OpenCV chroma key

CMakeLists.txt

cmake_minimum_required( VERSION 3.0 )
project( so-opencv-calibration )

find_package( OpenCV 3.0.0 EXACT REQUIRED )
set( INPUT_FILENAME "${CMAKE_CURRENT_LIST_DIR}/input_00.png" ) # Input file, e.g. http://i.stack.imgur.com/WjER0.png

add_executable( mwe mwe.cpp )
target_compile_definitions( mwe PRIVATE -DINPUT_FILENAME="${INPUT_FILENAME}" )
target_include_directories( mwe PRIVATE ${OpenCV_INCLUDE_DIRS} )
target_link_libraries( mwe ${OpenCV_LIBS} )

input_00.png

mwe.cpp

#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>

#include <cassert>
#include <cmath>
#include <iostream>
#include <string>

namespace {
/**
 * @brief Convert BGR color to YCrCb color space.
 * @param bgr   Color (channel order BGR, range: [0, 255])
 *
 * Details can be found in the [documentation of OpenCV][1]
 *
 * [1]: http://docs.opencv.org/trunk/de/d25/imgproc_color_conversions.html
 */
cv::Scalar bgr2ycrcb( cv::Scalar bgr )
{
	double R = bgr[ 2 ];
	double G = bgr[ 1 ];
	double B = bgr[ 0 ];
	double delta = 128; // Note: change this value if image type isn't CV_8U.

	double Y  = 0.299 * R + 0.587 * G + 0.114 * B;
	double Cr = ( R - Y ) * 0.713 + delta;
	double Cb = ( B - Y ) * 0.564 + delta;

	return cv::Scalar( Y, Cr, Cb, 0 /* ignored */ );
}

/**
 * @brief Separate foreground from background using simple chroma keying.
 *
 * @param imageBGR   Image with monochrome background
 * @param chromaBGR  Color of the background (using channel order BGR and range [0, 255])
 * @param tInner     Inner threshold, color distances below this value will be counted as foreground
 * @param tOuter     Outer threshold, color distances above this value will be counted as background
 *
 * @return  Mask (0 - background, 255 - foreground, [1, 255] - partially fore- and background)
 *
 * Details can be found on [Wikipedia][1].
 *
 * [1]: https://en.wikipedia.org/wiki/Chroma_key#Programming
 */
cv::Mat1b chromaKey( const cv::Mat3b & imageBGR, cv::Scalar chromaBGR, double tInner, double tOuter )
{
	// Basic outline:
	//
	// 1. Convert the image to YCrCb.
	// 2. Measure Euclidean distances of color in YCrBr to chroma value.
	// 3. Categorize pixels:
	//   * color distances below inner threshold count as foreground; mask value = 0
	//   * color distances above outer threshold count as background; mask value = 255
	//   * color distances between inner and outer threshold a linearly interpolated; mask value = [0, 255]

	assert( tInner <= tOuter );

	// Convert to YCrCb.
	assert( ! imageBGR.empty() );
	cv::Size imageSize = imageBGR.size();
	cv::Mat3b imageYCrCb;
	cv::cvtColor( imageBGR, imageYCrCb, cv::COLOR_BGR2YCrCb );
	cv::Scalar chromaYCrCb = bgr2ycrcb( chromaBGR ); // Convert a single BGR value to YCrCb.

	// Build the mask.
	cv::Mat1b mask = cv::Mat1b::zeros( imageSize );
	const cv::Vec3d key( chromaYCrCb[ 0 ], chromaYCrCb[ 1 ], chromaYCrCb[ 2 ] );

	for ( int y = 0; y < imageSize.height; ++y )
	{
		for ( int x = 0; x < imageSize.width; ++x )
		{
			const cv::Vec3d color( imageYCrCb( y, x )[ 0 ], imageYCrCb( y, x )[ 1 ], imageYCrCb( y, x )[ 2 ] );
			double distance = cv::norm( key - color );

			if ( distance < tInner )
			{
				// Current pixel is fully part of the background.
				mask( y, x ) = 0;
			}
			else if ( distance > tOuter )
			{
				// Current pixel is fully part of the foreground.
				mask( y, x ) = 255;
			}
			else
			{
				// Current pixel is partially part both, fore- and background; interpolate linearly.
				// Compute the interpolation factor and clip its value to the range [0, 255].
				double d1 = distance - tInner;
				double d2 = tOuter   - tInner;
				uint8_t alpha = static_cast< uint8_t >( 255. * ( d1 / d2 ) );

				mask( y, x ) = alpha;
			}
		}
	}

	return mask;
}

cv::Mat3b replaceBackground( const cv::Mat3b & image, const cv::Mat1b & mask, cv::Scalar bgColor )
{
	cv::Size imageSize = image.size();
	const cv::Vec3b bgColorVec( bgColor[ 0 ], bgColor[ 1 ], bgColor[ 2 ] );
	cv::Mat3b newImage( image.size() );

	for ( int y = 0; y < imageSize.height; ++y )
	{
		for ( int x = 0; x < imageSize.width; ++x )
		{
			uint8_t maskValue = mask( y, x );

			if ( maskValue >= 255 )
			{
				newImage( y, x ) = image( y, x );
			}
			else if ( maskValue <= 0 )
			{
				newImage( y, x ) = bgColorVec;
			}
			else
			{
				double alpha = 1. / static_cast< double >( maskValue );
				newImage( y, x ) = alpha * image( y, x ) + ( 1. - alpha ) * bgColorVec;
			}
		}
	}

	return newImage;
}

} // namespace

int main()
{
	std::string inputFilename = INPUT_FILENAME;
	std::string maskFilename = "./mask.png";
	std::string newBackgroundFilename = "./newBackground.png";

	// Load the input image.
	cv::Mat3b input = cv::imread( inputFilename, cv::IMREAD_COLOR );

	if ( input.empty() )
	{
		std::cerr << "Input file <" << inputFilename << "> could not be loaded ... " << std::endl;

		return 1;
	}

	// Apply the chroma keying and save the output.
	cv::Scalar chroma( 0, 0, 0, 0 );
	double tInner = 100.;
	double tOuter = 170.;
	cv::Mat1b mask = chromaKey( input, chroma, tInner, tOuter );

	cv::Mat3b newBackground = replaceBackground( input, mask, cv::Scalar( 0, 255, 0, 0 ) );

	cv::imwrite( maskFilename, mask );
	cv::imwrite( newBackgroundFilename, newBackground );

	cv::namedWindow( "input" );
	cv::imshow( "input", input );
	cv::namedWindow( "mask" );
	cv::imshow( "mask", mask );
	cv::namedWindow( "new background" );
	cv::imshow( "new background", newBackground );
	cv::waitKey( 0 );

	return 0;
}

Hello Nils Plath,
Can you please guide me how can i use it with xcode and i am new to this CMake!
How can i configure?

Can you please guide me how can i use it with xcode and i am new to this CMake!
How can i configure?