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Gamma Correction

This tutorial demonstrates how to capture a 2D image with a configurable gamma correction.

First, we connect to the camera.

C++

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auto camera = zivid.connectCamera();

Python

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camera = app.connect_camera()

Then we get the gamma as command line argument from user.

C++

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const double gamma = readGamma(argc, argv);
std::cout << "Capturing with gamma correction: " << gamma << std::endl;

Python

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user_options = _options()
print(f"Capturing with gamma correction: {user_options.gamma}")

We then capture the image with no gamma correction (gamma = 1.0) and with given gamma correction (in this case, gamma = 0.6).

C++

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cv::Mat bgrOriginal = captureBGRImage(camera, 1.0);
cv::Mat bgrAdjusted = captureBGRImage(camera, gamma);

Python

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bgr_original = _capture_bgr_image(camera, 1.0)
bgr_adjusted = _capture_bgr_image(camera, user_options.gamma)

The complete implementation of the function to capture a color image is given below.

C++

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cv::Mat captureBGRImage(Zivid::Camera &camera, const double gamma)
{
    std::cout << "Configuring settings" << std::endl;
    const auto settings2D = Zivid::Settings2D{ Zivid::Settings2D::Acquisitions{ Zivid::Settings2D::Acquisition{} },
                                               Zivid::Settings2D::Processing::Color::Gamma{ gamma } };

    std::cout << "Capturing 2D frame" << std::endl;
    const auto frame2D = camera.capture(settings2D);
    const auto image = frame2D.imageRGBA();
    auto bgr = imageToBGR(image);

    return bgr;
}

Python

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def _capture_bgr_image(camera: zivid.Camera, gamma: float) -> np.ndarray:
    """Capture and extract 2D image, then convert from RGBA and return BGR.

    Args:
        camera: Zivid Camera handle
        gamma: Gamma correction value

    Returns:
        bgr: BGR image (HxWx3 ndarray)

    """
    print("Configuring Settings")
    settings_2d = zivid.Settings2D(
        acquisitions=[zivid.Settings2D.Acquisition()],
    )
    settings_2d.processing.color.gamma = gamma

    print("Capturing 2D frame")
    with camera.capture(settings_2d) as frame_2d:
        image = frame_2d.image_rgba()
        rgba = image.copy_data()
        bgr = cv2.cvtColor(rgba, cv2.COLOR_RGBA2BGR)
        return bgr

For comparing the images with and without gamma correction, a combined image is created.

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cv::Mat combineImages(const cv::Mat &imageOne, const cv::Mat &imageTwo)
{
    cv::Mat combinedImage;
    int height = imageOne.rows;
    int width = imageOne.cols;
    cv::hconcat(
        imageOne(cv::Range(0, height), cv::Range(0, width / 2)),
        imageTwo(cv::Range(0, height), cv::Range(width / 2, width)),
        combinedImage);

    return combinedImage;
}

Python

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def _combine_images(image_one: np.ndarray, image_two: np.ndarray) -> np.ndarray:
    """Column-wise concatenate each half of two images together as one.

    Args:
        image_one: Left side of concatenated image
        image_two: Right side of concatenated image

    Returns:
        combined_image: Combined halves of each image

    """
    width = (int)(image_one.shape[1] / 2)
    combined_image = np.hstack([image_one[:, :width], image_two[:, -width:]])

    return combined_image

The images can then be displayed as one image.

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void displayBGR(const cv::Mat &bgr, const std::string &bgrName)
{
    cv::namedWindow(bgrName, cv::WINDOW_NORMAL);
    cv::imshow(bgrName, bgr);
    std::cout << "Press any key to continue" << std::endl;
    cv::waitKey(0);
}

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def _display_bgr(image: np.ndarray, bgr_name: str) -> None:
    """Display BGR image using OpenCV.

    Args:
        image: BGR image to be displayed
        bgr_name: Name of the OpenCV window

    """
    cv2.imshow(bgr_name, image)
    print("Press any key to continue")
    cv2.waitKey(0)

The resulting combined image is shown below, with the original half on the left side and the gamma corrected half on the right side.

C++

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std::cout << "Displaying color image before and after gamma correction: " << gamma << std::endl;
cv::Mat combinedImage = combineImages(bgrOriginal, bgrAdjusted);
displayBGR(combinedImage, "Original on left, adjusted on right");

Python

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print(f"Displaying color image before and after gamma correction: {user_options.gamma}")
combined_image = _combine_images(bgr_original, bgr_adjusted)
_display_bgr(combined_image, "Original on left, adjusted on right")