实验需要，加上好奇，使用libpng库将png文件的背景，由黑色，替换成无背景颜色。效果如下图：
替换前：
替换后：
黑色背景都没了，只剩下白色了，看不出来。。。。。。
步骤：
1. 下载png相关库，libpng，以及zlib压缩解压缩文件
libpng官网下载，Ubuntu下zlib下载安装: sudo apt-get install zlib1-dev
2. 代码：
1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <string.h>
4 #include <png.h>
5
6
7 #define PNG_BYTES_TO_CHECK 8
8 #define HAVE_ALPHA 1
9 #define NOT_HAVE_ALPHA 0
10
11 typedef struct _pic_data pic_data;
12 struct _pic_data {
13 int width, height; //长宽
14 int bit_depth; //位深度
15 int alpha_flag; //是否有透明通道
16 unsigned char *rgba;//实际rgb数据
17 };
18
19 int check_is_png(FILE **fp, const char *filename) //检查是否png文件
20 {
21 char checkheader[PNG_BYTES_TO_CHECK]; //查询是否png头
22 *fp = fopen(filename, "rb");
23 if (*fp == NULL) {
24 printf("open failed ...1\n");
25 return -1;
26 }
27 if (fread(checkheader, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK) //读取png文件长度错误直接退出
28 return 0;
29 return png_sig_cmp(checkheader, 0, PNG_BYTES_TO_CHECK); //0正确, 非0错误
30 }
31
32 int decode_png(const char *filename, pic_data *out) //取出png文件中的rgb数据
33 {
34 png_structp png_ptr; //png文件句柄
35 png_infop info_ptr;//png图像信息句柄
36 int ret;
37 FILE *fp;
38 if (check_is_png(&fp, filename) != 0) {
39 printf("file is not png ...\n");
40 return -1;
41 }
42 printf("launcher[%s] ...\n", PNG_LIBPNG_VER_STRING); //打印当前libpng版本号
43
44 //1: 初始化libpng的数据结构 :png_ptr, info_ptr
45 png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
46 info_ptr = png_create_info_struct(png_ptr);
47
48 //2: 设置错误的返回点
49 setjmp(png_jmpbuf(png_ptr));
50 rewind(fp); //等价fseek(fp, 0, SEEK_SET);
51
52 //3: 把png结构体和文件流io进行绑定
53 png_init_io(png_ptr, fp);
54 //4:读取png文件信息以及强转转换成RGBA:8888数据格式
55 png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0); //读取文件信息
56 int channels, color_type;
57 channels = png_get_channels(png_ptr, info_ptr); //通道数量
58 color_type = png_get_color_type(png_ptr, info_ptr);//颜色类型
59 out->bit_depth = png_get_bit_depth(png_ptr, info_ptr);//位深度
60 out->width = png_get_image_width(png_ptr, info_ptr);//宽
61 out->height = png_get_image_height(png_ptr, info_ptr);//高
62
63 //if(color_type == PNG_COLOR_TYPE_PALETTE)
64 // png_set_palette_to_rgb(png_ptr);//要求转换索引颜色到RGB
65 //if(color_type == PNG_COLOR_TYPE_GRAY && out->bit_depth < 8)
66 // png_set_expand_gray_1_2_4_to_8(png_ptr);//要求位深度强制8bit
67 //if(out->bit_depth == 16)
68 // png_set_strip_16(png_ptr);//要求位深度强制8bit
69 //if(png_get_valid(png_ptr,info_ptr,PNG_INFO_tRNS))
70 // png_set_tRNS_to_alpha(png_ptr);
71 //if(color_type == PNG_COLOR_TYPE_GRAY || color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
72 // png_set_gray_to_rgb(png_ptr);//灰度必须转换成RG
73 printf("channels = %d color_type = %d bit_depth = %d width = %d height = %d ...\n",
74 channels, color_type, out->bit_depth, out->width, out->height);
75
76 int i, j, k;
77 int size, pos = 0;
78 int temp;
79
80 //5: 读取实际的rgb数据
81 png_bytepp row_pointers; //实际存储rgb数据的buf
82 row_pointers = png_get_rows(png_ptr, info_ptr); //也可以分别每一行获取png_get_rowbytes();
83 size = out->width * out->height; //申请内存先计算空间
84 if (channels == 4 || color_type == PNG_COLOR_TYPE_RGB_ALPHA) { //判断是24位还是32位
85 out->alpha_flag = HAVE_ALPHA; //记录是否有透明通道
86 size *= (sizeof(unsigned char) * 4); //size = out->width * out->height * channel
87 out->rgba = (png_bytep)malloc(size);
88 if (NULL == out->rgba) {
