opencv - cvCaptureFromAvi:图像在x和y轴上翻转

Question

下面的代码将打开.avi文件。问题是:为什么图像在x和y轴上翻转，为什么？

#include <stdio.h>
#include <string.h>

#include <opencv/cv.h>
#include <opencv/highgui.h>
#include <opencv2/imgproc/imgproc.hpp>

#include <GLFW/glfw3.h>
#include <GL/glut.h>

#define VIEWPORT_WIDTH              1280
#define VIEWPORT_HEIGHT             800
#define KEY_ESCAPE                  27

CvCapture* capture;
GLFWwindow* window1;
GLFWwindow* window2;
IplImage *image;
static GLuint texName;

void initTexture(IplImage* Image);
void applyTexture(int img_width, int img_height);
void loadImage(IplImage*, GLFWwindow* window);

int main(int argc, char* argv[])
{

    if (!glfwInit())
        exit(EXIT_FAILURE);

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(1000,1000);

    int count;
    GLFWmonitor** monitors = glfwGetMonitors(&count);
    window1 = glfwCreateWindow(VIEWPORT_WIDTH, VIEWPORT_HEIGHT, "Simple example1", NULL, NULL);

    capture = cvCaptureFromAVI("foo.avi");
    assert(capture);

    // Initialize OpenGL
    glfwMakeContextCurrent(window1);

    while (!glfwWindowShouldClose(window1))
    {
        image = cvQueryFrame(capture);

        if(!cvGrabFrame(capture)){              // capture a frame 
            printf("Could not grab a frame\n\7");
            exit(0);
        }

        glfwMakeContextCurrent(window1);
        loadImage(image, window1);

    }

    return 0;
}

void initTexture(IplImage *Image)
{
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glShadeModel(GL_FLAT);
    glEnable(GL_DEPTH_TEST);

    glGenTextures(1, &texName);
    glBindTexture(GL_TEXTURE_2D, texName);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    glTexImage2D(GL_TEXTURE_2D, 0,  4 , Image->width, Image->height, 0, GL_BGR, GL_UNSIGNED_BYTE, Image->imageData);
}

void applyTexture(int img_width, int img_height)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_TEXTURE_2D);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
    glBindTexture(GL_TEXTURE_2D, texName);
    glBegin(GL_QUADS);
    glTexCoord2f(0, 0); glVertex3f(VIEWPORT_WIDTH /2, VIEWPORT_HEIGHT/2, 0);
    glTexCoord2f(0, 1); glVertex3f(VIEWPORT_WIDTH /2, VIEWPORT_HEIGHT/2+img_height, 0);
    glTexCoord2f(1, 1); glVertex3f(VIEWPORT_WIDTH /2+img_width, VIEWPORT_HEIGHT/2+img_height, 0);
    glTexCoord2f(1, 0); glVertex3f(VIEWPORT_WIDTH /2+img_width, VIEWPORT_HEIGHT/2, 0);
    glEnd();
    glFlush();
    glDisable(GL_TEXTURE_2D);
}

void loadImage(IplImage *Image, GLFWwindow* window)
{
    initTexture(Image);
    glViewport(0, 0, VIEWPORT_WIDTH , VIEWPORT_HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, VIEWPORT_WIDTH , 0, VIEWPORT_HEIGHT, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    applyTexture(Image->width,Image->height);
    glfwSwapBuffers(window);
    glfwPollEvents();
}

Answer 1

这是因为OpenCV假定图像的原点(0,0)位于顶部左上角。相反，OpenGL必须起源于底部左上角。您可以按以下方式修复代码:

glTexCoord2f(0, 1); glVertex3f(VIEWPORT_WIDTH /2, VIEWPORT_HEIGHT/2, 0);
glTexCoord2f(0, 0); glVertex3f(VIEWPORT_WIDTH /2, VIEWPORT_HEIGHT/2+img_height, 0);
glTexCoord2f(1, 0); glVertex3f(VIEWPORT_WIDTH /2+img_width, VIEWPORT_HEIGHT/2+img_height, 0);
glTexCoord2f(1, 1); glVertex3f(VIEWPORT_WIDTH /2+img_width, VIEWPORT_HEIGHT/2, 0);