CODEWITHSUNDEEP
c++image-processingcimg
ckjbgames
ckjbgames

Reputation: 123

How to test if a pixel in an image is of a certain color in CImg?

I am writing a program with CImg where I want to test if a pixel in an image is the color #00FF00. How do I do this?

Upvotes: 2

Views: 1889

Answers (2)

Mark Setchell
Mark Setchell

Reputation: 207873

To test pixel at column c, row r is green:

if((img(c,r,0,0)==0) &&
   (img(c,r,0,1)==255) &&
   (img(c,r,0,2)==0)) ...

Here is a 5x1 pixel image, with red, green, blue, white and black pixels in a single row that you can test with. Save it as image.ppm.

P3
5 1
255
255 0 0 0 255 0 0 0 255 255 255 255 0 0 0

Enlarged appearance:

enter image description here

Here is a full example:

////////////////////////////////////////////////////////////////////////////////
// main.cpp
//
// CImg example of accessing pixels
//
// Build with: g++-6 -std=c++11  main.cpp -o main
// or:         clang++ main.cpp -o main
////////////////////////////////////////////////////////////////////////////////
#include <iostream>
#include <cstdlib>

#define cimg_display 0
#include "CImg.h"

using namespace cimg_library;
using namespace std;

int main() {
    // Load image
    CImg<unsigned char> img("image.ppm");

    // Get width, height, number of channels
    int w=img.width();
    int h=img.height();
    int n=img.spectrum();
    cout << "Dimensions: " << w << "x" << h << " " << n << " channels" <<endl;

    // Dump all pixels
    for(int r=0;r<h;r++){
       for(int c=0;c<w;c++){
          char hex[16];
          sprintf(hex,"#%02x%02x%02x",img(c,r,0),img(c,r,1),img(c,r,2));
          cout << r << "," << c << " " << hex << endl;
          if((img(c,r,0,0)==0) &&
             (img(c,r,0,1)==255) &&
             (img(c,r,0,2)==0)){
             cout << "This pixel is green" << endl;
          }
       }
    }
}

Sample Output

The program produces this when run with the sample ppm file above:

Dimensions: 5x1 3 channels
0,0 #ff0000
0,1 #00ff00
This pixel is green
0,2 #0000ff
0,3 #ffffff
0,4 #000000

Upvotes: 2

Omar Martinez
Omar Martinez

Reputation: 708

You can get a COLORREF by calling CImage::GetPixel(int xPos, int yPos);

With the COLORREF you can than create a new COLORREF and compare the two:

CImage image;
COLORREF pixelColor = image.getPixel(451, 524); // this gets the color at (451,524) as a COLORREF
COLORREF greenColor = RGB(0, 255, 0);
if(pixelColor == greenColor)
{
    // THE COLORS ARE THE SAME!
}

Upvotes: -1

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