OpenCV4萌新之路——详解图像读取函数 “imread”
处理图像第一步固然是要读取一张图像，OpenCV给出的方法也很简单：
Mat cv::imread(const String& filename, int flags = IMREAD_COLOR);
1、函数简析
头文件 #include <opencv2/imgcodecs.hpp>html
| imread | 返回类型 | 命名空间 | 函数名 | 参数1 | 参数2 |
|---|---|---|---|---|---|
| 详细 | Mat | cv | imread | const String& filename | int flags = IMREAD_COLOR |
| 详细 | - | - | - | 文件路径+文件名 | 图像读取模式 |
2、参数详解
1.String& filename
输入可为相对路径也可为绝对路径，运用方法参见测试代码。ios
注：
imread函数支持读取的图像格式有
Windows bitmaps - *.bmp, *.dib (always supported)
JPEG files - *.jpeg, *.jpg, *.jpe (see the Note section)
JPEG 2000 files - *.jp2 (see the Note section)
Portable Network Graphics - *.png (see the Note section)
WebP - *.webp (see the Note section)
Portable image format - *.pbm, *.pgm, *.ppm *.pxm, *.pnm (always supported)
PFM files - *.pfm (see the Note section)
Sun rasters - *.sr, *.ras (always supported)
TIFF files - *.tiff, *.tif (see the Note section)
OpenEXR Image files - *.exr (see the Note section)
Radiance HDR - *.hdr, *.pic (always supported)
Raster and Vector geospatial data supported by GDAL (see the Note section)
web
2.flags = IMREAD_COLOR
| 值 | 枚举名 | 定义 | 解释 |
|---|---|---|---|
| -1 | IMREAD_UNCHANGED | If set, return the loaded image as is (with alpha channel, otherwise it gets cropped). Ignore EXIF orientation. | 若是设置，则按原样返回加载的图像（使用Alpha通道，不然会被裁剪） |
| 0 | IMREAD_GRAYSCALE | If set, always convert image to the single channel grayscale image (codec internal conversion). | 若是设置，则始终将图像转换为单通道灰度图像（编解码器内部转换） |
| 1 | IMREAD_COLOR | If set, always convert image to the 3 channel BGR color image. | 若是设置，请始终将图像转换为3通道BGR彩色图像 |
| 2 | IMREAD_ANYDEPTH | If set, return 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit. | 若是设置，则在输入具备相应深度时返回16位/ 32位图像，不然将其转换为8位 |
| 4 | IMREAD_ANYCOLOR | If set, the image is read in any possible color format. | 若是设置，则以任何可能的颜色格式读取图像 |
| 8 | IMREAD_LOAD_GDAL | If set, use the gdal driver for loading the image. | 若是设置，使用gdal驱动程序加载图像 |
| 16 | IMREAD_REDUCED_GRAYSCALE_2 | If set, always convert image to the single channel grayscale image and the image size reduced 1/2. | 若是设置，则始终将图像转换为单通道灰度图像，图像尺寸减少1/2 |
| 17 | IMREAD_REDUCED_COLOR_2 | If set, always convert image to the 3 channel BGR color image and the image size reduced 1/2. | 若是设置，则始终将图像转换为3通道BGR彩色图像，图像尺寸减少1/2 |
| 32 | IMREAD_REDUCED_GRAYSCALE_4 | If set, always convert image to the single channel grayscale image and the image size reduced 1/4. | 若是设置，则始终将图像转换为单通道灰度图像，图像尺寸减少1/4 |
| 33 | IMREAD_REDUCED_COLOR_4 | If set, always convert image to the 3 channel BGR color image and the image size reduced 1/4. | 若是设置，则始终将图像转换为3通道BGR彩色图像，图像尺寸减少1/4 |
| 64 | IMREAD_REDUCED_GRAYSCALE_8 | If set, always convert image to the single channel grayscale image and the image size reduced 1/8. | 若是设置，则始终将图像转换为单通道灰度图像，图像尺寸减少1/8 |
| 65 | IMREAD_REDUCED_COLOR_8 | If set, always convert image to the 3 channel BGR color image and the image size reduced 1/8. | 若是设置，则始终将图像转换为3通道BGR彩色图像，图像尺寸减少1/8 |
| 128 | IMREAD_IGNORE_ORIENTATION | If set, do not rotate the image according to EXIF’s orientation flag. | 若是设置，请不要根据EXIF的方向标志旋转图像 |
3、测试代码
#include<iostream> #include<opencv2/opencv.hpp> using namespace cv; using namespace std; #define IMAGE_ABSOLUTE_PATH "F:/Leraning_OpenCV4/Sakai_Izumi.jpg" //绝对路径 #define IMAGE_RELATIVE_PATH "./Sakai_Izumi.jpg" //相对路径 int main() { //读取图片 Mat src = imread(IMAGE_ABSOLUTE_PATH, IMREAD_COLOR); //Mat src = imread(IMAGE_RELATIVE_PATH, 1); //判读是否成功读取图片 if (src.empty()) { std::cout << "Load img failed!" << endl; return 0; } else { std::cout << "Load img success!" << endl; } //显示图片 imshow("src", src); waitKey(0); return 1; }
1. 输入图像参数
2. 输出图像显示
3. 图像参数
4. 其余测试
ImreadModes 0 读取灰度图
ImreadModes 16 读取灰度图，宽、高都为原图的1/2
你们能够参考IMREAD_COLOR中不一样的图像读取模式，对比一下显示图像，体会一下差别在哪。
函数