PyQtGraph窗口调整大小时ImageItem颜色映射重置为灰度问题

问题描述 #

使用PyQt66.4.2、pyqtgraph0.13.3时，调整GraphicsLayoutWidget窗口大小，ImageItem的颜色映射会重置为灰度。初始窗口正常显示CET-R4颜色映射，但窗口resize或滑动HistogramLUTItem的渐变编辑器时，图像会变为灰度；移除hist.setImageItem(img)语句后，颜色映射不再变化。

相关代码：

# PyQt6==6.4.2
# pyqtgraph==0.13.3

import numpy as np
import pyqtgraph as pg
from pyqtgraph.Qt import QtGui


# Interpret image data as row-major instead of col-major
pg.setConfigOptions(imageAxisOrder='row-major')

pg.mkQApp()
win = pg.GraphicsLayoutWidget()

# A plot area (ViewBox + axes) for displaying the image
p1 = win.addPlot(title="")

# Item for displaying image data
img = pg.ImageItem()
p1.addItem(img)

# Contrast/color control
hist = pg.HistogramLUTItem()
hist.setImageItem(img) # removing this line prevents the colorMap from changing when resizing the window
win.addItem(hist)

# Generate image data
data = np.random.normal(size=(200, 100))
img.setImage(data)
img.setColorMap(pg.colormap.get('CET-R4'))
hist.setLevels(data.min(), data.max())

win.show()


if __name__ == '__main__':
    pg.exec()

原因分析 #

这是pyqtgraph 0.13.3版本的已知Bug，不是操作错误。当HistogramLUTItem与ImageItem关联后，窗口resize或操作渐变编辑器时，HistogramLUTItem会自动将ImageItem的颜色映射重置为默认的灰度映射，覆盖之前设置的自定义颜色映射。

修复/规避方法 #

方法1：调整设置顺序，同步颜色映射 #

先给ImageItem设置颜色映射，再同步设置HistogramLUTItem的颜色映射，最后关联两者。修改后的代码如下：

# PyQt6==6.4.2
# pyqtgraph==0.13.3

import numpy as np
import pyqtgraph as pg
from pyqtgraph.Qt import QtGui


# Interpret image data as row-major instead of col-major
pg.setConfigOptions(imageAxisOrder='row-major')

pg.mkQApp()
win = pg.GraphicsLayoutWidget()

# A plot area (ViewBox + axes) for displaying the image
p1 = win.addPlot(title="")

# Item for displaying image data
img = pg.ImageItem()
p1.addItem(img)

# Contrast/color control
hist = pg.HistogramLUTItem()

# Generate image data
data = np.random.normal(size=(200, 100))
img.setImage(data)

# 先获取并设置颜色映射
cmap = pg.colormap.get('CET-R4')
img.setColorMap(cmap)
hist.setColorMap(cmap)  # 同步直方图的颜色映射

# 再关联ImageItem
hist.setImageItem(img)
win.addItem(hist)

hist.setLevels(data.min(), data.max())

win.show()


if __name__ == '__main__':
    pg.exec()

方法2：升级pyqtgraph版本 #

该Bug在pyqtgraph 0.14.0及以上版本中已被修复，直接升级到最新稳定版即可解决问题。可以用pip命令升级：

pip install --upgrade pyqtgraph

方法3：手动监听resize事件重置颜色映射（不推荐） #

如果无法升级版本，可以监听窗口的resize事件，在窗口大小变化后重新设置颜色映射。但这种方法需要额外处理信号，不如前两种方法简洁可靠，示例代码如下：

# 在原代码基础上添加以下内容
def reset_colormap():
    img.setColorMap(pg.colormap.get('CET-R4'))

# 绑定窗口resize事件
win.resizeEvent = lambda event: (QtGui.QWidget.resizeEvent(win, event), reset_colormap())

内容的提问来源于stack exchange，提问作者Teun