[OpenCV] Custom Color Map

이번 포스팅에서는 사용자 정의 컬러맵(Custom Color Map)에 대하여 알아보기로 하겠습니다.

사용자 정의 컬러맵은 컬러의 변화를 B, G, R 채널에 대하여 각각 정의하고 이를 이용하여 LUT(Look Up Table)를 생성하는 것입니다.

1. B, G, R 채널에 대한 연속적 변화 정의

다음과 같이 B, G, R 채널 변화를 정의하였습니다.

unsigned char b[] = {

255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,253,251,249,247,245,242,241,238,237,235,233,231,229,227,225,223,221,219,217,215,213,211,209,207,205,203,201,199,197,195,193,191,189,187,185,183,181,179,177,175,173,171,169,167,165,163,161,159,157,155,153,151,149,147,145,143,141,138,136,134,132,131,129,126,125,122,121,118,116,115,113,111,109,107,105,102,100,98,97,94,93,91,89,87,84,83,81,79,77,75,73,70,68,66,64,63,61,59,57,54,52,51,49,47,44,42,40,39,37,34,33,31,29,27,25,22,20,18,17,14,13,11,9,6,4,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};

unsigned char g[] = { 255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,254,252,250,248,246,244,242,240,238,236,234,232,230,228,226,224,222,220,218,216,214,212,210,208,206,204,202,200,198,196,194,192,190,188,186,184,182,180,178,176,174,171,169,167,165,163,161,159,157,155,153,151,149,147,145,143,141,139,137,135,133,131,129,127,125,123,121,119,117,115,113,111,109,107,105,103,101,99,97,95,93,91,89,87,85,83,82,80,78,76,74,72,70,68,66,64,62,60,58,56,54,52,50,48,46,44,42,40,38,36,34,32,30,28,26,24,22,20,18,16,14,12,10,8,6,4,2,0 };

unsigned char r[] = {

195,194,193,191,190,189,188,187,186,185,184,183,182,181,179,178,177,176,175,174,173,172,171,170,169,167,166,165,164,163,162,161,160,159,158,157,155,154,153,152,151,150,149,148,147,146,145,143,142,141,140,139,138,137,136,135,134,133,131,130,129,128,127,126,125,125,125,125,125,125,125,125,125,125,125,125,125,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126};

2. Channel Matrix 정의

cv::Mat channels[] = { cv::Mat( 256, 1, CV_8U, b ), cv::Mat( 256, 1, CV_8U, g ), cv::Mat( 256, 1, CV_8U, r ) };

각 array element는 256 × 1의 일종의 벡터 형태의 행렬로 정의됩니다.

3. 3개의 Channel을 LUT로 합치기

cv::Mat lut; // Create a lookup table
cv::merge( channels, 3, lut );

cv::merge 함수의 Prototype은 다음과 같습니다:

void merge(const Mat* mv, size_t count, OutputArray dst);

4. 회색조로부터 컬러 LUT 생성

cv::Mat im_color;
cv::LUT( im_gray, lut, im_color );

cv::LUT 함수의 Prototype은 다음과 같습니다:

void LUT(InputArray src, InputArray lut, OutputArray dst);

Example Code

#include "opencv2/opencv.hpp"
 
using namespace std;
using namespace cv;
 
 
/*/////////////////////////////////////
@ function: applyCustomColorMap
    return: custom colormap
*//////////////////////////////////////
cv::Mat applyCustomColorMap( cv::Mat& im_gray )
{
    unsigned char b[] = {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,253,251,249,247,245,242,241,238,237,235,233,231,229,227,225,223,221,219,217,215,213,211,209,207,205,203,201,199,197,195,193,191,189,187,185,183,181,179,177,175,173,171,169,167,165,163,161,159,157,155,153,151,149,147,145,143,141,138,136,134,132,131,129,126,125,122,121,118,116,115,113,111,109,107,105,102,100,98,97,94,93,91,89,87,84,83,81,79,77,75,73,70,68,66,64,63,61,59,57,54,52,51,49,47,44,42,40,39,37,34,33,31,29,27,25,22,20,18,17,14,13,11,9,6,4,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
    unsigned char g[] = { 255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,254,252,250,248,246,244,242,240,238,236,234,232,230,228,226,224,222,220,218,216,214,212,210,208,206,204,202,200,198,196,194,192,190,188,186,184,182,180,178,176,174,171,169,167,165,163,161,159,157,155,153,151,149,147,145,143,141,139,137,135,133,131,129,127,125,123,121,119,117,115,113,111,109,107,105,103,101,99,97,95,93,91,89,87,85,83,82,80,78,76,74,72,70,68,66,64,62,60,58,56,54,52,50,48,46,44,42,40,38,36,34,32,30,28,26,24,22,20,18,16,14,12,10,8,6,4,2,0 };
    unsigned char r[] = {195,194,193,191,190,189,188,187,186,185,184,183,182,181,179,178,177,176,175,174,173,172,171,170,169,167,166,165,164,163,162,161,160,159,158,157,155,154,153,152,151,150,149,148,147,146,145,143,142,141,140,139,138,137,136,135,134,133,131,130,129,128,127,126,125,125,125,125,125,125,125,125,125,125,125,125,125,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,127,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126,126};
     
    cv::Mat channels[] = { cv::Mat( 256, 1, CV_8U, b ), cv::Mat( 256, 1, CV_8U, g ), cv::Mat( 256, 1, CV_8U, r ) };
    cv::Mat lut; // Create a lookup table
    cv::merge( channels, 3, lut );
     
    cv::Mat im_color;
    cv::LUT( im_gray, lut, im_color );
     
    return im_color;
 
}
 
 
/*/////////////////////////////////////
@ function: main
*//////////////////////////////////////
int main()
{
    /// Read 8-bit grayscale image
    cv::Mat im = imread( {YOUR_IMAGE_PATH}, IMREAD_GRAYSCALE );
    cv::cvtColor( im.clone(), im, COLOR_GRAY2BGR );
    cv::Mat im_color = applyCustomColorMap( im );
     
    cv::imshow( "Pseudo Colored Image", im_color );
    cv::waitKey( 0 );
}

Result

Source Image

Output Image