ImageItem#

Overview#

ImageItem displays images inside a GraphicsView, or a ViewBox, which may itself be part of a PlotItem. It is designed for rapid updates as needed for a video display. The supplied data is optionally scaled (see ImageItem.setLevels) and/or colored according to a lookup table (see ImageItem.setColorMap and ImageItem.setLookupTable).

Data is provided as a NumPy array with an ordering of either

col-major, where the shape of the array represents (width, height) or
row-major, where the shape of the array represents (height, width).

While col-major is the default, row-major ordering typically has the best performance. In either ordering, a third dimension can be added to the array to hold individual [R,G,B] or [R,G,B,A] channels/components.

Notes#

ImageItem is frequently used in conjunction with ColorBarItem to provide a color map display and interactive level adjustments, or with HistogramLUTItem or HistogramLUTWidget for a full GUI to control the levels and lookup table used to display the image.

An image can be placed into a plot area of a given extent directly through the ImageItem.setRect method or the rect keyword. This is internally realized through assigning a QTransform. For other translation, scaling or rotations effects that persist for all later image data, the user can also directly define and assign such a transform, as shown in the example below.

Performance#

The performance of ImageItem can vary significantly based on attributes of the image, levels and lut input arguments. It should not be assumed that the default parameters are the most performant, as the default values are largely there to preserve backwards compatibility.

The following guidance should be observed if performance is an important factor

Instantiate ImageItem with axisOrder='row-major'
- Alternatively, set the global configuration optionally pyqtgraph.setConfigOption('imageAxisOrder', 'row-major')
Use C-contiguous image data.
For 1 or 3 channel data, use uint8, uint16, float32, or float64 image dtype.
For 4-channel data, use uint8 or uint16 with levels=None.
levels should be set to either to None or to single channel [min, max]
- Not setting levels will trigger autoLevels sampling
If using LUTs (lookup tables), ensure they have a dtype of uint8 and have 256 points or less. That can be accomplished with calling:
- ImageItem.setColorMap or
- ImageItem.setLookupTable with ColorMap.getLookupTable(nPts=256) (default is nPts=512)
For floating point image arrays, prefer float32 dtype to float64 and avoid NaN values.
Enable Numba with pyqtgraph.setConfigOption('useNumba', True)
- JIT compilation will only accelerate repeated image display.

Internally, pyqtgraph attempts to directly construct a QImage using a combination of QImage.Format options and QImage.setColorTable if necessary. This does not work in all cases that pyqtgraph supports. If pyqtgraph is unable to construct the QImage in such a fashion, it will fall back on makeARGB() to manipulate the data in a manner that QImage can read it in. There is a significant performance penalty when having to use makeARGB().

For applications that are very performance sensitive, every effort should be made so that the arguments passed to ImageItem.setImage do not call makeARGB().

Examples#

Scale and Position ImageItem#

In the following example, it is demonstrated how a user scale and translate a ImageItem within a ViewBox to occupy a specific position and size.

import numpy as np
import pyqtgraph as pg
import pyqtgraph.exporters as exp
from pyqtgraph.Qt import QtGui, mkQApp

mkQApp("ImageItem transform example")

class MainWindow(pg.GraphicsLayoutWidget):
    """ example application main window """
    def __init__(self):
        super().__init__()
        self.resize(440,400)
        self.show()

        plot = self.addPlot()

        # Set To Larger Font
        leftAxis = plot.getAxis('left')
        bottomAxis = plot.getAxis('bottom')
        font = QtGui.QFont("Roboto", 18)
        leftAxis.setTickFont(font)
        bottomAxis.setTickFont(font)

        # Example: Transformed display of ImageItem
        tr = QtGui.QTransform()  # prepare ImageItem transformation:
        tr.scale(6.0, 3.0)       # scale horizontal and vertical axes
        tr.translate(-1.5, -1.5) # move 3x3 image to locate center at axis origin

        img = pg.ImageItem(
            image=np.eye(3),
            levels=(0,1)
        ) # create example image
        img.setTransform(tr) # assign transform

        plot.addItem( img )  # add ImageItem to PlotItem
        plot.showAxes(True)  # frame it with a full set of axes
        plot.invertY(True)   # vertical axis counts top to bottom

        self.timer = pg.QtCore.QTimer( singleShot=True )
        self.timer.timeout.connect(self.export)
        self.timer.start(100)

Inheritance#

API#

class pyqtgraph.ImageItem(

image: ndarray | None = None,

**kargs,

)[source]#

Graphics object used to display image data.

