在OPENGL中計算直方圖

Question

我嘗試使用OPENGL計算圖像的直方圖。 我已經閱讀了一些關於此的文章，但仍然出現錯誤。 我的直方圖緩沖區始終返回零。 我讀過的一些文章：

馬克諾爾直方圖

GPU-Android OpenGL ES 3.0中的亮度直方圖計算

我的代碼：

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <vector>

// Include GLEW
#include <GL/glew.h>

// Include GLFW
#include <GLFW/glfw3.h>
GLFWwindow* window;

// Include GLM
#include <glm/glm.hpp>
using namespace glm;
#include <SOIL.h>

// Shader sources
const GLchar* vertexSource = "\n"
"#version 330 core\n"
"attribute vec3 inPosition;\n"
"void main()\n"
"{\n"
"    float x = inPosition.x;\n"
"\n"
"    gl_Position = vec4(\n"
"        -1.0 + ((x) * 0.0078125),\n"
"        -1,\n"
"        0.0,\n"
"        1.0\n"
"    );\n"
"}\n";

const GLchar* fragmentSource = "\n"
"#version 330 core\n"
"out vec4 outputColor;\n"
"void main()\n"
"{\n"
"    outputColor = vec4(1.0, 1.0, 1.0, 1.0);\n"
"}\n";

void CheckStatus(GLuint obj)
{
    GLint status = GL_FALSE, len = 10;
    if( glIsShader(obj) )   glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
    if( glIsProgram(obj) )  glGetProgramiv( obj, GL_LINK_STATUS, &status );
    if( status == GL_TRUE ) return;
    if( glIsShader(obj) )   glGetShaderiv( obj, GL_INFO_LOG_LENGTH, &len );
    if( glIsProgram(obj) )  glGetProgramiv( obj, GL_INFO_LOG_LENGTH, &len );
    std::vector< char > log( len, 'X' );
    if( glIsShader(obj) )   glGetShaderInfoLog( obj, len, NULL, &log[0] );
    if( glIsProgram(obj) )  glGetProgramInfoLog( obj, len, NULL, &log[0] );
    std::cerr << &log[0] << std::endl;
    exit( -1 );
}

GLfloat buffer[256];
GLuint hist[256];
float _image[512*512*3];

int main()
{
    // Initialise GLFW
    if( !glfwInit() )
    {
        fprintf( stderr, "Failed to initialize GLFW\n" );
        getchar();
        return -1;
    }

    glfwWindowHint(GLFW_SAMPLES, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    int width, height;
    unsigned char* image = SOIL_load_image("sample_gray.bmp", &width, &height, 0, SOIL_LOAD_RGB);
    unsigned char image_gray[width * height];
    printf("%d\t%d\n", width, height);

    for (int i = 0; i < width * height; ++i)
    {
        image_gray[i] = image[i * 3];
        _image[i * 3] = image[i * 3];
        _image[i * 3 + 1] = image[i * 3 + 1];
        _image[i * 3 + 2] = image[i * 3 + 2];
    }

    for (int i = 0; i < width * height; ++i)
    {
        hist[image_gray[i]]++;
    }

    // Open a window and create its OpenGL context
    window = glfwCreateWindow(width, height, "Basic", NULL, NULL);
    if( window == NULL ){
        fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
        getchar();
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

    // Initialize GLEW
    glewExperimental = true; // Needed for core profile
    if (glewInit() != GLEW_OK) {
        fprintf(stderr, "Failed to initialize GLEW\n");
        getchar();
        glfwTerminate();
        return -1;
    }

    // Ensure we can capture the escape key being pressed below
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);

    // Dark blue background
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);

    GLuint num_input_data = width * height;

    /* Upload data */
    glBufferData(GL_ARRAY_BUFFER, num_input_data * sizeof(float) * 3, _image, GL_STATIC_DRAW);

