ubuntu22.04@laptop OpenCV Get Started: 003_image_resizing
- [1. 源由](#1. 源由)
- [2. resize应用Demo](#2. resize应用Demo)
- [3 image_resize](#3 image_resize)
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- [3.1 C++应用Demo](#3.1 C++应用Demo)
- [3.2 Python应用Demo](#3.2 Python应用Demo)
- [3.3 重点过程分析](#3.3 重点过程分析)
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- [3.3.1 根据宽高调整大小](#3.3.1 根据宽高调整大小)
- [3.3.2 根据比例调整大小](#3.3.2 根据比例调整大小)
- [3.3.3 根据插值方式调整大小](#3.3.3 根据插值方式调整大小)
- [4. 总结](#4. 总结)
- [5. 参考资料](#5. 参考资料)
1. 源由
在OpenCV中调整图像大小：
- 要记住图像的原始纵横比（即宽高比）
- 减小图像的大小，需要对像素缩减采样值。
- 增加图像的大小，需要对新像素进行插值。
各种插值技术开始发挥作用来完成上述操作。
2. resize应用Demo
003_image_resizing是OpenCV调整图像比例的示例程序。
确认OpenCV安装路径：
$ find /home/daniel/ -name "OpenCVConfig.cmake"
/home/daniel/OpenCV/installation/opencv-4.9.0/lib/cmake/opencv4/
/home/daniel/OpenCV/opencv/build/OpenCVConfig.cmake
/home/daniel/OpenCV/opencv/build/unix-install/OpenCVConfig.cmake
$ export OpenCV_DIR=/home/daniel/OpenCV/installation/opencv-4.9.0/lib/cmake/opencv4/
3 image_resize
3.1 C++应用Demo
C++应用Demo工程结构：
003_image_resizing/CPP$ tree .
.
├── CMakeLists.txt
├── image.jpg
└── image_resize.cpp
0 directories, 3 files
C++应用Demo工程编译执行：
$ mkdir build
$ cd build
$ cmake ..
$ cmake --build . --config Release
$ cd ..
$ ./build/image_resize
3.2 Python应用Demo
Python应用Demo工程结构：
003_image_resizing/Python$ tree .
.
├── image.jpg
├── image_resize.py
└── requirements.txt
0 directories, 3 files
Python应用Demo工程执行：
$ workoncv-4.9.0
$ python image_resize.py
3.3 重点过程分析
- src: It is the required input image, it could be a string with the path of the input image (eg: 'test_image.png').
- dsize: It is the desired size of the output image, it can be a new height and width.
- fx: Scale factor along the horizontal axis.
- fy: Scale factor along the vertical axis.
- interpolation: It gives us the option of different methods of resizing the image.
3.3.1 根据宽高调整大小
C++:
// Set rows and columns
int up_width = 600;
int up_height = 400;
Mat resized_up;
//resize up
resize(image, resized_up, Size(up_width, up_height), INTER_LINEAR);
Python:
# Set rows and columns
up_width = 600
up_height = 400
up_points = (up_width, up_height)
# resize the image
resized_up = cv2.resize(image, up_points, interpolation = cv2.INTER_LINEAR)
3.3.2 根据比例调整大小
C++:
// Scaling Up the image 1.2 times by specifying both scaling factors
double scale_up_x = 1.2;
double scale_up_y = 1.2;
// Scaling Down the image 0.6 times specifying a single scale factor.
double scale_down = 0.6;
Mat scaled_f_up, scaled_f_down;
//resize
resize(image,scaled_f_down, Size(), scale_down, scale_down, INTER_LINEAR);
resize(image, scaled_f_up, Size(), scale_up_x, scale_up_y, INTER_LINEAR);
Python:
# Scaling Up the image 1.2 times by specifying both scaling factors
scale_up_x = 1.2
scale_up_y = 1.2
# Scaling Down the image 0.6 times specifying a single scale factor.
scale_down = 0.6
scaled_f_down = cv2.resize(image, None, fx= scale_down, fy= scale_down, interpolation= cv2.INTER_LINEAR)
scaled_f_up = cv2.resize(image, None, fx= scale_up_x, fy= scale_up_y, interpolation= cv2.INTER_LINEAR)
3.3.3 根据插值方式调整大小
- INTER_AREA: INTER_AREA uses pixel area relation for resampling. This is best suited for reducing the size of an image (shrinking). When used for zooming into the image, it uses the INTER_NEAREST method.
- INTER_CUBIC: This uses bicubic interpolation for resizing the image. While resizing and interpolating new pixels, this method acts on the 4×4 neighboring pixels of the image. It then takes the weights average of the 16 pixels to create the new interpolated pixel.
- INTER_LINEAR: This method is somewhat similar to the INTER_CUBIC interpolation. But unlike INTER_CUBIC, this uses 2×2 neighboring pixels to get the weighted average for the interpolated pixel.
- INTER_NEAREST: The INTER_NEAREST method uses the nearest neighbor concept for interpolation. This is one of the simplest methods, using only one neighboring pixel from the image for interpolation.
C++:
# Scaling Down the image 0.6 using different Interpolation Method
Mat res_inter_linear, res_inter_nearest, res_inter_area;
resize(image, res_inter_linear, Size(), scale_down, scale_down, INTER_LINEAR);
resize(image, res_inter_nearest, Size(), scale_down, scale_down, INTER_NEAREST);
resize(image, res_inter_area, Size(), scale_down, scale_down, INTER_AREA);
Python:
# Scaling Down the image 0.6 times using different Interpolation Method
res_inter_nearest = cv2.resize(image, None, fx= scale_down, fy= scale_down, interpolation= cv2.INTER_NEAREST)
res_inter_linear = cv2.resize(image, None, fx= scale_down, fy= scale_down, interpolation= cv2.INTER_LINEAR)
res_inter_area = cv2.resize(image, None, fx= scale_down, fy= scale_down, interpolation= cv2.INTER_AREA)
4. 总结
- resize() 将图像源数据，通过参数指定的画面尺寸，进行相应的插值调整。
其他API函数：
- imshow
- imwrite
- vconcat 数据源连接函数
5. 参考资料
【1】ubuntu22.04@laptop OpenCV Get Started