cv::cuda::resize not working properly with shared memory

asked 2020-11-12 16:21:21 -0500

warpstar22 gravatar image

updated 2020-11-12 18:15:15 -0500

I have a class called UnifiedMemoryMat which uses cudaMallocManaged to share memory between a cv::Mat and cv::cuda::GpuMat. These two are accessible from the class by the user with m_image_cpu and m_image_gpu. My application is capturing images and then processing them in the shared memory UnifiedMemoryMat. I use cv::cuda::resize with umm.m_image_gpu. When I proceed to my next capure, I am not able to upload the new image to my shared memory and the old image stays there. I verify that the image is uploaded properly with if( != m_um_ptr) where m_um_ptr is a void * that I send to cudaMallocaManaged(). This behavior is extra weird because it works properly when I use cv::resize with umm.m_image_cpu. Even weirder, I can get cv::cuda::resize to work properly if earlier in the program I have cv::GpuMat image_gpu = umm.m_image_gpu. This doesn't cause an upload issue in my UnifiedMemoryMat. The only difference between UnifiedMemoryMat umm and cv::GpuMat image_gpu is the scope they are declared in. umm is declared in an outer scope so that I don't have to reallocate the memory each while loop iteration. image_gpu is in the scope of each image capture, but they refer to the same image so I'm not sure why this issue would happen.

My UnifiedMemoryMat is defined as follows (this is simplified a bit): header:

class UnifiedMemoryMat {
    void *m_um_ptr;

        cv::Mat m_image_cpu;
        cv::cuda::GpuMat m_image_gpu;

        int allocateMemory(cv::Mat img);
        int uploadImage(cv::Mat img);


int UnifiedMemoryMat::allocateMemory(cv::Mat img) {
    unsigned int image_byte_size = img.rows * img.cols * img.channels();

    if(cudaMallocManaged(&um_ptr, image_byte_size) != cudaSuccess) {
        return -1;

    m_image_cpu = cv::Mat(img.size(), img.type(), m_um_ptr);
    m_image_gpu = cv::cuda::GpuMat(img.size(), img.type(), m_um_ptr);
   return 0;

int UnifiedMemoryMat::uploadImage(cv::Mat img) {
    if( != m_um_ptr) {
        return -1;
    return 0;

psuedocode of application:

UnifiedMemoryMat um_images[4];

//allocate memory for each um_images using UnifiedMemoryMat::allocateImage();

while(capturing) {
    cv::Mat images[4];
    cv::cuda::GpuMat images_gpu[4];

    //capture images

    for(int i = 0; i < 4; ++i) {
        um_images[i].uploadImage(camera_images); //problem occurs here after the first iteration when using cv::cuda::resize with um_images[i].m_image_gpu
        images[i] = um_images[i].m_image_cpu;
        image_gpu[i] = um_images[i].m_image_gpu;


    for(inti = 0; i < 4; ++i) {
        cv::resize(um_images[i].m_image_cpu, um_images[i].m_image_cpu, size); //works
        cv::resize(images[i], images[i], size); //works
        cv::cuda::resize(images_gpu[i], images_gpu[i], size); //works
        cv::cuda::reisze(um_images[i].m_image_gpu, um_images[i].m_image_gpu, size); //does not work
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Have you tried resizing with a new destination array? I have never tried using the same array, but I would assume that if the image is larger you would at least need a reallocation and the unified memory doesn't have a constructor to perform this.

How do you determine it doesn't work, what error codes do you get?

cudawarped gravatar imagecudawarped ( 2020-11-16 04:15:10 -0500 )edit

That's something I wasn't considering, but I can confirm that all the images are being resized down. I check if it's an error with if( != m_um_ptr) after uploading the image. The error happens for each image when I try to upload an image after the first time. The initial images will remain in shared memory.

warpstar22 gravatar imagewarpstar22 ( 2020-11-16 18:04:28 -0500 )edit != m_um_ptr implies a reallocation not an error in the resize. Are you 100% that cv::cuda::reisze(um_images[i].m_image_gpu, um_images[i].m_image_gpu, size); is not causing um_images[i].m_image_gpu to be reallocated because the destination is a different size to the source?

cudawarped gravatar imagecudawarped ( 2020-11-17 03:31:28 -0500 )edit

I see your point. I missed that being an issue because I was capturing the images in the same resolution in this case. If I change the capture size for one and try to resize, it throws an error when I'm trying to use hconcat before displaying. Thanks

warpstar22 gravatar imagewarpstar22 ( 2020-11-17 17:50:36 -0500 )edit