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Avoid repeated adds and ensure correct round-trip result.

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This commit is contained in:
Jorge Rodriguez 2014-09-09 21:57:46 -07:00
parent f2102d906f
commit 41e6aad693
2 changed files with 22 additions and 11 deletions
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28
stb_image_resize.h
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@ -499,16 +499,25 @@ static unsigned char stbir__linear_to_srgb_uchar(float f)
{ {
int x = (int) (f * (1 << 28)); // has headroom so you don't need to clamp int x = (int) (f * (1 << 28)); // has headroom so you don't need to clamp
int v = 0; int v = 0;
int i;
if (x >= stbir__srgb_offset_to_linear_scaled[ v+128 ]) v += 128; // Everything below 128 is off by 1. This fixes that.
if (x >= stbir__srgb_offset_to_linear_scaled[ v+ 64 ]) v += 64; int fix = 0;
if (x >= stbir__srgb_offset_to_linear_scaled[ v+ 32 ]) v += 32;
if (x >= stbir__srgb_offset_to_linear_scaled[ v+ 16 ]) v += 16; // Adding 1 to 0 with the fix gives incorrect results for input 0. This fixes that.
if (x >= stbir__srgb_offset_to_linear_scaled[ v+ 8 ]) v += 8; if (x < 81000)
if (x >= stbir__srgb_offset_to_linear_scaled[ v+ 4 ]) v += 4; return 0;
if (x >= stbir__srgb_offset_to_linear_scaled[ v+ 2 ]) v += 2;
if (x >= stbir__srgb_offset_to_linear_scaled[ v+ 1 ]) v += 1; i = 128; if (x >= stbir__srgb_offset_to_linear_scaled[i]) v = i; else fix = 1;
return (unsigned char) v; i = v + 64; if (x >= stbir__srgb_offset_to_linear_scaled[i]) v = i;
i = v + 32; if (x >= stbir__srgb_offset_to_linear_scaled[i]) v = i;
i = v + 16; if (x >= stbir__srgb_offset_to_linear_scaled[i]) v = i;
i = v + 8; if (x >= stbir__srgb_offset_to_linear_scaled[i]) v = i;
i = v + 4; if (x >= stbir__srgb_offset_to_linear_scaled[i]) v = i;
i = v + 2; if (x >= stbir__srgb_offset_to_linear_scaled[i]) v = i;
i = v + 1; if (x >= stbir__srgb_offset_to_linear_scaled[i]) v = i;
return (unsigned char)v + fix;
} }
static float stbir__filter_box(float x) static float stbir__filter_box(float x)
@ -1246,7 +1255,6 @@ static void stbir__encode_scanline(stbir__info* stbir_info, int num_pixels, void
int output_pixel_index = x*channels; int output_pixel_index = x*channels;
int encode_pixel_index = x*channels; int encode_pixel_index = x*channels;
for (n = 0; n < channels; n++) for (n = 0; n < channels; n++)
((unsigned char*)output_buffer)[output_pixel_index + n] = stbir__linear_to_srgb_uchar(encode_buffer[encode_pixel_index + n]); ((unsigned char*)output_buffer)[output_pixel_index + n] = stbir__linear_to_srgb_uchar(encode_buffer[encode_pixel_index + n]);

3
tests/resample_test.cpp
View File

@ -734,6 +734,9 @@ void test_suite(int argc, char **argv)
} }
#endif #endif
for (i = 0; i < 256; 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) { for (i=0; i < 256; ++i) {
float f = stbir__srgb_to_linear((i+0.5f)/256.0f); float f = stbir__srgb_to_linear((i+0.5f)/256.0f);