iOS 12 + Mac OS X Mojave EXC_BAD_ACCESS on cvtColor

asked 2018-10-04 11:58:21 -0500

kingst gravatar image

updated 2018-10-04 12:13:47 -0500

I've been trying to integrate OpenCV into my iOS project, but have been having trouble with a null pointer exception. I installed version 3.4.2 using Cocoapods, and the following code snippet works fine:

#import <opencv2/opencv.hpp>
#import <opencv2/imgproc/imgproc.hpp>
#import <opencv2/imgcodecs/ios.h>

#import "OpenCVWrapper.h"

@implementation OpenCVWrapper

+ (UIImage *) process:(UIImage *) image {
    cv::Mat m;
    UIImageToMat(image, m);

    // this works fine

    return MatToUIImage(m);
}

But when I try to do a simple color conversion (or any type of manipulation for that matter) I get an EXC_BAD_ACCESS and it crashes my app

#import <opencv2/opencv.hpp>
#import <opencv2/imgproc/imgproc.hpp>
#import <opencv2/imgcodecs/ios.h>

#import "OpenCVWrapper.h"

@implementation OpenCVWrapper

+ (UIImage *) process:(UIImage *) image {
    cv::Mat m;
    UIImageToMat(image, m);

    cv::Mat gray;
    cv::cvtColor(m, gray, cv::COLOR_BGR2GRAY); // crashes here

    return MatToUIImage(gray);
}

I tried version 2 of opencv and tried stepping through the assembly, but wasn't able to figure out what was causing the problem.

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Comments

Have you maybe tried initializing gray? Try filling it first with zeros then do the color conversion. I had a weird issue like this as well awhile back with iOS. cv::Mat gray = cv::Mat::zeros(m.size(), CV_8UC1) And also be aware that UIImage is of RGBA whilst OpenCV operates on BGRA.

eshirima gravatar imageeshirima ( 2018-10-04 17:11:08 -0500 )edit

Thank you for the suggestion. I tried it out but still got the same error.

When you convert a UIImage to a cv::Mat will it be in the BGRA format? I had assumed that during the conversion that opencv would change the format to it's native form.

kingst gravatar imagekingst ( 2018-10-04 18:46:53 -0500 )edit

Can you please post the full error log?

eshirima gravatar imageeshirima ( 2018-10-05 11:20:16 -0500 )edit