    GLuint vertexShader, fragmentShader, shaderProgram;
    // Create and compile the vertex shader
    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexSource, NULL);
    glCompileShader(vertexShader);
    CheckStatus(vertexShader);
    // Create and compile the fragment shader
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSource, NULL);
    glCompileShader(fragmentShader);
    CheckStatus(fragmentShader);
    // Link the vertex and fragment shader into a shader program
    shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glBindFragDataLocation(shaderProgram, 0, "outputColor");
    glLinkProgram(shaderProgram);


    CheckStatus(shaderProgram);

    glUseProgram(shaderProgram);


    // Specify the layout of the vertex data
    GLint posAttrib = glGetAttribLocation(shaderProgram, "inPosition");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), 0);

    GLuint tex;
    GLuint fbo;
    glGenTextures(1, &tex);
    glBindFramebuffer(GL_FRAMEBUFFER, fbo);

    glGenFramebuffers(1, &fbo);
    glActiveTexture(GL_TEXTURE0);
    // glBindTexture(GL_TEXTURE_2D, tex);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexStorage2D(GL_TEXTURE_2D, 1, GL_R32F, 256, 1);
    // glBindTexture(GL_TEXTURE_2D, 0);

    glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, tex, 0);

    /* Clear buffer */
    glClearColor(1.0, 0.0, 0.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glBlendEquation(GL_FUNC_ADD);
    glBlendFunc(GL_ONE, GL_ONE);
    glEnable(GL_BLEND);

    /* Init viewport */
    glViewport(0, 0, 256, 1);
    glUseProgram(shaderProgram);
    /* Draw */
    glDrawArrays(GL_POINTS, 0, num_input_data);


    glReadPixels(0, 0, 256, 1, GL_RED, GL_FLOAT, buffer);

    for (int i = 0; i < 256; ++i)
    {
        printf("%d\t%f\t%d\n", i, buffer[i], hist[i]);
    }

}

有人可以幫助我嗎，謝謝。

我已經更新了我的代碼，現在可以使用了：D

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <vector>
// Include GLEW
#include <GL/glew.h>

// Include GLFW
#include <GLFW/glfw3.h>
GLFWwindow* window;

// Include GLM
#include <glm/glm.hpp>
using namespace glm;
#include <SOIL.h>

// Shader sources
const GLchar* vertexSource = "\n"
"#version 330 core\n"
"in vec3 inPosition;\n"
"void main()\n"
"{\n"
"    float x = inPosition.x;\n"
"\n"
"    gl_Position = vec4(\n"
"        -1.0 + ((x + 1) * 0.0078125),\n"
"        0.0,\n"
"        0.0,\n"
"        1.0\n"
"    );\n"
"}\n";

const GLchar* fragmentSource = "\n"
"#version 330 core\n"
"out vec4 outputColor;\n"
"void main()\n"
"{\n"
"    outputColor = vec4(1.0, 1.0, 1.0, 1.0);\n"
"}\n";

void CheckStatus(GLuint obj)
{
    GLint status = GL_FALSE, len = 10;
    if( glIsShader(obj) )   glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
    if( glIsProgram(obj) )  glGetProgramiv( obj, GL_LINK_STATUS, &status );
    if( status == GL_TRUE ) return;
    if( glIsShader(obj) )   glGetShaderiv( obj, GL_INFO_LOG_LENGTH, &len );
    if( glIsProgram(obj) )  glGetProgramiv( obj, GL_INFO_LOG_LENGTH, &len );
    std::vector< char > log( len, 'X' );
    if( glIsShader(obj) )   glGetShaderInfoLog( obj, len, NULL, &log[0] );
    if( glIsProgram(obj) )  glGetProgramInfoLog( obj, len, NULL, &log[0] );
    std::cerr << &log[0] << std::endl;
    exit( -1 );
}

void _check_gl_error(int line) 
{
    GLenum err (glGetError());

    while(err!=GL_NO_ERROR) 
    {
        std::string error;

        switch(err) 
        {
            case GL_INVALID_OPERATION:      error="INVALID_OPERATION";      break;
            case GL_INVALID_ENUM:           error="INVALID_ENUM";           break;
            case GL_INVALID_VALUE:          error="INVALID_VALUE";          break;
            case GL_OUT_OF_MEMORY:          error="OUT_OF_MEMORY";          break;
            case GL_INVALID_FRAMEBUFFER_OPERATION:  error="INVALID_FRAMEBUFFER_OPERATION";  break;
        }

        std::cerr << "GL_" << error.c_str() <<":"<<line<<std::endl;
        err=glGetError();
    }
}

