Detect if image is color, grayscale or black and white with Python/PIL

Question

I extract pages images from a PDF file in jpeg format and I need to determine if each image is much more grayscale, color ou black and white (with a tolerance factor).

Answer 1

I personally prefer the answer of TomB. This is not a new answer, I just want to post the Java version:

private Mat calculateChannelDifference(Mat mat) {   

    // Create channel list:
    List channels = new ArrayList<>();

    for (int i = 0; i < 3; i++) {
        channels.add(new Mat());
    }

    // Split the channels of the input matrix:
    Core.split(mat, channels);

    Mat temp = new Mat();

    Mat result = Mat.zeros(mat.size(), CvType.CV_8UC1);

    for (int i = 0; i < channels.size(); i++) {

        // Calculate difference between 2 successive channels:
        Core.absdiff(channels.get(i), channels.get((i + 1) % channels.size()), temp);

        // Add the difference to the result:
        Core.add(temp, result, result);
    }

    return result;
}

The result is the difference as an matrix, this way you could apply some threshold and even detect shapes. If you want the result as a single number, you will just have to calculate the average value. This can be done using Core.mean()