Capturing Image Data

To capture an image an instance of the class mvIMPACT.acquire.FunctionInterface must be created. This class can be constructed by passing a pointer to the mvIMPACT.acquire.Device object obtained from the mvIMPACT.acquire.DeviceManager to the class constructor.

The function interface class provides access to most of the devices executable functions, while most of the settings (e.g. the exposure time or the trigger mode) are implemented as properties (see e.g. mvIMPACT.acquire.Property for details).

This is how a continuous acquisition from a user selected device can be achieved:

import os, platform, sys
# import all the stuff from our SDK into the current scope
from mvIMPACT import acquire
# import all the helper functions for the examples using our SDK such as 'conditionalSetProperty' into the current scope
# If you want to use this module in your code feel free to do so but make sure the 'Common' folder resides in a sub-folder of your project then
from mvIMPACT.Common import exampleHelper
 
# For systems with NO mvDisplay library support
#import ctypes
#import Image
#import numpy
 
devMgr = acquire.DeviceManager()
pDev = exampleHelper.getDeviceFromUserInput(devMgr)
if pDev == None:
    exampleHelper.requestENTERFromUser()
    sys.exit(-1)
pDev.open()
 
print("Please enter the number of buffers to capture followed by [ENTER]: ", end='')
framesToCapture = exampleHelper.getNumberFromUser()
if framesToCapture < 1:
    print("Invalid input! Please capture at least one image")
    sys.exit(-1)
 
# The mvDisplay library is only available on Windows systems for now
isDisplayModuleAvailable = platform.system() == "Windows"
if isDisplayModuleAvailable:
    display = acquire.ImageDisplayWindow("A window created from Python")
else:
    print("The display library of this SDK is not available on this('" + platform.system() + "') system. Consider using the PIL(Python Image Library) and numpy(Numerical Python) packages instead. Have a look at the source code of this application to get an idea how.")
 
fi = acquire.FunctionInterface(pDev)
statistics = acquire.Statistics(pDev)
 
while fi.imageRequestSingle() == acquire.DMR_NO_ERROR:
    print("Buffer queued")
pPreviousRequest = None
 
exampleHelper.manuallyStartAcquisitionIfNeeded(pDev, fi)
for i in range(framesToCapture):
    requestNr = fi.imageRequestWaitFor(10000)
    if fi.isRequestNrValid(requestNr):
        pRequest = fi.getRequest(requestNr)
        if pRequest.isOK:
            if i%100 == 0:
                print("Info from " + pDev.serial.read() +
                         ": " + statistics.framesPerSecond.name() + ": " + statistics.framesPerSecond.readS() +
                         ", " + statistics.errorCount.name() + ": " + statistics.errorCount.readS() +
                         ", " + statistics.captureTime_s.name() + ": " + statistics.captureTime_s.readS())
            if isDisplayModuleAvailable:
                display.GetImageDisplay().SetImage(pRequest)
                display.GetImageDisplay().Update()
            # For systems with NO mvDisplay library support
            #cbuf = (ctypes.c_char * pRequest.imageSize.read()).from_address(int(pRequest.imageData.read()))
            #channelType = numpy.uint16 if pRequest.imageChannelBitDepth.read() > 8 else numpy.uint8
            #arr = numpy.fromstring(cbuf, dtype = channelType)
            #arr.shape = (pRequest.imageHeight.read(), pRequest.imageWidth.read(), pRequest.imageChannelCount.read())
 
            #if channelCount == 1:
            #    img = Image.fromarray(arr)
            #else:
            #    img = Image.fromarray(arr, 'RGBA' if alpha else 'RGB')
        if pPreviousRequest != None:
            pPreviousRequest.unlock()
        pPreviousRequest = pRequest
        fi.imageRequestSingle()
    else:
        # Please note that slow systems or interface technologies in combination with high resolution sensors
        # might need more time to transmit an image than the timeout value which has been passed to imageRequestWaitFor().
        # If this is the case simply wait multiple times OR increase the timeout(not recommended as usually not necessary
        # and potentially makes the capture thread less responsive) and rebuild this application.
        # Once the device is configured for triggered image acquisition and the timeout elapsed before
        # the device has been triggered this might happen as well.
        # The return code would be -2119(DEV_WAIT_FOR_REQUEST_FAILED) in that case, the documentation will provide
        # additional information under TDMR_ERROR in the interface reference.
        # If waiting with an infinite timeout(-1) it will be necessary to call 'imageRequestReset' from another thread
        # to force 'imageRequestWaitFor' to return when no data is coming from the device/can be captured.
        print("imageRequestWaitFor failed (" + str(requestNr) + ", " + acquire.ImpactAcquireException.getErrorCodeAsString(requestNr) + ")")
exampleHelper.manuallyStopAcquisitionIfNeeded(pDev, fi)
exampleHelper.requestENTERFromUser()

This sample contains everything the user needs to do to continuously capture images including all initialization work and error handling for every source of error one can think of.

Note

A much more specific summary of the available sample applications can be found at the Typical Usage Scenarios And Example Applications page.

Several example applications will provide an even better understanding of the interface.

The 'GenICam' vs. 'DeviceSpecific' Interface Layout chapter will provide more details on how to work with properties.