GLfloat buffer[256];
GLuint hist[256];
float _image[512*512*3];

int main()
{
    // Initialise GLFW
    if( !glfwInit() )
    {
        fprintf( stderr, "Failed to initialize GLFW\n" );
        getchar();
        return -1;
    }

    glfwWindowHint(GLFW_SAMPLES, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    int width, height;
    unsigned char* image = SOIL_load_image("sample_gray.bmp", &width, &height, 0, SOIL_LOAD_RGB);
    unsigned char* image_gray = new unsigned char[width * height];

    printf("%d\t%d\n", width, height);


    for (int i = 0; i < width * height; ++i)
    {
        image_gray[i] = image[i * 3];
        _image[i * 3] = image[i * 3];
        _image[i * 3 + 1] = image[i * 3 + 1];
        _image[i * 3 + 2] = image[i * 3 + 2];
    }

    for (int i = 0; i < width * height; ++i)
    {
        hist[image_gray[i]]++;
    }

    // Open a window and create its OpenGL context
    window = glfwCreateWindow(width, height, "Basic", NULL, NULL);
    if( window == NULL ){
        fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
        getchar();
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

    // Initialize GLEW
    glewExperimental = true; // Needed for core profile
    if (glewInit() != GLEW_OK) {
        fprintf(stderr, "Failed to initialize GLEW\n");
        getchar();
        glfwTerminate();
        return -1;
    }
    _check_gl_error(__LINE__);
    // Ensure we can capture the escape key being pressed below
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);

    // Dark blue background
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);


    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);

    GLuint num_input_data = width * height;

    /* Upload data */
    glBufferData(GL_ARRAY_BUFFER, num_input_data * sizeof(float) * 3, _image, GL_STATIC_DRAW);

    GLuint vertexShader, fragmentShader, shaderProgram;
    // Create and compile the vertex shader
    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexSource, NULL);
    glCompileShader(vertexShader);
    CheckStatus(vertexShader);
    // Create and compile the fragment shader
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSource, NULL);
    glCompileShader(fragmentShader);
    CheckStatus(fragmentShader);
    // Link the vertex and fragment shader into a shader program
    shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glBindFragDataLocation(shaderProgram, 0, "outputColor");
    glLinkProgram(shaderProgram);


    CheckStatus(shaderProgram);

    glUseProgram(shaderProgram);


    // Specify the layout of the vertex data
    GLint posAttrib = glGetAttribLocation(shaderProgram, "inPosition");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), 0);

    GLuint tex;
    GLuint fbo;
    glGenFramebuffers(1, &fbo);
    glBindFramebuffer(GL_FRAMEBUFFER, fbo);

    glGenTextures(1, &tex);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_R32F, 256, 1, 0, GL_RED, GL_FLOAT, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    // glTexStorage2D(GL_TEXTURE_2D, 1, GL_R32F, 256, 1);

    glBindTexture(GL_TEXTURE_2D, 0);

    glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, tex, 0);

    glBindFramebuffer(GL_FRAMEBUFFER, 0);

    _check_gl_error(__LINE__);

    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
    /* Clear buffer */
    glClearColor(0.0, 0.0, 0.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glBlendEquation(GL_FUNC_ADD);
    glBlendFunc(GL_ONE, GL_ONE);
    glEnable(GL_BLEND);
    _check_gl_error(__LINE__);


    /* Init viewport */
    glViewport(0, 0, 256, 1);
    glUseProgram(shaderProgram);
    /* Draw */
    glDrawArrays(GL_POINTS, 0, num_input_data);


    glReadPixels(0, 0, 256, 1, GL_RED, GL_FLOAT, buffer);
    _check_gl_error(__LINE__);
    for (int i = 0; i < 256; ++i)
    {
        printf("%d\t%f\t%d\n", i, buffer[i], hist[i]);
    }
    free(image_gray);
}

