OpenCV4萌新之路——詳解圖像讀取函數 「imread」

OpenCV4萌新之路——詳解圖像讀取函數 「imread」

• 1、函數簡析
• 2、參數詳解
• 1.String& filename
• 2.flags = IMREAD_COLOR
• 3、測試代碼
• 1. 輸入圖像參數
• 2. 輸出圖像顯示
• 3. 圖像參數
• 4. 其餘測試
• 4、參考文獻

處理圖像第一步固然是要讀取一張圖像，OpenCV給出的方法也很簡單：

Mat cv::imread(const String& filename, int flags = IMREAD_COLOR);

1、函數簡析

頭文件 #include <opencv2/imgcodecs.hpp>

imread	返回類型	命名空間	函數名	參數1	參數2
詳細	Mat	cv	imread	const String& filename	int flags = IMREAD_COLOR
詳細	-	-	-	文件路徑+文件名	圖像讀取模式

2、參數詳解

1.String& filename

輸入可爲相對路徑也可爲絕對路徑，運用方法參見測試代碼。

注：
imread函數支持讀取的圖像格式有
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)

2.flags = IMREAD_COLOR

值	枚舉名	定義	解釋
-1	IMREAD_UNCHANGED	If set, return the loaded image as is (with alpha channel, otherwise it gets cropped). Ignore EXIF orientation.	若是設置，則按原樣返回加載的圖像（使用Alpha通道，不然會被裁剪）
0	IMREAD_GRAYSCALE	If set, always convert image to the single channel grayscale image (codec internal conversion).	若是設置，則始終將圖像轉換爲單通道灰度圖像（編解碼器內部轉換）
1	IMREAD_COLOR	If set, always convert image to the 3 channel BGR color image.	若是設置，請始終將圖像轉換爲3通道BGR彩色圖像
2	IMREAD_ANYDEPTH	If set, return 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit.	若是設置，則在輸入具備相應深度時返回16位/ 32位圖像，不然將其轉換爲8位
4	IMREAD_ANYCOLOR	If set, the image is read in any possible color format.	若是設置，則以任何可能的顏色格式讀取圖像
8	IMREAD_LOAD_GDAL	If set, use the gdal driver for loading the image.	若是設置，使用gdal驅動程序加載圖像
16	IMREAD_REDUCED_GRAYSCALE_2	If set, always convert image to the single channel grayscale image and the image size reduced 1/2.	若是設置，則始終將圖像轉換爲單通道灰度圖像，圖像尺寸減少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.	若是設置，則始終將圖像轉換爲3通道BGR彩色圖像，圖像尺寸減少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.	若是設置，則始終將圖像轉換爲單通道灰度圖像，圖像尺寸減少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.	若是設置，則始終將圖像轉換爲3通道BGR彩色圖像，圖像尺寸減少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.	若是設置，則始終將圖像轉換爲單通道灰度圖像，圖像尺寸減少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.	若是設置，則始終將圖像轉換爲3通道BGR彩色圖像，圖像尺寸減少1/8
128	IMREAD_IGNORE_ORIENTATION	If set, do not rotate the image according to EXIF’s orientation flag.	若是設置，請不要根據EXIF的方向標誌旋轉圖像

3、測試代碼

#include<iostream>
#include<opencv2/opencv.hpp>
using namespace cv;
using namespace std;

#define IMAGE_ABSOLUTE_PATH "F:/Leraning_OpenCV4/Sakai_Izumi.jpg" //絕對路徑
#define IMAGE_RELATIVE_PATH "./Sakai_Izumi.jpg" //相對路徑

int main()
{

	//讀取圖片
	Mat src = imread(IMAGE_ABSOLUTE_PATH, IMREAD_COLOR);
	//Mat src = imread(IMAGE_RELATIVE_PATH, 1);

	//判讀是否成功讀取圖片
	if (src.empty())
	{
		std::cout << "Load img failed!" << endl;
		return 0;
	}
	else
	{
		std::cout << "Load img success!" << endl;
	}

	//顯示圖片
	imshow("src", src);
	waitKey(0);

	return 1;
}

1. 輸入圖像參數

2. 輸出圖像顯示

3. 圖像參數

4. 其餘測試

ImreadModes 0 讀取灰度圖

ImreadModes 16 讀取灰度圖，寬、高都爲原圖的1/2

你們能夠參考IMREAD_COLOR中不一樣的圖像讀取模式，對比一下顯示圖像，體會一下差別在哪。

4、參考文獻

1. Image file reading and writing.