Overlay canny edges on image in black - c++

Question

I have some simple code that performs canny edge detection and overlays the edges on the original image.
The code works, but I'd like the edges to be drawn in black, currently they're drawn in white.
static void sketchImage(Mat srcColor, Mat& dst, bool sketchMode, int debugType)
{
Mat srcGray;
Mat edgesBgr;
cvtColor(srcColor, srcGray, CV_BGRA2GRAY);
cvtColor(srcColor, srcColor, CV_BGRA2BGR);
GaussianBlur(srcGray, srcGray, cvSize(5, 5),1.2,1.2);
GaussianBlur(srcColor, srcColor, cvSize(5,5), 1.4, 1.4);
CvSize size = srcColor.size();
Mat edges = Mat(size, CV_8U);
Canny(srcGray, edges, 150, 150);
cvtColor(edges, edgesBgr, cv::COLOR_GRAY2BGR);
dst = srcColor + edgesBgr;
}
I'm sure this is pretty simple but I'm fairly new to openCV and I'd appreciate any help.
Full code as requested:
#import "ViewController.h"
#import "opencv2/highgui.hpp"
#import "opencv2/core.hpp"
#import "opencv2/opencv.hpp"
#import "opencv2/imgproc.hpp"
#interface ViewController ()
#property (weak, nonatomic) IBOutlet UIImageView *display;
#property (strong, nonatomic) UIImage* image;
#property (strong, nonatomic) UIImage* backup;
#property NSInteger clickflag;
#end
#implementation ViewController
using namespace cv;
- (IBAction)convert_click:(id)sender {
NSLog(#"Clicked");
if (_clickflag == 0)
{
cv::Mat cvImage, cvBWImage;
UIImageToMat(_image, cvImage);
//cv::cvtColor(cvImage, cvBWImage, CV_BGR2GRAY);
//cvBWImage = cvImage;
cartoonifyImage(cvImage, cvBWImage, false, 0);
_image = MatToUIImage(cvBWImage);
[_display setImage:_image];
_clickflag = 1;
}
else if(_clickflag == 1)
{
_image = _backup;
[_display setImage:_image];
_clickflag = 0;
}
}
static UIImage* MatToUIImage(const cv::Mat& m)
{
//CV_Assert(m.depth() == CV_8U);
NSData *data = [NSData dataWithBytes:m.data length:m.step*m.rows];
CGColorSpaceRef colorSpace = m.channels() == 1 ?
CGColorSpaceCreateDeviceGray() : CGColorSpaceCreateDeviceRGB();
CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
// Creating CGImage from cv::Mat
CGImageRef imageRef = CGImageCreate(m.cols, m.rows, m.elemSize1()*8, m.elemSize()*8,
m.step[0], colorSpace, kCGImageAlphaNoneSkipLast|kCGBitmapByteOrderDefault,
provider, NULL, false, kCGRenderingIntentDefault);
UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpace);
return finalImage;
}
static void UIImageToMat(const UIImage* image, cv::Mat& m)
{
CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
CGFloat cols = image.size.width;
CGFloat rows = image.size.height;
m.create(rows, cols, CV_8UC4); // 8 bits per component, 4 channels
CGContextRef contextRef = CGBitmapContextCreate(m.data, m.cols, m.rows, 8,
m.step[0], colorSpace, kCGImageAlphaNoneSkipLast | kCGBitmapByteOrderDefault);
CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
CGContextRelease(contextRef);
}
static void sketchImage(Mat srcColor, Mat& dst, bool sketchMode, int debugType)
{
Mat srcGray;
Mat edgesBgr;
cvtColor(srcColor, srcGray, CV_BGRA2GRAY);
cvtColor(srcColor, srcColor, CV_BGRA2BGR);
GaussianBlur(srcGray, srcGray, cvSize(5, 5),1.2,1.2);
GaussianBlur(srcColor, srcColor, cvSize(5,5), 1.4, 1.4);
CvSize size = srcColor.size();
Mat edges = Mat(size, CV_8U);
Canny(srcGray, edges, 150, 150);
cvtColor(edges, edgesBgr, cv::COLOR_GRAY2BGR);
//edgesBgr = edgesBgr.inv();
NSLog(#"%d, %d\n", srcColor.size().height, srcColor.size().width);
NSLog(#"%d, %d\n", edgesBgr.size().height, edgesBgr.size().width);
dst = edgesBgr + srcColor;
}
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
_image = [UIImage imageNamed:#"Robben.jpg"];
_backup = [UIImage imageNamed:#"Robben.jpg"];
_clickflag = 0;
[_display setImage:_image];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#end

Answer 1

static void sketchImage(Mat srcColor, Mat& dst, bool sketchMode, int debugType)
{
Mat srcGray;
cvtColor(srcColor, srcGray, CV_BGRA2GRAY);
cvtColor(srcColor, srcColor, CV_BGRA2BGR);
GaussianBlur(srcGray, srcGray, cvSize(5, 5),1.2,1.2);
GaussianBlur(srcColor, srcColor, cvSize(5,5), 1.4, 1.4);
CvSize size = srcColor.size();
Mat edges = Mat(size, CV_8U);
Canny(srcGray, edges, 150, 150);
dst = srcColor.clone();
dst.setTo(0,edges);
}

Answer 2

You could apply bitwise_not(dst,dst) so that white becomes black and black becomes white !
void bitwise_not(InputArray src, OutputArray dst, InputArray
mask=noArray())