0};
float sums[5] = { 0 };
float o;
for (o=-5; o <= 5; ++o) {
sums[0] += stbir__filter_mitchell(x+o);
sums[1] += stbir__filter_catmullrom(x+o);
sums[2] += stbir__filter_bicubic(x+o);
sums[3] += stbir__filter_bilinear(x+o);
for (o = -5; o <= 5; ++o) {
sums[0] += stbir__filter_mitchell(x + o, 1);
sums[1] += stbir__filter_catmullrom(x + o, 1);
sums[2] += stbir__filter_bicubic(x + o, 1);
sums[3] += stbir__filter_bilinear(x + o, 1);
sums[4] += stbir__filter_trapezoid(x + o, 0.5f);
}
for (i=0; i < 4; ++i)
for (i = 0; i < 5; ++i)
STBIR_ASSERT(sums[i] >= 1.0 - 0.001 && sums[i] <= 1.0 + 0.001);
}
#if 1
#if 1
for (y = 0.11f; y < 1; y += 0.01f) { // Step
for (x = -1; x < 1; x += 0.05f) { // Phase
float sums[4] = {0};
float sums[5] = { 0 };
float o;
for (o=-5; o <= 5; o += y) {
sums[0] += y * stbir__filter_mitchell(x+o);
sums[1] += y * stbir__filter_catmullrom(x+o);
sums[2] += y * stbir__filter_bicubic(x+o);
sums[3] += y * stbir__filter_bilinear(x+o);
for (o = -5; o <= 5; o += y) {
sums[0] += y * stbir__filter_mitchell(x + o, 1);
sums[1] += y * stbir__filter_catmullrom(x + o, 1);
sums[2] += y * stbir__filter_bicubic(x + o, 1);
sums[4] += y * stbir__filter_trapezoid(x + o, 0.5f);
sums[3] += y * stbir__filter_bilinear(x + o, 1);
}
for (i=0; i < 3; ++i)
for (i = 0; i < 3; ++i)
STBIR_ASSERT(sums[i] >= 1.0 - 0.0170 && sums[i] <= 1.0 + 0.0170);
}
}
#endif
#endif
}
#endif
#endif
for (i = 0; i < 256; i++)
STBIR_ASSERT(stbir__linear_to_srgb_uchar(stbir__srgb_to_linear(float(i)/255)) == i);
STBIR_ASSERT(stbir__linear_to_srgb_uchar(stbir__srgb_to_linear(float(i) / 255)) == i);
#if 0 // linear_to_srgb_uchar table
#if 0 // linear_to_srgb_uchar table
for (i=0; i < 256; ++i) {
float f = stbir__srgb_to_linear((i+0.5f)/256.0f);
printf("%9d, ", (int) ((f) * (1<<28)));
if ((i & 7) == 7)
printf("\n");
}
#endif
#endif
test_filters();