1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
|
#include "imagescaler.h"
#include <cstdlib>
#include <cmath>
ImageScaler::ImageScaler() :
m_memory(NULL),
m_hor_filters(NULL),
m_ver_filters(NULL),
m_buffer(NULL),
m_dst_image(NULL),
m_dst_stride(0),
m_dst_width(0),
m_dst_height(0),
m_src_width(0),
m_src_height(0),
m_src_x(0),
m_src_y(0),
m_dst_x(0),
m_dst_y(0) {
}
ImageScaler::~ImageScaler() {
if ( m_memory ) free( m_memory );
}
// sin(x)/(x)
static float sincf( float x ) {
if ( fabsf(x) < 0.05f ) return 1.0f - (1.0f/6.0f)*x*x; // taylor series approximation to avoid 0/0
return sin(x)/x;
}
static void CalculateFilters( ImageScaler::Filter *filters, int dst_size, int src_size ) {
const float fc = dst_size >= src_size ? 1.0f : ((float) dst_size)/((float) src_size);
for (int i = 0; i < dst_size; i++) {
const int d = 2*dst_size; // sample position denominator
const int e = (2*i+1) * src_size - dst_size; // sample position enumerator
int offset = e / d; // truncated sample position
const float sub_offset = ((float) (e - offset*d)) / ((float) d); // exact sample position is (float) e/d = offset + sub_offset
// calculate filter coefficients
float h[4];
for (int j=0; j<4; j++) {
const float t = 3.14159265359f * (sub_offset+(1-j));
h[j] = sincf( fc * t ) * cosf( 0.25f * t ); // sinc-lowpass and cos-window
}
// ensure that filter does not reach out off image bounds:
while ( offset < 1 ) {
h[0] += h[1];
h[1] = h[2];
h[2] = h[3];
h[3] = 0.0f;
offset++;
}
while ( offset+3 > src_size ) {
h[3] += h[2];
h[2] = h[1];
h[1] = h[0];
h[0] = 0.0f;
offset--;
}
// coefficients are normalized to sum up to 2048
const float norm = 2048.0f / ( h[0] + h[1] + h[2] + h[3] );
offset--; // offset of fist used pixel
filters[i].m_offset = offset + 4; // store offset of first unused pixel
for (int j=0; j<4; j++) {
const float t = norm * h[j];
filters[i].m_coeff[(offset+j) & 3] = (int) ((t > 0.0f) ? (t+0.5f) : (t-0.5f)); // consider ring buffer index permutations
}
}
// set end marker
filters[dst_size].m_offset = (unsigned) -1;
}
void ImageScaler::SetImageParameters( unsigned *dst_image, unsigned dst_stride, unsigned dst_width, unsigned dst_height, unsigned src_width, unsigned src_height ) {
m_src_x = 0;
m_src_y = 0;
m_dst_x = 0;
m_dst_y = 0;
m_dst_image = dst_image;
m_dst_stride = dst_stride;
// if image dimensions do not change we can keep the old filter coefficients
if ( (src_width == m_src_width) && (src_height == m_src_height) && (dst_width == m_dst_width) && (dst_height == m_dst_height) ) return;
m_dst_width = dst_width;
m_dst_height = dst_height;
m_src_width = src_width;
m_src_height = src_height;
if ( m_memory ) free( m_memory );
const unsigned hor_filters_size = (m_dst_width + 1) * sizeof(Filter); // reserve one extra position for end marker
const unsigned ver_filters_size = (m_dst_height + 1) * sizeof(Filter);
const unsigned buffer_size = 4 * m_dst_width * sizeof(TmpPixel);
char *p = (char *) malloc( hor_filters_size + ver_filters_size + buffer_size );
m_memory = p;
m_hor_filters = (Filter *) p; p += hor_filters_size;
m_ver_filters = (Filter *) p; p += ver_filters_size;
m_buffer = (TmpPixel *) p;
CalculateFilters( m_hor_filters, m_dst_width , m_src_width );
CalculateFilters( m_ver_filters, m_dst_height, m_src_height );
}
// shift range to 0..255 and clamp overflows
static unsigned shift_clamp( int x ) {
x = ( x + (1<<21) ) >> 22;
if ( x < 0 ) return 0;
if ( x > 255 ) return 255;
return x;
}
void ImageScaler::NextSourceLine() {
m_dst_x = 0;
m_src_x = 0;
m_src_y++;
while ( m_ver_filters[m_dst_y].m_offset == m_src_y ) {
const int h0 = m_ver_filters[m_dst_y].m_coeff[0];
const int h1 = m_ver_filters[m_dst_y].m_coeff[1];
const int h2 = m_ver_filters[m_dst_y].m_coeff[2];
const int h3 = m_ver_filters[m_dst_y].m_coeff[3];
const TmpPixel *src = m_buffer;
unsigned *dst = m_dst_image + m_dst_stride * m_dst_y;
for (unsigned i=0; i<m_dst_width; i++) {
const ImageScaler::TmpPixel t( src[0]*h0 + src[1]*h1 + src[2]*h2 + src[3]*h3 );
src += 4;
dst[i] = shift_clamp(t[0]) | (shift_clamp(t[1])<<8) | (shift_clamp(t[2])<<16) | (shift_clamp(t[3])<<24);
}
m_dst_y++;
}
}
|
