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In some situations with certain filter kernels with negative values it's possible to generate valid results > 1.0, so saturate it before we write it to make sure it doesn't overflow. Also fix incorrect filter radius while downsampling.

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This commit is contained in:
Jorge Rodriguez 2014-07-26 22:49:56 -07:00
parent af1ed58f51
commit 41dc4c476c
1 changed files with 46 additions and 15 deletions
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61
stb_resample.h
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@ -214,6 +214,17 @@ static stbr_inline int stbr__max(int a, int b)
return a > b ? a : b;
}
static stbr_inline float stbr__saturate(float x)
{
if (x < 0)
return 0;
if (x > 1)
return 1;
return x;
}
static float stbr__filter_nearest(float x)
{
@ -450,8 +461,8 @@ static void stbr__calculate_coefficients_upsample(stbr__info* stbr_info, int in_
total_filter += coefficient_group[i] = stbr__filter_info_table[filter].kernel(in_center_of_out - in_texel_center);
}
STBR_DEBUG_ASSERT(total_filter > 0);
STBR_DEBUG_ASSERT(fabs(1 - total_filter) < 0.1f); // Make sure it's not way off.
STBR_DEBUG_ASSERT(total_filter > 0.9);
STBR_DEBUG_ASSERT(total_filter < 1.1f); // Make sure it's not way off.
// Make sure the sum of all coefficients is 1.
filter_scale = 1 / total_filter;
@ -474,10 +485,34 @@ static void stbr__calculate_coefficients_downsample(stbr__info* stbr_info, float
for (i = 0; i <= out_last_texel - out_first_texel; i++)
{
float in_texel_center = (float)(i + out_first_texel) + 0.5f;
coefficient_group[i] = stbr__filter_info_table[filter].kernel(out_center_of_in - in_texel_center) * scale_ratio;
coefficient_group[i] = stbr__filter_info_table[filter].kernel((out_center_of_in - in_texel_center)/scale_ratio);
}
}
#ifdef STBR_DEBUG
static void stbr__check_downsample_coefficients(stbr__info* stbr_info)
{
for (int i = 0; i < stbr_info->output_w; i++)
{
float total = 0;
for (int j = 0; j < stbr__get_horizontal_contributors(stbr_info->filter, stbr_info->input_w, stbr_info->output_w); j++)
{
if (i >= stbr_info->horizontal_contributors[j].n0 && i <= stbr_info->horizontal_contributors[j].n1)
{
float coefficient = *stbr__get_coefficient(stbr_info, j, i - stbr_info->horizontal_contributors[j].n0);
total += coefficient;
}
else if (i < stbr_info->horizontal_contributors[j].n0)
break;
}
STBR_DEBUG_ASSERT(stbr_info->type == STBR_TYPE_UINT8); // Assert below should be 1 + 1/(2^n-1) where n is bits per int.
STBR_DEBUG_ASSERT(total > 0.9f);
STBR_DEBUG_ASSERT(total <= 1.0f + 1.0f / 255);
}
}
#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.
static void stbr__calculate_horizontal_filters(stbr__info* stbr_info)
@ -504,7 +539,7 @@ static void stbr__calculate_horizontal_filters(stbr__info* stbr_info)
}
else
{
float in_pixels_radius = stbr__filter_info_table[stbr_info->filter].support / scale_ratio;
float in_pixels_radius = stbr__filter_info_table[stbr_info->filter].support;
// Looping through in texels
for (n = 0; n < total_contributors; n++)
@ -517,6 +552,10 @@ static void stbr__calculate_horizontal_filters(stbr__info* stbr_info)
stbr__calculate_coefficients_downsample(stbr_info, scale_ratio, out_first_texel, out_last_texel, out_center_of_in, stbr__get_contributor(stbr_info, n), stbr__get_coefficient(stbr_info, n, 0));
}
#ifdef STBR_DEBUG
stbr__check_downsample_coefficients(stbr_info);
#endif
}
}
@ -805,11 +844,7 @@ static void stbr__resample_vertical_upsample(stbr__info* stbr_info, int n, int i
}
for (c = 0; c < channels; c++)
{
STBR_DEBUG_ASSERT(encode_buffer[c] < 1.0f + 1.0f/255);
((unsigned char*)output_data)[out_texel_index + c] = (unsigned char)(encode_buffer[c] * 255);
}
((unsigned char*)output_data)[out_texel_index + c] = (unsigned char)(stbr__saturate(encode_buffer[c]) * 255);
}
}
@ -943,11 +978,7 @@ static void stbr__empty_ring_buffer(stbr__info* stbr_info, int first_necessary_s
int ring_texel_index = texel_index;
int output_texel_index = output_row + texel_index;
for (c = 0; c < channels; c++)
{
//STBR_DEBUG_ASSERT(ring_buffer_entry[ring_texel_index + c] < 1.0f + 1.0f / 255);
((unsigned char*)output_data)[output_texel_index + c] = (unsigned char)(ring_buffer_entry[ring_texel_index + c] * 255);
}
((unsigned char*)output_data)[output_texel_index + c] = (unsigned char)(stbr__saturate(ring_buffer_entry[ring_texel_index + c]) * 255);
}
}
@ -973,7 +1004,7 @@ 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 / scale_ratio;
float in_pixels_radius = stbr__filter_info_table[stbr_info->filter].support;
int max_y = stbr_info->input_h + stbr__get_filter_texel_margin(stbr_info->filter);
STBR_DEBUG_ASSERT(!stbr__use_height_upsampling(stbr_info));