How to do Simple Image Binarization?¶

Introduction

Sometimes, we need to transform color images to monochrome image. There is one way that it is very simple to help you to do. You can download source code and binary files. Even I refer to OpenCV book, but I think it is so easy. I decide to implement it by myself.

Equipment

Operation System: Microsoft Windows 7 Professional (64 bit)
Development Utility: Microsoft Visual Studio 2010

Usage

// The height of the image.
for ( int iY = 0; iY < imageA->DibInfo->bmiHeader.biHeight; iY++ )
{
    // The width of the image.
    for ( int iX = 0; iX < imageA->DibInfo->bmiHeader.biWidth; iX++ )
    {
        // The index of pixel, because we use the three depth bit to present one pixel of color,
        // Therefore, we have to multiple three.
        lIDXA = ( iX * 3 ) + ( iY * imageA->DibInfo->bmiHeader.biWidth * 3 );
        // To get the pixel depth of the blue channel,
        byteRGB_BA = imageA->DibArry[lIDXA+0];
        // To get the pixel depth of the green channel.
        byteRGB_GA = imageA->DibArry[lIDXA+1];
        // To get the pixel depth of the red channel.
        byteRGB_RA = imageA->DibArry[lIDXA+2];
        // To transform RGB to Y (gray scale).
        dobYUV_YA =  (0.299 * byteRGB_RA + 0.587 * byteRGB_GA + 0.114 * byteRGB_BA);
        // Set our thresholds, To decide which pixel become to white. 
        if ( dobYUV_YA > 60 && dobYUV_YA < 160 )
        {
            lIDXB = ( iX * 3 ) + ( iY * imageB->DibInfo->bmiHeader.biWidth * 3 );
            imageB->DibArry[lIDXB+0] = 255;
            imageB->DibArry[lIDXB+1] = 255;
            imageB->DibArry[lIDXB+2] = 255;
        }
        // Otherwise, those pixels will be black.
        else
        {
            lIDXB = ( iX * 3 ) + ( iY * imageB->DibInfo->bmiHeader.biWidth * 3 );
            imageB->DibArry[lIDXB+0] = 0;
            imageB->DibArry[lIDXB+1] = 0;
            imageB->DibArry[lIDXB+2] = 0;
        }
    } // for ( int iX = 0; iX < imageA->DibInfo->bmiHeader.biWidth; iX++ )
} // for ( int iY = 0; iY < imageA->DibInfo->bmiHeader.biHeight; iY++ )

Download source code and binary files: https://drive.google.com/file/d/0BzHb_OyLyVZlUlNnUDU5U0Q3ZDQ/view?usp=sharing

Exception

1. There is a notice, if your bit depth of bitmap file are not 24 bits, you should change your bitmap files to adapt this program, or you could rewrite this source code to fit your bitmap format.

2. You have to install Microsoft SDK v7.1, because I include windowscodes.lib.
   #pragma comment(lib, "windowscodecs.lib")

Reference

[1] Gary Bradski and Adrian Kaehler, “Learning OpenCV: Computer Vision with the OpenCV Library,” O’REILLY, September 2008, ISBN:978-0-596-51613-0

Acknowledge

Thank you (Microsoft Visual Studio 2010, Lenna Sjööblom) very much for this great development utility and beautiful photo.