opencv BGR图像及其反向版本RGB图像[:，:，::-1]有什么区别? [英] What is the difference between an opencv BGR image and its reverse version RGB image[:,:,::-1]?

问题描述

我正在尝试显示带有QLabel的opencv图像.我得到了两个不同版本的图像，第一个是opencv BGR图像，第二个是使用image [:，:，::-1]的RGB图像，BGR版本工作正常，但RGB版本不起作用.

以下代码可以正常运行

I'm trying to show an opencv image with a QLabel. I got two different versions of the image, first one is the opencv BGR image, the second one is the RGB image using image[:,:,::-1], the BGR version works fine but the RGB version doesn't work.

The following code works fine

src = cv.imread('image.jpg')
h,w,ch = src.shape
bytesPerLine = ch * w
qImg = QImage(src.data, w, h, bytesPerLine, QImage.Format_RGB888)
qImg = qImg.rgbSwapped()
self.ui.label.setPixmap(QPixmap.fromImage(qImg))

这些代码无效:

src = cv.imread('image.jpg')
src = src[:,:,::-1]
h,w,ch = src.shape
bytesPerLine = ch * w
qImg = QImage(src.data, w, h, bytesPerLine, QImage.Format_RGB888)
self.ui.label.setPixmap(QPixmap.fromImage(qImg))

推荐答案

您已经注意到opencv读取BGR格式的图像，但是读取RGB的QImage，在第一种方法中，您无需进行转换即可转换为QImage，然后使用rgbSwapped()进行转换的方法.

As you have noticed opencv reads the image in BGR format but QImage in RGB, in your first method you convert to QImage without doing the conversion and then you use rgbSwapped() method to do the conversion.

通过测试我得到的第一种方法:

By testing the first method I get:

1000 loops, best of 5: 291 usec per loop

---

在第二种方法中，您尝试在将其转换为QImage之前执行此操作，但是当我执行它时，假设您也获得了它，则会收到以下错误消息.

---

In the second method you try to do it before converting it to QImage but when I execute it I get the following error presuming that you also get it.

Traceback (most recent call last):
  File "xxxx.py", line 18, in <module>
    qImg = QtGui.QImage(src.data, w, h, bytesPerLine, QtGui.QImage.Format_RGB888)
TypeError: arguments did not match any overloaded call:
  QImage(): too many arguments
  QImage(QSize, QImage.Format): argument 1 has unexpected type 'memoryview'
  QImage(int, int, QImage.Format): argument 1 has unexpected type 'memoryview'
  QImage(bytes, int, int, QImage.Format): argument 1 has unexpected type 'memoryview'
  QImage(sip.voidptr, int, int, QImage.Format): argument 1 has unexpected type 'memoryview'
  QImage(bytes, int, int, int, QImage.Format): argument 1 has unexpected type 'memoryview'
  QImage(sip.voidptr, int, int, int, QImage.Format): argument 1 has unexpected type 'memoryview'
  QImage(List[str]): argument 1 has unexpected type 'memoryview'
  QImage(str, format: str = None): argument 1 has unexpected type 'memoryview'
  QImage(QImage): argument 1 has unexpected type 'memoryview'
  QImage(Any): too many arguments

这是因为numpy使用memoryview来优化某些任务.在这种情况下，当进行src[:,:,::-1]优化的一种方法不是修改数据而是访问数据的方法时，这是通过

And this is because numpy uses memoryview to optimize certain tasks. And in this case when doing src[:,:,::-1] one way to optimize is not to modify the data but the way to access the data, this is done through the Buffer Protocol.

在这种情况下，QImage不支持这种类型的数据，因此解决方案是使用

And in this case QImage does not support this type of data, so the solution is to access the bytes using the tobytes() or bytes():

import cv2
from PyQt5 import QtGui, QtWidgets

if __name__ == '__main__':
    import sys
    src = cv2.imread('image.jpg')
    src = src[:,:,::-1]
    h, w, ch = src.shape
    bytesPerLine = ch * w
    qImg = QtGui.QImage(src.data.tobytes(), w, h, bytesPerLine, QtGui.QImage.Format_RGB888)
    # Or
    # qImg = QtGui.QImage(bytes(src.data), w, h, bytesPerLine, QtGui.QImage.Format_RGB888)
    app = QtWidgets.QApplication(sys.argv)
    w = QtWidgets.QLabel()
    w.setPixmap(QtGui.QPixmap.fromImage(qImg))
    w.show()
    sys.exit(app.exec_())

时间:

500 loops, best of 5: 523 usec per loop

---

另一种解决方案是使用opencv的cvtColor()函数，如果您修改数据，则该函数:

---

Another solution is to use the cvtColor() function of opencv that if you modify the data:

import cv2
from PyQt5 import QtGui, QtWidgets

if __name__ == '__main__':
    import sys
    src = cv2.imread('image.jpg')
    src = cv2.cvtColor(src, cv2.COLOR_BGR2RGB)
    h, w, ch = src.shape
    bytesPerLine = ch * w
    qImg = QtGui.QImage(src.data, w, h, bytesPerLine, QtGui.QImage.Format_RGB888)
    app = QtWidgets.QApplication(sys.argv)
    w = QtWidgets.QLabel()
    w.setPixmap(QtGui.QPixmap.fromImage(qImg))
    w.show()
    sys.exit(app.exec_())

时间:

1000 loops, best of 5: 263 usec per loop

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