Use an image as background for 2D data

[Simon Hafner]

Hello

I'm looking for a way to use an image as background to plot data onto. The data consists of lines. With matplotlib, I achieved this effect using `imshow`. Is there a similar method in pyqtgraph? I considered stacking an ImageView onto a graph, but I haven't found how to stack widgets yet.

Cheers

[Karl Bedrich]

hey simon,

i use this code (shorted) to add an image to the top:

img = QtGui.QImage(filepath)#.scaled(self._img_res[0],self._img_res[1],
 #transformMode=QtCore.Qt.SmoothTransformation).mirrored(vertical=True)
try:
 #thats essential for pg.imageToArray(img)
 img = img.convertToFormat(QtGui.QImage.Format_ARGB32_Premultiplied)
 imgArray = pg.imageToArray(img, copy=True)
 if not self._img:
 self._img = pg.ImageItem(imgArray)
 else:
 self._img.setImage(imgArray)
 #self._img.setRect(self._imgRect)
 #self._img.setOpacity(self.pImageOpacity.value())
except AttributeError:
 print "Image not valid!"
 return False
#add the img to the viewbox of your plot:
self.display.view.vb.addItem(self._img)

bye,

karl

[Luke Campagnola]

On Mon, Dec 2, 2013 at 2:15 AM, Simon Hafner <react...@gmail.com> wrote:

Hello

I'm looking for a way to use an image as background to plot data onto. The data consists of lines. With matplotlib, I achieved this effect using `imshow`. Is there a similar method in pyqtgraph? I considered stacking an ImageView onto a graph, but I haven't found how to stack widgets yet.

You can add an ImageItem directly to a PlotItem or PlotWidget, then use ImageItem.scale, .translate, or .setRect to change the boundaries of the image relative to the plot data:

import pyqtgraph as pg

plt = pg.plot([1,5,2,4,3], pen='r')

img_data = pg.np.random.normal(size=(100,100))

img = pg.ImageItem(img_data)

plt.addItem(img)

img.setZValue(-100)  # make sure image is behind other data

img.setRect(pg.QtCore.QRectF(0, 0, 4, 5))

img.setLevels([0, 10])  # make image appear a bit darker

Karl's example is similar to this, and also shows how to load image data from a file.

Alternately, you could keep the ImageView and add a PlotDataItem to its internal ViewBox. 

Luke

[Tom Jordan]

Luke,

Thanks for providing a complete example. Your code works correctly. However, I would like to set a png image (it's a map) as the background of a plot.

When I run combine your code with Karl's to load a png from file, I get the exception below:

from pyqtgraph.Qt import QtGui

import pyqtgraph as pg

plt = pg.plot([1,5,2,4,3], pen='r')

img = QtGui.QImage('c:\Temp\solar-terminator-fig.png')

img = img.convertToFormat(QtGui.QImage.Format_ARGB32_Premultiplied)

imgArray = pg.imageToArray(img, copy=True)

imgitem = pg.ImageItem(imgArray)

plt.addItem(imgitem)

imgitem.setZValue(-100)  # make sure image is behind other data

imgitem.setRect(pg.QtCore.QRectF(0, 0, 4, 5))

imgitem.setLevels([0, 10])  # make image appear a bit darker

Traceback (most recent call last):

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\functions.py", line 790, in rescaleData

    raise Exception('Weave is disabled; falling back to slower version.')

Exception: Weave is disabled; falling back to slower version.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\graphicsItems\ImageItem.py", line 309, in paint

    self.render()

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\graphicsItems\ImageItem.py", line 301, in render

    argb, alpha = fn.makeARGB(image.transpose((1, 0, 2)[:image.ndim]), lut=lut, levels=self.levels)

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\functions.py", line 942, in makeARGB

    data = rescaleData(data, scale/(maxVal-minVal), minVal, dtype=int)

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\functions.py", line 828, in rescaleData

    d2 *= scale

TypeError: Cannot cast ufunc multiply output from dtype('float64') to dtype('uint8') with casting rule 'same_kind'

Traceback (most recent call last):

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\functions.py", line 790, in rescaleData

    raise Exception('Weave is disabled; falling back to slower version.')

[Luke Campagnola]

On Tue, Jul 19, 2016 at 7:41 AM, Tom Jordan <flacy...@gmail.com> wrote:

Traceback (most recent call last):

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\graphicsItems\ImageItem.py", line 309, in paint

    self.render()

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\graphicsItems\ImageItem.py", line 301, in render

    argb, alpha = fn.makeARGB(image.transpose((1, 0, 2)[:image.ndim]), lut=lut, levels=self.levels)

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\functions.py", line 942, in makeARGB

    data = rescaleData(data, scale/(maxVal-minVal), minVal, dtype=int)

  File "C:\apps\Anaconda3\lib\site-packages\pyqtgraph\functions.py", line 828, in rescaleData

    d2 *= scale

TypeError: Cannot cast ufunc multiply output from dtype('float64') to dtype('uint8') with casting rule 'same_kind'

There was a recent API change in numpy that causes this error. It is corrected in the develop branch on github.