89 printf("malloc rgba faile ...\n");
90 png_destroy_read_struct(&png_ptr, &info_ptr, 0);
91 fclose(fp);
92 return -1;
93 }
94 //从row_pointers里读出实际的rgb数据出来
95 temp = channels - 1;
96 for (i = 0; i < out->height; i++)
97 for (j = 0; j < out->width * 4; j += 4)
98 for (k = temp; k >= 0; k--)
99 out->rgba[pos++] = row_pointers[i][j + k];
100 } else if (channels == 3 || color_type == PNG_COLOR_TYPE_RGB) { //判断颜色深度是24位还是32位
101 out->alpha_flag = NOT_HAVE_ALPHA;
102 size *= (sizeof(unsigned char) * 3);
103 out->rgba = (png_bytep)malloc(size);
104 if (NULL == out->rgba) {
105 printf("malloc rgba faile ...\n");
106 png_destroy_read_struct(&png_ptr, &info_ptr, 0);
107 fclose(fp);
108 return -1;
109 }
110 //从row_pointers里读出实际的rgb数据
111 temp = (3 * out->width);
112 for (i = 0; i < out->height; i ++) {
113 for (j = 0; j < temp; j += 3) {
114 out->rgba[pos++] = row_pointers[i][j+2];
115 out->rgba[pos++] = row_pointers[i][j+1];
116 out->rgba[pos++] = row_pointers[i][j+0];
117 }
118 }
119 } else return -1;
120 //6:销毁内存
121 png_destroy_read_struct(&png_ptr, &info_ptr, 0);
122 fclose(fp);
123 //此时， 我们的out->rgba里面已经存储有实际的rgb数据了
124 //处理完成以后free(out->rgba)
125 return 0;
126 }
127
128 int RotationRight90(unsigned char * src, int srcW, int srcH, int channel) //顺时针旋转90度
129 {
130 unsigned char * tempSrc = NULL; //临时的buf用来记录原始的图像(未旋转之前的图像)
131 int mSize = srcW * srcH * sizeof(char) * channel;
132 int i = 0;
133 int j = 0;
134 int k = 0;
135 int l = 3;
136 int desW = 0;
137 int desH = 0;
138
139 desW = srcH;
140 desH = srcW;
141
142 tempSrc = (unsigned char *)malloc(sizeof(char) * srcW * srcH * channel);
143 memcpy(tempSrc, src, mSize); //拷贝原始图像至tempbuf
144 for(i = 0; i < desH; i ++)
145 {
146 for(j = 0; j < desW; j ++)
147 {
148 for(k = 0; k < channel; k ++)
149 {
150 src[(i * desW + j) * channel + k] = tempSrc[((srcH - 1 - j) * srcW + i) * channel + k]; //替换像素
151 }
152 }
153 }
154 free(tempSrc);
155 return 0;
156 }
157
158 int write_png_file(const char *filename , pic_data *out) //生成一个新的png图像
159 {
160 png_structp png_ptr;
161 png_infop info_ptr;
162 png_byte color_type;
163 png_bytep * row_pointers;
164 FILE *fp = fopen(filename, "wb");
165 if (NULL == fp) {
166 printf("open failed ...2\n");
167 return -1;
168 }
169 //1: 初始化libpng结构体
170 png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);
171 if (!png_ptr) {
172 printf("png_create_write_struct failed ...\n");
173 return -1;
174 }
175 //2: 初始化png_infop结构体 ，
176 //此结构体包含了图像的各种信息如尺寸，像素位深, 颜色类型等等
177 info_ptr = png_create_info_struct(png_ptr);
178 if (!info_ptr) {
179 printf("png_create_info_struct failed ...\n");
180 return -1;
181 }
182 //3: 设置错误返回点
183 if (setjmp(png_jmpbuf(png_ptr))) {
184 printf("error during init_io ...\n");
185 return -1;
186 }
187 //4:绑定文件IO到Png结构体
188 png_init_io(png_ptr, fp);
189 if (setjmp(png_jmpbuf(png_ptr))) {
190 printf("error during init_io ...\n");
191 return -1;
192 }
193 if (out->alpha_flag == HAVE_ALPHA) color_type = PNG_COLOR_TYPE_RGB_ALPHA;
194 else color_type = PNG_COLOR_TYPE_RGB;
195 //5：设置以及写入头部信息到Png文件
196 png_set_IHDR(png_ptr, info_ptr, out->width, out->height, out->bit_depth,
197 PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
198 png_write_info(png_ptr, info_ptr);
199 if (setjmp(png_jmpbuf(png_ptr))) {
200 printf("error during init_io ...\n");
201 return -1;
202 }
