pyqtgraph中的matplotlib.pyplot.clim对应物

Question

我只想将色彩映射表(“热”)应用于图像的特定范围的值。我已经在matplotlib.pyplot.clim中了解了这个功能，您必须指定缩放的最小值和最大值。据我所知，您应该使用setLevels(min，max)来完成此任务。我已经包含了一个最小的例子，它表明不幸的是这两种表示不是等价的。

import matplotlib.pyplot as plt
from matplotlib import cm
import numpy as np
import os
import pyqtgraph as pg
from pyqtgraph.Qt import QtCore, QtGui#, QtWidgets
#import PyQt5.QtCore
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QWidget, QMainWindow, QPushButton, QFileDialog, \
    QScrollArea, QVBoxLayout, QGroupBox, QLabel, QFormLayout, QComboBox, QHBoxLayout
from skimage import io    
import sys


def main():
    imarray = np.random.rand(100, 100) * 515
    imarray = np.clip(imarray, 0, 515)
    plt_example(imarray)
    pyqtgraph_example(imarray)

def plt_example(data):
    plt.imshow(data, cmap='hot')
    c = plt.colorbar()
    plt.clim(0, 200)
    plt.show()


def pyqtgraph_example(data):
    colormap = cm.get_cmap("hot")
    colormap._init()
    lut = (colormap._lut * 255).view(np.ndarray)
    app = pg.mkQApp("Test")

    
    win = pg.GraphicsLayoutWidget()
    win.show()
    win.setWindowTitle('pyqtgraph example: ImageItem')
    view = win.addViewBox()

    ## lock the aspect ratio so pixels are always square
    view.setAspectLocked(True)

    ## Create image item
    img = pg.ImageItem()
    view.addItem(img)

    img.setImage(data)
    img.setLevels([0, 200]) # same functionality as clim?
    img.setLookupTable(lut)

    app.exec()

if __name__ == "__main__":
    main()

你知道如何在pyqtgraph中获得与matplotlib中的clim相同的表示吗？第一张图片显示了使用matplotlib的结果，第二张图片显示了使用pyqtgraph的结果。

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Answer 1

这个问题出现在pyqtgraph的问题跟踪器上：https://github.com/pyqtgraph/pyqtgraph/pull/1985#issuecomment-932223288

下面是在两个库之间生成相同结果的一些代码

import matplotlib.pyplot as plt
import numpy as np
import pyqtgraph as pg

def main():
    imarray = np.random.rand(100, 100) * 515
    imarray = np.clip(imarray, 0, 515)
    plt_example(imarray)
    pyqtgraph_example(imarray)

def plt_example(data):
    plt.imshow(data, cmap='hot')
    c = plt.colorbar()
    plt.clim(0, 200)
    plt.show(block=False)

def pyqtgraph_example(data):
    app = pg.mkQApp("Test")
    win = pg.GraphicsLayoutWidget()
    win.setWindowTitle('pyqtgraph example: ImageItem')
    win.show()

    # add plot with correct axis orientation and locked aspect ratio
    plot = win.addPlot()
    plot.setAspectLocked(True)
    plot.invertY()

    # Create image item
    img = pg.ImageItem(data, axisOrder='row-major')
    plot.addItem(img)

    # Create color bar and have it control image levels    
    cmap = pg.colormap.getFromMatplotlib('hot')
    cbi = pg.ColorBarItem(colorMap=cmap)
    cbi.setImageItem(img, insert_in=plot)
    cbi.setLevels([0, 200]) # colormap range

    app.exec()

if __name__ == "__main__":
    main()

问题跟踪器中这段代码的发帖者指出，在matplotlib中，"overflow“值似乎呈现为白色，而在pyqtgraph中呈现为黑色。此外，由于未设置轴顺序并且y轴可能颠倒，因此pyqtgraph图像向左旋转了90度。

为了获得正确的旋转方向，代码有两行说明

plot.invertY()

和

pg.ImageItem(data, axisOrder='row-major')

希望这能有所帮助！