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Fix upscaling image with bilinear interpolation option specified 

Fix error in calculation of 4 nearest points in source image when
resizing image with bilinear interpolation.

(cherry picked from commit f24ec3878e)
This commit is contained in:
Maganty Rushyendra 2020-06-17 16:26:57 +08:00 committed by Rémi Verschelde
parent 8f28e0861f
commit afac2514f8
1 changed files with 18 additions and 17 deletions
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35
core/image.cpp
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@ -619,34 +619,35 @@ static void _scale_bilinear(const uint8_t *__restrict p_src, uint8_t *__restrict
enum {
FRAC_BITS = 8,
FRAC_LEN = (1 << FRAC_BITS),
FRAC_HALF = (FRAC_LEN >> 1),
FRAC_MASK = FRAC_LEN - 1
};
for (uint32_t i = 0; i < p_dst_height; i++) {
uint32_t src_yofs_up_fp = (i * p_src_height * FRAC_LEN / p_dst_height);
uint32_t src_yofs_frac = src_yofs_up_fp & FRAC_MASK;
uint32_t src_yofs_up = src_yofs_up_fp >> FRAC_BITS;
uint32_t src_yofs_down = (i + 1) * p_src_height / p_dst_height;
if (src_yofs_down >= p_src_height)
// Add 0.5 in order to interpolate based on pixel center
uint32_t src_yofs_up_fp = (i + 0.5) * p_src_height * FRAC_LEN / p_dst_height;
// Calculate nearest src pixel center above current, and truncate to get y index
uint32_t src_yofs_up = src_yofs_up_fp >= FRAC_HALF ? (src_yofs_up_fp - FRAC_HALF) >> FRAC_BITS : 0;
uint32_t src_yofs_down = (src_yofs_up_fp + FRAC_HALF) >> FRAC_BITS;
if (src_yofs_down >= p_src_height) {
src_yofs_down = p_src_height - 1;
//src_yofs_up*=CC;
//src_yofs_down*=CC;
}
// Calculate distance to pixel center of src_yofs_up
uint32_t src_yofs_frac = src_yofs_up_fp & FRAC_MASK;
src_yofs_frac = src_yofs_frac >= FRAC_HALF ? src_yofs_frac - FRAC_HALF : src_yofs_frac + FRAC_HALF;
uint32_t y_ofs_up = src_yofs_up * p_src_width * CC;
uint32_t y_ofs_down = src_yofs_down * p_src_width * CC;
for (uint32_t j = 0; j < p_dst_width; j++) {
uint32_t src_xofs_left_fp = (j * p_src_width * FRAC_LEN / p_dst_width);
uint32_t src_xofs_frac = src_xofs_left_fp & FRAC_MASK;
uint32_t src_xofs_left = src_xofs_left_fp >> FRAC_BITS;
uint32_t src_xofs_right = (j + 1) * p_src_width / p_dst_width;
if (src_xofs_right >= p_src_width)
uint32_t src_xofs_left_fp = (j + 0.5) * p_src_width * FRAC_LEN / p_dst_width;
uint32_t src_xofs_left = src_xofs_left_fp >= FRAC_HALF ? (src_xofs_left_fp - FRAC_HALF) >> FRAC_BITS : 0;
uint32_t src_xofs_right = (src_xofs_left_fp + FRAC_HALF) >> FRAC_BITS;
if (src_xofs_right >= p_src_width) {
src_xofs_right = p_src_width - 1;
}
uint32_t src_xofs_frac = src_xofs_left_fp & FRAC_MASK;
src_xofs_frac = src_xofs_frac >= FRAC_HALF ? src_xofs_frac - FRAC_HALF : src_xofs_frac + FRAC_HALF;
src_xofs_left *= CC;
src_xofs_right *= CC;