1### opencv to ncnn
2
3* cv::Mat CV_8UC3 -> ncnn::Mat 3 channel + swap RGB/BGR
4
5```cpp
6// cv::Mat a(h, w, CV_8UC3);
7ncnn::Mat in = ncnn::Mat::from_pixels(a.data, ncnn::Mat::PIXEL_BGR2RGB, a.cols, a.rows);
8```
9
10* cv::Mat CV_8UC3 -> ncnn::Mat 3 channel + keep RGB/BGR order
11
12```cpp
13// cv::Mat a(h, w, CV_8UC3);
14ncnn::Mat in = ncnn::Mat::from_pixels(a.data, ncnn::Mat::PIXEL_RGB, a.cols, a.rows);
15```
16
17* cv::Mat CV_8UC3 -> ncnn::Mat 1 channel + do RGB2GRAY/BGR2GRAY
18
19```cpp
20// cv::Mat rgb(h, w, CV_8UC3);
21ncnn::Mat inrgb = ncnn::Mat::from_pixels(rgb.data, ncnn::Mat::PIXEL_RGB2GRAY, rgb.cols, rgb.rows);
22
23// cv::Mat bgr(h, w, CV_8UC3);
24ncnn::Mat inbgr = ncnn::Mat::from_pixels(bgr.data, ncnn::Mat::PIXEL_BGR2GRAY, bgr.cols, bgr.rows);
25```
26
27* cv::Mat CV_8UC1 -> ncnn::Mat 1 channel
28
29```cpp
30// cv::Mat a(h, w, CV_8UC1);
31ncnn::Mat in = ncnn::Mat::from_pixels(a.data, ncnn::Mat::PIXEL_GRAY, a.cols, a.rows);
32```
33
34* cv::Mat CV_32FC1 -> ncnn::Mat 1 channel
35
36  * **You could construct ncnn::Mat and fill data into it directly to avoid data copy**
37
38```cpp
39// cv::Mat a(h, w, CV_32FC1);
40ncnn::Mat in(a.cols, a.rows, 1, (void*)a.data);
41in = in.clone();
42```
43
44* cv::Mat CV_32FC3 -> ncnn::Mat 3 channel
45
46  * **You could construct ncnn::Mat and fill data into it directly to avoid data copy**
47
48```cpp
49// cv::Mat a(h, w, CV_32FC3);
50ncnn::Mat in_pack3(a.cols, a.rows, 1, (void*)a.data, (size_t)4u * 3, 3);
51ncnn::Mat in;
52ncnn::convert_packing(in_pack3, in, 1);
53```
54
55* std::vector < cv::Mat > + CV_32FC1 -> ncnn::Mat multiple channels
56
57  * **You could construct ncnn::Mat and fill data into it directly to avoid data copy**
58
59```cpp
60// std::vector<cv::Mat> a(channels, cv::Mat(h, w, CV_32FC1));
61int channels = a.size();
62ncnn::Mat in(a[0].cols, a[0].rows, channels);
63for (int p=0; p<in.c; p++)
64{
65    memcpy(in.channel(p), (const uchar*)a[p].data, in.w * in.h * sizeof(float));
66}
67```
68
69### ncnn to opencv
70
71* ncnn::Mat 3 channel -> cv::Mat CV_8UC3 + swap RGB/BGR
72
73  * **You may need to call in.substract_mean_normalize() first to scale values from 0..1 to 0..255**
74
75```cpp
76// ncnn::Mat in(w, h, 3);
77cv::Mat a(in.h, in.w, CV_8UC3);
78in.to_pixels(a.data, ncnn::Mat::PIXEL_BGR2RGB);
79```
80
81* ncnn::Mat 3 channel -> cv::Mat CV_8UC3 + keep RGB/BGR order
82
83  * **You may need to call in.substract_mean_normalize() first to scale values from 0..1 to 0..255**
84
85```cpp
86// ncnn::Mat in(w, h, 3);
87cv::Mat a(in.h, in.w, CV_8UC3);
88in.to_pixels(a.data, ncnn::Mat::PIXEL_RGB);
89```
90
91* ncnn::Mat 1 channel -> cv::Mat CV_8UC1
92
93  * **You may need to call in.substract_mean_normalize() first to scale values from 0..1 to 0..255**
94
95```cpp
96// ncnn::Mat in(w, h, 1);
97cv::Mat a(in.h, in.w, CV_8UC1);
98in.to_pixels(a.data, ncnn::Mat::PIXEL_GRAY);
99```
100
101* ncnn::Mat 1 channel -> cv::Mat CV_32FC1
102
103  * **You could consume or manipulate ncnn::Mat data directly to avoid data copy**
104
105```cpp
106// ncnn::Mat in;
107cv::Mat a(in.h, in.w, CV_32FC1);
108memcpy((uchar*)a.data, in.data, in.w * in.h * sizeof(float));
109```
110
111* ncnn::Mat 3 channel -> cv::Mat CV_32FC3
112
113  * **You could consume or manipulate ncnn::Mat data directly to avoid data copy**
114
115```cpp
116// ncnn::Mat in(w, h, 3);
117ncnn::Mat in_pack3;
118ncnn::convert_packing(in, in_pack3, 3);
119cv::Mat a(in.h, in.w, CV_32FC3);
120memcpy((uchar*)a.data, in_pack3.data, in.w * in.h * 3 * sizeof(float));
121```
122
123* ncnn::Mat multiple channels -> std::vector < cv::Mat > + CV_32FC1
124
125  * **You could consume or manipulate ncnn::Mat data directly to avoid data copy**
126
127```cpp
128// ncnn::Mat in(w, h, channels);
129std::vector<cv::Mat> a(in.c);
130for (int p=0; p<in.c; p++)
131{
132    a[p] = cv::Mat(in.h, in.w, CV_32FC1);
133    memcpy((uchar*)a[p].data, in.channel(p), in.w * in.h * sizeof(float));
134}
135```
136