特別感謝@Vallentin的熱情！

Answer 1

我的直方圖緩沖區始終返回零。

有趣。 因為我不知道哪個編譯器像這樣運行：

int width, height;
unsigned char* image = SOIL_load_image("sample_gray.bmp", &width, &height, 0, SOIL_LOAD_RGB);
unsigned char image_gray[width * height];

您需要執行的操作：

unsigned char *image_gray = new unsigned char[width * height];

請記住，稍后釋放內存delete[] image_gray 。

您的着色器也無法編譯，或者您的驅動程序比我的更精簡。 給出#version 330 core ，你不能使用attribute和將要使用in 。

in vec3 inPosition;

就像CheckStatus()告訴我們：

0(3) : error C7555: 'attribute' is deprecated, use 'in/out' instead

您還試圖綁定一個甚至還沒有的幀緩沖區。

GLuint fbo;
glBindFramebuffer(GL_FRAMEBUFFER, fbo);
[...]
glGenFramebuffers(1, &fbo);

您需要翻轉一下：

GLuint fbo;
glGenFramebuffers(1, &fbo);
glBindFramebuffer(GL_FRAMEBUFFER, fbo);

這也讓我感到困惑，為什么當MSVC向我尖叫時，您的編譯器為何會讓幻燈片下滑。

Error C4700 uninitialized local variable 'fbo'

在對紋理進行任何更改之前，您也不會綁定紋理。

// glBindTexture(GL_TEXTURE_2D, tex);

取消注釋glBindTexture() 。

您也沒有創建任何頂點數組。 哪種檢查glGetError()會告訴您。

GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);

在調用glEnableVertexAttribArray()之前執行此操作。

另外，您的透明顏色是紅色。 因此，這對您沒有太大幫助。 現在，您對glReadPixels()調用只會產生1.0 。

glClearColor(0.0, 0.0, 0.0, 1.0)

現在glReadPixels()仍然只產生零。 但是，取消綁定或根本不創建幀緩沖區。 然后，它給出了我認為是理想的結果。 由於不應該使用幀緩沖區，所以我懷疑它有問題。 但是，我似乎無法通過瀏覽您的代碼來指出它。 但是，由於代碼中已經充滿了問題，因此這是一個公平的起點。

額外：

• 您的目標是OpenGL 3.3，而glTexStorage2D()是4.2的核心。 重要的是，如果您要確保支持glTexStorage2D() ，請使用目標4.2。
• 對glActiveTexture()的調用是多余的。
• 由於紋理的高度為1，請考慮使用1D紋理。
• 記住要檢查glGetError()或更好地利用調試輸出

---

編輯

首先，在創建窗口（和上下文）並調用_check_gl_error()之前，您不能調用glewInit() 。

可以使用__LINE__代替手動添加行號。 因此_check_gl_error(__LINE__) 。

再次不要使用紅色透明色。 使用黑色透明色glClearColor(0.0, 0.0, 0.0, 1.0) 。 混合1.0和說0.1導致1.1 ，它被鉗制回1.0 。 因此紅色通道從一開始就應該是0.0 。

我意識到了問題。 在頂點着色器中，您將y手動設置為-1.0 。 假設您正在繪制GL_POINTS ，這最終會掉出屏幕。 將其y設置為-0.9999似乎現在可以得到所需的結果。 但是，依靠它就像在玩火。

如果現在運行該應用程序，則將看到0.0和1.0的混合。 獲得1.0的原因是因為在片段着色器中，您將紅色通道的outputColor設置為1.0 。 再次總結所有這些可能是一個瘋狂的價值，但最終它將限制在1.0 。

而是嘗試：

outputColor = vec4(0.005, 1.0, 1.0, 1.0);

現在，您應該看到輸出增加和減少，而不是0.0或1.0 。 但是請注意，如果hist[i]大於200，那么任何值都將產生1.0 。 因為1 / 0.005 = 200 。

至少現在一切正常 。