效果

原理

得到灰度化值，将灰度化的值带入0-255内，增加，得到可视化图形

源码

// 绘制直方图
QImage drawHistogram(const QImage &image)
{
    QVector<int> histogram(256, 0);

    // 计算图像的灰度直方图
    for (int y = 0; y < image.height(); ++y) {
        for (int x = 0; x < image.width(); ++x) {
            QColor color(image.pixel(x, y));
            int intensity = qGray(color.rgb());
            histogram[intensity]++;
        }
    }

    int maxValue = *std::max_element(histogram.constBegin(), histogram.constEnd());

    QImage histogramImage(256, maxValue, QImage::Format_RGB32);
    histogramImage.fill(Qt::white);

    QPainter painter(&histogramImage);
    painter.setPen(Qt::black);

    for (int i = 0; i < histogram.size(); ++i) {
        int height = histogram[i] * histogramImage.height() / maxValue;
        painter.drawLine(i, histogramImage.height(), i, histogramImage.height() - height);
    }

    return histogramImage;
}