Convert between OpenCV Mat and Leptonica Pix

Question

I need to convert between OpenCV Mat image and Leptonica Pix image formats in C++. This is being used for binarization of 8bit gray images.

Answer 1

To convert pix to Mat add these line in @loot code before calling pix8toMat.

Pix *8bitPix = pixConvert1To8(NULL, pixt, 255, 0);

Now send this 8bitPix to mat conversion. [it works for binary image]

Answer 2

I found found @ikarliga's answer worked for me because what I needed was to actually convert to the Mat format not necessarily use it with the Tesseract API which is what that OP was asking.

Here are both the functions I use. The pix8ToMat function is taken from the node-dv project

Pix *mat8ToPix(cv::Mat *mat8)
{
    Pix *pixd = pixCreate(mat8->size().width, mat8->size().height, 8);
    for(int y=0; y<mat8->rows; y++) {
        for(int x=0; x<mat8->cols; x++) {
            pixSetPixel(pixd, x, y, (l_uint32) mat8->at<uchar>(y,x));
        }
    }
    return pixd;
}

cv::Mat pix8ToMat(Pix *pix8)
{
    cv::Mat mat(cv::Size(pix8->w, pix8->h), CV_8UC1);
    uint32_t *line = pix8->data;
    for (uint32_t y = 0; y < pix8->h; ++y) {
        for (uint32_t x = 0; x < pix8->w; ++x) {
            mat.at<uchar>(y, x) = GET_DATA_BYTE(line, x);
        }
        line += pix8->wpl;
    }
    return mat;
}

Answer 3

I know that i'm about 4 years late and nobody cares, but this task has frustrated me a lot 'cause leptonica's documentation is just awful.
The problem with @loot's answer is that it does not work with colored images, so here is my (maybe crude) modification of his pix8ToMat:

cv::Mat pixToMat(Pix *pix) {
    int width = pixGetWidth(pix);
    int height = pixGetHeight(pix);
    int depth = pixGetDepth(pix);

    cv::Mat mat(cv::Size(width, height), depth == 1 ? CV_8UC1 : CV_8UC3);

    for (uint32_t y = 0; y < height; ++y) {
        for (uint32_t x = 0; x < width; ++x) {
            if (depth == 1) {
                l_uint32 val;
                pixGetPixel(pix, x, y, &val);
                mat.at<uchar>(cv::Point(x, y)) = static_cast<uchar>(255 * val);
            } else {
                l_int32 r, g, b;
                pixGetRGBPixel(pix, x, y, &r, &g, &b);

                cv::Vec3b color(b, g, r);
                mat.at<cv::Vec3b>(cv::Point(x, y)) = color;
            }
        }
    }

    return mat;
}