Unable to write images using imwrite in OpenCV

Question

I am trying to write to an image using imwrite as follows:

Mat object = imread ("C:/Users/User/Desktop/book.jpg", CV_LOAD_IMAGE_GRAYSCALE);
//calculate integral image
        Mat iObject;
        integral(object, iObject);
        imshow("Good Matches", iObject);
        imwrite("C:/Users/User/Desktop/IntegralImage.jpg", iObject);
        cvWaitKey(0);

but it does not suceed, I read about it, some solutions was to change jpg to bmp. I tried it also but no result! Any help please

Does it appear correctly when you do imshow? Are you using the account "User" and do you have access to write to "User"'s Desktop — RyanP, Oct 28 '15 at 17:21
yes imshow appear correctly.. How can I know if I have access to write? — user3552658, Oct 28 '15 at 17:22
What's the problem? You can't save the image, or the image is saved but it's basically all white? — Miki, Oct 28 '15 at 18:57
`bool ok = imwrite(...); if(!ok) {//error}`. Next time please use @name to notify. However, I can't reproduce your problem. Try starting Visual Studio or whatever IDE you're using as administrator, and retry. This will show if it's a permission problem — Miki, Oct 28 '15 at 23:13
@Miki it works Thanks :) Actually I has 2 images to save, One is saved successfully , The second is saved blank.. — user3552658, Oct 29 '15 at 06:36
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/93719/discussion-between-user3552658-and-miki). — user3552658, Oct 29 '15 at 18:30

score 1 · Accepted Answer · edited May 23 '17 at 11:58

Cannot save image

This is because you don't have the privileges to write in that location. Solutions:

Start your program as administrator
Change to a location where you have enough privileges

Integral image is saved blank

The integral image is of type CV_32UC1, so values higher than 255 will be saturated to 255, and saved as white. You can't recover original values from the saved image.

Solutions:

Normalize the values to fit the range [0,255], and save the CV_8U image. You can't recover original values from the saved image, but at least is scaled and shown correctly.
Use FileStorage to save the original data. You keep the original values.
If you need more speed that FileStorage, you can save raw binary data. See here for an example. You keep the original values.

This is a sample code to show solutions 1 and 2. For 3 please refer to the given link.

#include <opencv2\opencv.hpp>
using namespace cv;

int main()
{
    // Load image
    Mat1b object = imread("path_to_image", IMREAD_GRAYSCALE);

    // Calculate integral image
    Mat1i iObject;
    integral(object, iObject);

    imwrite("save_1i.png", iObject);

    // the saved image has saturated values

    // /////////////////////////////////////////

    // Save using imwrite
    Mat1b save_1b;
    normalize(iObject, save_1b, 255, 0, NORM_MINMAX);
    imwrite("save_1b.png", save_1b);

    // the saved image has scaled values, but displayed correctly


    // /////////////////////////////////////////

    // Save using FileStorage
    {
        FileStorage fs("save_fs.yml", FileStorage::WRITE);
        fs << "integral" << iObject;

        // the saved file has original values
    }


    // Load using FileStorage
    Mat1i loadedIObject;
    {
        FileStorage fs("save_fs.yml", FileStorage::READ);
        fs["integral"] >> loadedIObject;
    }

    // loadedIObject has original values

    return 0;
}

Unable to write images using imwrite in OpenCV

1 Answers1