histogramwidget.cpp Example File

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  #include "histogramwidget.h"
  #include <QPainter>

  HistogramWidget::HistogramWidget(QWidget *parent)
      : QWidget(parent)
      , m_levels(128)
      , m_isBusy(false)
  {
      m_processor.moveToThread(&m_processorThread);
      qRegisterMetaType<QVector<qreal> >("QVector<qreal>");
      connect(&m_processor, SIGNAL(histogramReady(QVector<qreal>)), SLOT(setHistogram(QVector<qreal>)));
      m_processorThread.start(QThread::LowestPriority);
  }

  HistogramWidget::~HistogramWidget()
  {
      m_processorThread.quit();
      m_processorThread.wait(10000);
  }

  void HistogramWidget::processFrame(QVideoFrame frame)
  {
      if (m_isBusy)
          return; //drop frame

      m_isBusy = true;
      QMetaObject::invokeMethod(&m_processor, "processFrame",
                                Qt::QueuedConnection, Q_ARG(QVideoFrame, frame), Q_ARG(int, m_levels));
  }

  void HistogramWidget::setHistogram(QVector<qreal> histogram)
  {
      m_isBusy = false;
      m_histogram = histogram;
      update();
  }

  void HistogramWidget::paintEvent(QPaintEvent *event)
  {
      Q_UNUSED(event);

      QPainter painter(this);

      if (m_histogram.isEmpty()) {
          painter.fillRect(0, 0, width(), height(), QColor::fromRgb(0, 0, 0));
          return;
      }

      qreal barWidth = width() / (qreal)m_histogram.size();

      for (int i = 0; i < m_histogram.size(); i++) {
          qreal h = m_histogram[i] * height();
          // draw level
          painter.fillRect(barWidth * i, height() - h, barWidth * (i + 1), height(), Qt::red);
          // clear the rest of the control
          painter.fillRect(barWidth * i, 0, barWidth * (i + 1), height() - h, Qt::black);
      }
  }

  void FrameProcessor::processFrame(QVideoFrame frame, int levels)
  {
      QVector<qreal> histogram(levels);

      do {
          if (!levels)
              break;

          if (!frame.map(QAbstractVideoBuffer::ReadOnly))
              break;

          if (frame.pixelFormat() == QVideoFrame::Format_YUV420P ||
              frame.pixelFormat() == QVideoFrame::Format_NV12) {
              // Process YUV data
              uchar *b = frame.bits();
              for (int y = 0; y < frame.height(); y++) {
                  uchar *lastPixel = b + frame.width();
                  for (uchar *curPixel = b; curPixel < lastPixel; curPixel++)
                      histogram[(*curPixel * levels) >> 8] += 1.0;
                  b += frame.bytesPerLine();
              }
          } else {
              QImage::Format imageFormat = QVideoFrame::imageFormatFromPixelFormat(frame.pixelFormat());
              if (imageFormat != QImage::Format_Invalid) {
                  // Process RGB data
                  QImage image(frame.bits(), frame.width(), frame.height(), imageFormat);
                  image = image.convertToFormat(QImage::Format_RGB32);

                  const QRgb* b = (const QRgb*)image.bits();
                  for (int y = 0; y < image.height(); y++) {
                      const QRgb *lastPixel = b + frame.width();
                      for (const QRgb *curPixel = b; curPixel < lastPixel; curPixel++)
                          histogram[(qGray(*curPixel) * levels) >> 8] += 1.0;
                      b = (const QRgb*)((uchar*)b + image.bytesPerLine());
                  }
              }
          }

          // find maximum value
          qreal maxValue = 0.0;
          for (int i = 0; i < histogram.size(); i++) {
              if (histogram[i] > maxValue)
                  maxValue = histogram[i];
          }

          if (maxValue > 0.0) {
              for (int i = 0; i < histogram.size(); i++)
                  histogram[i] /= maxValue;
          }

          frame.unmap();
      } while (false);

      emit histogramReady(histogram);
  }