Thank you for your pertinent question!
I have been stupid assuming that the image was a color image.
Your simple test made me realize this obvious thing! 
Fortunately I will not die after such a shame! :-)

On Wednesday, August 19, 2020 at 3:12:16 PM UTC+2 [email protected] wrote:

> Howdy,
>
> What happens if you add the cv2 item to the view after you fully 
> initialize it?
> If you use the imread method with an image file does this work correctly?  
> This may help identify if this is an issue with the un-official openCV 
> release or pyqtgraph
> something like: 
>      import cv2 as cv
>      img = cv.imread(cv.samples.findFile("something.jpg")
>      cv.imshow("something", img)
>
> Cheers,
> J- 
>
> On Wed, Aug 19, 2020 at 8:02 AM [email protected] <[email protected]> 
> wrote:
>
>>
>> Hi All,
>>
>> I have some issues with color using pyqtgraph.
>> I have a basic code for displaying a RGBA image.
>> I am expecting to have a color image but instead I have a graylevel image
>> Do you see an obvious explanation to this behavior in this code ?
>>
>> from pyqtgraph.Qt import QtCore, QtGui
>>
>> import pyqtgraph as pg
>>
>> import cv2
>>
>>  
>>
>> pg.setConfigOptions(imageAxisOrder='row-major')
>>
>>  
>>
>> app = QtGui.QApplication([])
>>
>> ## Create window with GraphicsView widget
>>
>> win = pg.GraphicsLayoutWidget()
>>
>> win.show()  ## show widget alone in its own window
>>
>> win.setWindowTitle('pyqtgraph example: ImageItem')
>>
>> view = win.addViewBox()
>>
>> view.invertY(True)
>>
>>  
>>
>> ## lock the aspect ratio so pixels are always square
>>
>> view.setAspectLocked(True)
>>
>>  
>>
>> ## Create image item
>>
>> l_img_item = pg.ImageItem(border='w')
>>
>> view.addItem(l_img_item)
>>
>> l_img_item.setCompositionMode(QtGui.QPainter.CompositionMode_Plus)
>>
>> # l_img_item.setZValue(10)
>>
>> # l_img_item.setOpacity(0.5)
>>
>>  
>>
>> l_image = cv2.imread('_test.png')
>>
>> l_image = cv2.cvtColor(l_image, cv2.COLOR_RGBA2RGB)
>>
>>  
>>
>> ## Set initial view bounds
>>
>> view.setRange(QtCore.QRectF(0, 0, 375, 400))
>>
>>  
>>
>> # timer = QtCore.QTimer()
>>
>> # timer.timeout.connect(self._update)
>>
>> # timer.start(50)
>>
>> l_img_item.setImage(l_image, autoLevels=False)
>>
>> l_img_item.setCompositionMode(QtGui.QPainter.CompositionMode_Plus)
>>
>> app.exec_()
>>
>>
>> Thanks for your help
>>
>>
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>>
>

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