ImageItem can render images with 1, 3 or 4 channels, use lookup tables to apply false colors to images, and users can either set levels limits, or rely on the auto-sampling.

Performance can vary wildly based on the attributes of the inputs provided, see performance for guidance if performance is an important factor.

There is optional numba and cupy support.

Bases: pyqtgraph.GraphicsObject

Parameters:

image (numpy.ndarray or None, default None) – Image data.
**kargs (dict, optional) – Arguments directed to setImage and setOpts, refer to each method for documentation for possible arguments.

Signals:

sigImageChanged (Signal) – Emitted when the image is changed.
sigRemoveRequested (Signal) – Emitted when there is a request to remove the image. Signal emits the instance of the ImageItem whose removal is requested.

See also

setImage: For descriptions of available keyword arguments.
setOpts: For information on supported formats.

clear()[source]#: Clear the assigned image.

getColorMap() → ColorMap | None[source]#

Retrieve the ColorMap object currently used.

Returns:: The assigned ColorMap, or None if not available.
Return type:: ColorMap or None

getHistogram(

bins: str | int = 'auto',

step: str | generic = 'auto',

perChannel: bool = False,

targetImageSize: int = 200,

**kwargs,

) → list[tuple[ndarray, ndarray]] | tuple[ndarray, ndarray] | tuple[None, None][source]#

Generate arrays containing the histogram values.

Similar to numpy.histogram()

Parameters:

bins (int or str, default 'auto') – The bins argument and any extra keyword arguments are passed to numpy.histogram(). If bins == 'auto', a bin number is automatically chosen based on the image characteristics.
step (int or str, default 'auto') – The step argument causes pixels to be skipped when computing the histogram to save time. If step is ‘auto’, then a step is chosen such that the analyzed data has dimensions approximating targetImageSize for each axis.
perChannel (bool, default False) – If True, then a histogram is computed for each channel, and the output is a list of the results.
targetImageSize (int, default 200) – This parameter is used if step == 'auto', If so, the step size is calculated by step = ceil(image.shape[0] / targetImageSize).
**kwargs (dict, optional) – Dictionary of arguments passed to numpy.histogram().

Returns:

Returns x and y arrays containing the histogram values for the current image. For an explanation of the return format, see numpy.histogram(). Returns [(numpy.ndarray, numpy.ndarray),...] if perChannel=True, one element per channel. Returns (None, None) is there is no image, or image size is 0.

Return type:

numpy.ndarray, numpy.ndarray or None, None or list of tuple of numpy.ndarray, numpy.ndarray

Warns:

RuntimeWarning – Emits when targetHistogramSize argument is passed in, which does nothing.

See also

numpy.histogram: Describes return format in greater detail.
numpy.histogram_bin_edges: Details the different string values accepted as the bins parameter.

getLevels() → ndarray | None[source]#

Return the array representing the current level settings.

See setLevels(). When autoLevels is active, the format is [blackLevel, whiteLevel].

Returns:: The value that the levels are set to.
Return type:: numpy.ndarray or None

nanPolicy() → str[source]#

Retrieve the string representing the current NaN policy.

See :meth:setNanPolicy.

Returns:: The NaN policy that this ImageItem uses during downsampling.
Return type:: {'propagate', 'omit'}

pixelSize() → tuple[float, float][source]#

Get the x and y size of each pixel in the view coordinate system.

Returns:: The x and y size of each pixel in scene space.
Return type:: float, float

quickMinMax( targetSize: int = 1000000, ) → tuple[float, float][source]#

Estimate the min and max values of the image data by sub-sampling.

Sampling is performed at regular strides chosen to evaluate a number of samples equal to or less than targetSize. Returns the estimated min and max values of the image data.

