【图像处理】resize c++实现

opencv resize c++实现

主要用到插值。
首先是对列方向插值，然后对行方向插值。参考了yolov3中resize图片源码

#include <iostream>
#include <stdlib.h>
#include <opencv2/opencv.hpp>

unsigned char getval(unsigned char* ptr, int cols, int height, int width)
{
	return ptr[height*cols + width];
}

void setval(unsigned char* ptr, int cols, int height, int width, unsigned char pixel)
{
	ptr[height*cols + width] = pixel;
}

unsigned char* resize(unsigned char* ptr, int rows, int cols, int h, int w)
{
	unsigned char* part = (unsigned char*)malloc(sizeof(unsigned char)*w*rows);
	unsigned char* dst = (unsigned char*)malloc(sizeof(unsigned char)*w*h);

	float wscale = cols / (float)w;
	float hscale = rows / (float)h;

	unsigned char val;
	for (int r = 0; r < rows; r++)
		for (int c = 0; c < w; c++)
		{
			if (c == 0 || c == w - 1)
			{
				val = getval(ptr, cols, r, c);
			}
			else
			{
				float x1 = c * wscale;
				int x2 = (int)x1;
				float diffx = x1 - x2;

				val = (1 - diffx)*getval(ptr, cols, r, x2) + diffx*getval(ptr, cols, r, x2 + 1);
			}
			setval(part, w, r, c, val);
		}

		for (int r = 0; r < h; r++)
		{
			float y1 = r * hscale;
			int y2 = (int)y1;
			float diffy = y1 - y2;
			for (int c = 0; c < w; c++)
			{
				if (r == 0 || r == h - 1)
				{
					val = getval(part, w, r, c);
				}
				else
				{
					val = (1 - diffy)*getval(part, w, y2, c) + diffy * getval(part, w, y2+1, c);
				}
				setval(dst, w, r, c, val);
			}
		}
	free(part);
	return dst;
}

int main(void)
{
	cv::Mat src = cv::imread("apple.jpg");
	cv::imshow("apple.jpg", src);
	cv::cvtColor(src, src, CV_BGR2GRAY);
	double t1 = cv::getTickCount();
	unsigned char* resizebf = resize(src.data, src.rows, src.cols, 416, 416);
	double t2 = cv::getTickCount() - t1;
	printf("resize cost time: %.3fms\n", t2 * 1000 / cv::getTickFrequency());

	cv::Mat dst;
	t1 = cv::getTickCount();
	cv::resize(src, dst, cv::Size(416, 416));
	t2 = cv::getTickCount() - t1;
	printf("opencv resize cost time: %.3fms\n", t2 * 1000 / cv::getTickFrequency());
	cv::Mat save(416, 416, CV_8UC1, resizebf);
	cv::imshow("test.jpg", save);
	cv::waitKey(0);
	free(resizebf);
	return 0;
}

对比两个resize的时间，上位机打印结果