質問編集履歴
2
誤字の修正
test
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test
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@@ -152,11 +152,11 @@
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na = 0;
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nr =
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nr = max_val;
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ng =
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ng = max_val;
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nb =
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nb = max_val;
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} else {
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1
参考プログラム例示
test
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test
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@@ -27,3 +27,163 @@
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27
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よろしくお願い致します。
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30
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31
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32
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まず png ファイルを ppm ファイルにしておき、以下のようなプログラムで、ppm ファイルから 色情報の ppm と、アルファチャンネルの pgm を生成、最後に、それらを結合して透過 png を生成…としてみることはできました。
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もっといい方法があれば、教えて下さい。
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```lang-bash
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filename="a.png"
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40
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base=`basename $filename .png`
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pngtopam $filename | pamtopnm -plain > ${base}.ppm
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./pnmalpha ${base}.ppm ${base}_col.ppm ${base}_alpha.pgm
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46
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pnmtopng -force -alpha=${base}_alpha.pgm ${base}_col.ppm > ${base}_trans.png
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48
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49
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```
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50
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```lang-C++
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53
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#include<iostream>
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54
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#include<fstream>
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56
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57
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#include<algorithm>
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58
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59
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60
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61
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int main(int argc, char **argv) {
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62
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63
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if (argc < 4) {
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64
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65
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std::cout << "too few arguments" << std::endl;
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66
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std::cout << "usage: src.ppm dst.ppm alpha.pgm" << std::endl;
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68
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return 1;
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70
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}
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const std::string magic_ppm = "P3", magic_pgm = "P2";
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76
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77
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std::string magic;
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std::ifstream ifs(argv[1]);
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80
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81
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std::ofstream ofs_color(argv[2]), ofs_alpha(argv[3]);
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82
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83
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int w, h, max_val;
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84
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85
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int r, g, b, min_rgb; // current val
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86
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87
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int nr, ng, nb, na; // new val
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88
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89
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90
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91
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if (!ifs || !ofs_color || !ofs_alpha) {
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92
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93
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std::cerr << "file open error" << std::endl;
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94
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return 1;
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96
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}
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100
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ifs >> magic;
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102
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103
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if (magic != magic_ppm) {
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104
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105
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std::cerr << "input file format error" << std::endl;
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106
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return 1;
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}
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110
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111
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ifs >> w >> h;
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112
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113
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ifs >> max_val;
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115
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116
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ofs_color << magic_ppm << std::endl;
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ofs_color << w << " " << h << std::endl;
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ofs_color << max_val << std::endl;
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123
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124
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125
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ofs_alpha << magic_pgm << std::endl;
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127
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ofs_alpha << w << " " << h << std::endl;
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128
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129
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ofs_alpha << max_val << std::endl;
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130
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131
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132
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133
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for (int i = 0; i < h; ++i) {
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135
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for (int j = 0; j < w; ++j) {
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136
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137
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ifs >> r >> g >> b;
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138
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139
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min_rgb = std::min(r, std::min(g, b));
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140
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+
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141
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+
if (min_rgb == 0) {
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142
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143
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na = max_val;
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144
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145
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nr = r;
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146
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+
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147
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ng = g;
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148
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+
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149
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nb = b;
|
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150
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+
|
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151
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+
} else if (min_rgb == max_val) {
|
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152
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+
|
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153
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+
na = 0;
|
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154
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+
|
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155
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+
nr = 128;
|
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156
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+
|
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157
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+
ng = 128;
|
|
158
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+
|
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159
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+
nb = 128;
|
|
160
|
+
|
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161
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+
} else {
|
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162
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+
|
|
163
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+
na = max_val - min_rgb;
|
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164
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+
|
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165
|
+
nr = (r + na - max_val) * max_val / na;
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166
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+
|
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167
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+
ng = (g + na - max_val) * max_val / na;
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168
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+
|
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169
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+
nb = (b + na - max_val) * max_val / na;
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170
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+
|
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171
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+
}
|
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172
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+
|
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173
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+
ofs_color << nr << " " << ng << " " << nb << " ";
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174
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+
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175
|
+
ofs_alpha << na << " ";
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176
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+
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177
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+
}
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178
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+
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179
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+
ofs_color << std::endl;
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180
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+
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181
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+
ofs_alpha << std::endl;
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182
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+
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183
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+
}
|
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184
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+
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185
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+
return 0;
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186
|
+
|
|
187
|
+
}
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188
|
+
|
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189
|
+
```
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