Parameters:: targetSize (int, default 1_000_000) – The number of pixels to downsample the image to.
Returns:: Estimated minimum and maximum values of the image data.
Return type:: float, float

save( fileName: str | Path, *args, ) → None[source]#

Save this image to file.

Note that this saves the visible image, after scale/color changes, not the original data.

Parameters:

fileName (os.PathLike) – File path to save the image data to.
*args (tuple) – Arguments that are passed to QImage.save.

Return type:

None

See also

QImage.save :: *args is relayed to this method.

setAutoDownsample( active: bool = True, )[source]#

Control automatic downsampling for this ImageItem.

Parameters:: active (bool, default True) – If active is True, the image is automatically downsampled to match the screen resolution. This improves performance for large images and reduces aliasing. If autoDownsample is not specified, then ImageItem will choose whether to downsample the image based on its size. False disables automatic downsampling.

setBorder( b, )[source]#

Define the color of the border drawn around the image.

Parameters:: b (color_like) – Accepts all arguments supported by mkPen().

setColorMap( colorMap: ColorMap | str, )[source]#

Set a color map for false color display of a monochrome image.

Parameters:: colorMap (ColorMap or str) – A string argument will be passed to colormap.get().
Raises:: TypeError – Raised when colorMap is not of type str or ColorMap.

setCompositionMode( mode: CompositionMode, )[source]#

Change the composition mode of the item, useful when overlaying multiple items.

Parameters:

mode (QPainter.CompositionMode) – Composition of the item, often used when overlaying items. Common options include:

QPainter.CompositionMode.CompositionMode_SourceOver Image replaces the background if it is opaque. Otherwise, it uses the alpha channel to blend the image with the background, default.
QPainter.CompositionMode.CompositionMode_Overlay Image color is mixed with the background color to reflect the lightness or darkness of the background.
QPainter.CompositionMode.CompositionMode_Plus Both the alpha and color of the image and background pixels are added together.
QPainter.CompositionMode.CompositionMode_Plus The output is the image color multiplied by the background.

See QPainter.CompositionMode in the Qt documentation for more options and details.

See also

QPainter.CompositionMode :: Details all the possible composition mode options accepted.

setImage(

image: ndarray | None = None,

autoLevels: bool | None = None,

levelSamples: int = 65536,

**kwargs,

)[source]#

Update the image displayed by this ImageItem.

All keywords supported by setOpts() are also allowed here.

Parameters:

image (numpy.ndarray or None, default None) – Image data given as NumPy array with an integer or floating point dtype of any bit depth. A 2-dimensional array describes single-valued (monochromatic) data. A 3-dimensional array is used to give individual color components. The third dimension must be of length 3 (RGB) or 4 (RGBA). np.nan values are treated as transparent pixels.
autoLevels (bool or None, default None) – If True, ImageItem will automatically select levels based on the maximum and minimum values encountered in the data. For performance reasons, this search sub-samples the images and may miss individual bright or dark points in the data set. If False, the search will be omitted. If None, and the levels keyword argument is given, it will switch to False, if the levels argument is omitted, it will switch to True.
levelSamples (int, default 65536) – Only used when autoLevels is None. When determining minimum and maximum values, ImageItem only inspects a subset of pixels no larger than this number. Setting this larger than the total number of pixels considers all values. See quickMinMax.
**kwargs (dict, optional) – Extra arguments that are passed to setOpts.

See also

quickMinMax: See this method for how levelSamples value is utilized.
pyqtgraph.functions.makeARGB(): See this function for how image data is modified prior to rendering.

Notes

For backward compatibility, image data is assumed to be in column-major order (column, row) by default. However, most data is stored in row-major order (row, column). It can either be transposed before assignment

imageitem.setImage(imagedata.T)

or the interpretation of the data can be changed locally through the axisOrder keyword or by changing the imageAxisOrder global configuration option.

Set image scaling levels.

Calling this method, even with levels=None will disable auto leveling which is equivalent to setImage() with autoLevels=False.

