From f24ec3878efac4f425a822b9910673f5939629b9 Mon Sep 17 00:00:00 2001 From: Maganty Rushyendra Date: Wed, 17 Jun 2020 16:26:57 +0800 Subject: [PATCH] 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. --- core/image.cpp | 27 ++++++++++++++------------- 1 file changed, 14 insertions(+), 13 deletions(-) diff --git a/core/image.cpp b/core/image.cpp index 0f15574053b..45f10625a9f 100644 --- a/core/image.cpp +++ b/core/image.cpp @@ -678,34 +678,35 @@ 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; + // 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; + 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;