203 int channels, temp;
204 int i, j, pos = 0;
205 if (out->alpha_flag == HAVE_ALPHA) {
206 channels = 4;
207 temp = (4 * out->width);
208 printf("have alpha ...\n");
209 } else {
210 channels = 4;
211 temp = (4 * out->width);
212 printf("not have alpha ...\n");
213 }
214 // 顺时针旋转90度 ， 旋转完了一定要把width 和height调换 不然得到的图像是花的 旋转三次就是逆时针旋转一次
215 //RotationRight90(out->rgba, out->width, out->height, channels);
216 //RotationRight90(out->rgba, out->height, out->width, channels);
217 //RotationRight90(out->rgba, out->width, out->height, channels);
218 row_pointers = (png_bytep*)malloc(out->height * sizeof(png_bytep));
219 for (i = 0; i < out->height; i++) {
220 row_pointers[i] = (png_bytep)malloc(temp* sizeof(unsigned char));
221 for (j = 0; j < temp; j += channels) {
222 if (channels == 4) {
223 if (out->alpha_flag == HAVE_ALPHA)
224 row_pointers[i][j+3] = out->rgba[pos++];
225 //row_pointers[i][j+3] = 0x00;
226 row_pointers[i][j+2] = out->rgba[pos++];
227 row_pointers[i][j+1] = out->rgba[pos++];
228 row_pointers[i][j+0] = out->rgba[pos++];
229 //printf("---- i = %d, j = %d, %d, %d, %d, %d\n", i, j, row_pointers[i][j + 0], row_pointers[i][j + 1],row_pointers[i][j + 2],row_pointers[i][j + 3]);
230 if((row_pointers[i][j+0] + row_pointers[i][j+1] + row_pointers[i][j+2]) < 100)
231 {
232 row_pointers[i][j+3] = 0x00;
233 row_pointers[i][j+2] = 0x00;
234 row_pointers[i][j+1] = 0x00;
235 row_pointers[i][j+0] = 0x00;
236
237 }
238 else
239 {
240 row_pointers[i][j+3] = 0xff;
241 row_pointers[i][j+2] = 0xff;
242 row_pointers[i][j+1] = 0xff;
243 row_pointers[i][j+0] = 0xff;
244 }
245 //printf("---- i = %d, j = %d, %d, %d, %d, %d\n", i, j, row_pointers[i][j + 0], row_pointers[i][j + 1],row_pointers[i][j + 2],row_pointers[i][j + 3]);
246 } else {
247 row_pointers[i][j+2] = out->rgba[pos++];
248 row_pointers[i][j+1] = out->rgba[pos++];
249 row_pointers[i][j+0] = out->rgba[pos++];
250 if((row_pointers[i][j+0] + row_pointers[i][j+1] + row_pointers[i][j+2]) < 30)
251 {
252 row_pointers[i][j+3] = 0x00;
253 row_pointers[i][j+2] = 0x00;
254 row_pointers[i][j+1] = 0x00;
255 row_pointers[i][j+0] = 0x00;
256
257 }
258 else
259 {
260 row_pointers[i][j+3] = 0xff;
261 row_pointers[i][j+2] = 0xff;
262 row_pointers[i][j+1] = 0xff;
263 row_pointers[i][j+0] = 0xff;
264 }
265 // printf("++++ i = %d, j = %d, %d, %d, %d, %d\n", i, j, row_pointers[i][j + 0], row_pointers[i][j + 1],row_pointers[i][j + 2],row_pointers[i][j + 3]);
266 }
267 }
268 }
269 //6: 写入rgb数据到Png文件
270 png_write_image(png_ptr, (png_bytepp)row_pointers);
271 if (setjmp(png_jmpbuf(png_ptr))) {
272 printf("error during init_io ...\n");
273 return -1;
274 }
275 //7: 写入尾部信息
276 png_write_end(png_ptr, NULL);
277 //8:释放内存 ,销毁png结构体
278 for (i = 0; i < out->height; i ++)
279 free(row_pointers[i]);
280 free(row_pointers);
281 png_destroy_write_struct(&png_ptr, &info_ptr);
282 fclose(fp);
283 return 0;
284 }
285
286 int main(int argc, char **argv)
287 {
288 pic_data out;
289 if (argc == 3) {
290 decode_png(argv[1], &out);
291 write_png_file(argv[2], &out);
292 free(out.rgba);
293 } else {
294 puts("please input two file, \nargv[1]:source.png argv[2]:dest.png");
295 }
296 return 0;
297 }
参考：https://blog.csdn.net/wang93IT/article/details/85003730
原文地址：https://www.cnblogs.com/hanrp/p/11419147.html
时间： 2024-10-09 07:28:07