Parameters:

levels (array_like or None) – Sets the numerical values that correspond to the limits of the color range.
- [blackLevel, whiteLevel]
  sets black and white levels for monochrome data and can be used with a lookup table.
- [[minR, maxR], [minG, maxG], [minB, maxB]]
  sets individual scaling for RGB values. Not compatible with lookup tables.
- None
  Disables the application of levels, but setting to None prevents the auto-levels mechanism from sampling the image. Not compatible with images that use floating point dtypes.
update (bool, default True) – Update the image immediately to reflect the new levels.

See also

pyqtgraph.functions.makeARGB: For more details on how levels are applied.

Set lookup table lut to use for false color display of a monochrome image.

Ordinarily, this table is supplied by a HistogramLUTItem, GradientEditorItem or ColorBarItem.

Parameters:

lut (array_like or Callable) – If lut is an np.ndarray, ensure the dtype is np.uint8. Alternatively can be a callable that accepts the current image as an argument and returns the lookup table to use. Support for callable will be removed in a future version of pyqtgraph.
update (bool, default True) – Update the intermediate image.

See also

pyqtgraph.functions.makeARGB(): See this function for more information on how this is used.
ColorMap.getLookupTable: Can construct a lookup table from a ColorMap object.

Notes

For performance reasons, if not passing a callable, every effort should be made to keep the number of entries to <= 256.

setNanPolicy( nanPolicy: str, )[source]#

Control how NaN values are handled during downsampling for this ImageItem.

Parameters:: nanPolicy ({'propagate', 'omit'}) – If ‘nanPolicy’ is ‘ignore’, NaNs are automatically ignored during downsampling, at the expense of performance. If ‘nanPolicy’ is ‘propagate’, NaNs are kept during downsampling. Unless a different policy was specified, a new ImageItem is created with nanPolicy='propagate'.

setOpts(

update: bool = True,

**kwargs,

)[source]#

Set display and processing options for this ImageItem.

ImageItem and setImage() support all keyword arguments listed here.

Parameters:

update (bool, default True) – Controls if image immediately updates to reflect the new options.
**kwargs (dict, optional) – Extra arguments that are directed to the respective methods. Expected keys include:
- autoDownsample whose value is directed to setAutoDownsample()
- nanPolicy whose value is directed to setNanPolicy()
- axisOrder, which needs to be one of {‘row-major’, ‘col-major’}, determines the relationship between the numpy axis and visual axis of the data.
- border, whose value is directed to setBorder()
- colorMap, whose value is directed to setColorMap()
- compositionMode, whose value is directed to setCompositionMode()
- levels whose value is directed to setLevels()
- lut, whose value is directed to setLookupTable()
- opacify whose value is directed to QGraphicsItem.setOpacity
- rect whose value is directed to setRect()
- removable boolean, determines if the context menu is available

See also

setAutoDownsample(): Accepts the value of kwargs['autoDownsample'].
setNanPolicy(): Accepts the value of kwargs['nanPolicy'].
setBorder(): Accepts the value of kwargs['border'].
setColorMap(): Accepts the value of kwargs['colorMap'].
setCompositionMode(): Accepts the value of kwargs['compositionMode'].
setImage(): Accepts the value of kwargs['image'].
setLevels(): Accepts the value of kwargs['levels'].
setLookupTable(): Accepts the value of kwargs['lut'].
QGraphicsItem.setOpacity: Accepts the value of kwargs['opacity'].
setRect(): Accepts the value of kwargs['rect'].

setPxMode( b: bool, )[source]#

Set whether item ignores transformations and draws directly to screen pixels.

Parameters:: b (bool) – If True, the item will not inherit any scale or rotation transformations from its parent items, but its position will be transformed as usual.

See also

QGraphicsItem.GraphicsItemFlag :: Read the description of ItemIgnoresTransformations for more information.

setRect( *args, )[source]#

Set view rectangle for the ImageItem to occupy.

In addition to accepting a QRectF, you can pass the numerical values representing the x, y, w, h, where x, y represent the x, y coordinates of the top left corner, and w and h represent the width and height respectively.

Parameters:: *args (tuple) – Contains one of QRectF, QRect, or arguments that can be used to construct QRectF.

See also

QRectF: See constructor methods for allowable *args.

Notes

This method cannot be used before an image is assigned. See the examples for how to manually set transformations.