OpenCv 006 --- the role of the LUT and usage

A used OpenCv API:

/** @brief Applies a GNU Octave/MATLAB equivalent colormap on a given image.

@param src The source image, grayscale or colored of type CV_8UC1 or CV_8UC3.
@param dst The result is the colormapped source image. Note: Mat::create is called on dst.
@param colormap The colormap to apply, see #ColormapTypes
*/

CV_EXPORTS_W void applyColorMap(InputArray src, OutputArray dst, int colormap);

 #ColormapTypes

COLORMAP_AUTUMN = 0, //!< 

COLORMAP_BONE = 1, //!< 

COLORMAP_JET = 2, //!< ![jet](pics/colormaps/colorscale_jet.jpg）

COLORMAP_WINTER = 3, //!< 

COLORMAP_RAINBOW = 4, //!< 

COLORMAP_OCEAN = 5, //!< 

COLORMAP_SUMMER = 6, //!< 

COLORMAP_SPRING = 7, //!< 

COLORMAP_COOL = 8, //!< 

COLORMAP_HSV = 9, //!< 

COLORMAP_PINK = 10, //!< 

COLORMAP_HOT = 11, //!< 

COLORMAP_PARULA = 12 //! <! [Parula] (pics / colormaps / colorscale_parula.jpg)

2 test code

#include "opencv2\opencv.hpp"
#include <iostream>

using namespace std;
using namespace cv;

void myColorMap(Mat &grayImg);

int main(int argc, char**argv)
{
    Mat src = imread("G:\\CVworkstudy\\program_wwx\\研习社140课时\\ZhaiZhigang140\\Blender_Suzanne1.jpg");
    if (src.empty())
    {
        printf("Could not load image...\n");
        return -1;
    }
    imshow("sourceImg", src);
    Mat grayLutDemo, dst;
    // 使用LUT
    applyColorMap(src, dst, COLORMAP_HSV);
    // 显示结果
    imshow("ColorMap", dst);

    cvtColor(src, grayLutDemo, COLOR_BGR2GRAY);
    myColorMap(grayLutDemo);
    imshow("GrayLutDemo", grayLutDemo);
    waitKey(0);
    return 0;
}

void myColorMap(Mat &grayImg)
{
    int lut[256 ];
     // this loop may be performed for other operations of the corresponding pixel value to a pixel value specified
     // here corresponds to the single-channel image pixel binarization processing is performed 
    for ( int I = 0 ; I < 256 ; I ++ ) {
         IF (I < 127 ) { 
            LUT [I] = 0 ; 
        } 
        the else 
            LUT [I] = 255 ; 
    } 

    int Hight = grayImg.rows;
     int width = grayImg.cols;
     for ( int Row = 0 ; row <hight; row ++) {
        for (int col = 0; col < width; col++) {
            uchar pv = grayImg.at<uchar>(row, col);
            grayImg.at<uchar>(row, col) = lut[pv];
        }
    }
}

3 code running results