camera.AcquisitionFrameRate.SetValue() is not accurate

[da9da9]

Describe what you want to implement and what the issue & the steps to reproduce it are: Framerate issue

I am trying to capture a sequence of still images.

I set two stages as below.
I checked that 500fps is possible from the pylon viewer.

    camera.StartGrabbing(pylon.GrabStrategy_LatestImages, pylon.GrabLoop_ProvidedByUser)
    camera.AcquisitionFrameRateEnable.SetValue(True)
    total_frames = [50, 50]  # Frames at different stages
    frame_rates = [500, 10]  # Corresponding frame rates

And I set the framerate as below. and started recording.

    camera.AcquisitionFrameRate.SetValue(frame_rates[0])

    
    height = camera.Height.GetValue()
    width = camera.Width.GetValue()
    image_Array_0 = np.empty(shape=(height, width, total_frames[0]), dtype=np.uint8)
    image_Array_1 = np.empty(shape=(height, width, total_frames[1]), dtype=np.uint8)
    while camera.IsGrabbing():
        grabResult = camera.RetrieveResult(5000, pylon.TimeoutHandling_ThrowException)
        camera.AcquisitionFrameRate.SetValue(frame_rates[0])
        if grabResult.GrabSucceeded():
            image = converter.Convert(grabResult).GetArray()
            cv2.imshow('Live View', image)

            if recording == True:
                ts = time.time()
                print(ts)
                print("recording started")
                for i in range(total_frames[0]):
                    with camera.RetrieveResult(5000) as result:
                        if grabResult.GrabSucceeded():
                            image_Array_0[:, :, i] = result.Array
                            ts = time.time()
                            print(ts)
                        else:
                            print(grabResult.ErrorDescription)
                camera.AcquisitionFrameRate.SetValue(frame_rates[1])
                print("stage1 finished")
                time.sleep(1/frame_rates[1])
                current_stage = 2
                for j in range(total_frames[1]):
                    with camera.RetrieveResult(5000) as result:
                        if grabResult.GrabSucceeded():
                            image_Array_1[:, :, j] = result.Array
                            ts = time.time()
                            print(ts)
                        else:
                            print(grabResult.ErrorDescription)
                recording = False
                captured = True
                ts = time.time()
                print(ts)
                print("recording finished")
                camera.StopGrabbing()

and below is the time difference between each frame

Stage1 (ms)		Stage2 (ms)
1.509904861		1.999855042
1.019954681		0.990152359
0000000000		0.999927521
0000000000		96.17996216
1.000165939		99.92003441
0000000000		99.99990463
1.080036163		99.81012344
2.009868622		99.97987747
3.000020981		100.8000374
0.98991394		99.17998314
2.530097961		99.98011589
2.01010704		100.2399921
1.999855042		100.219965
1.460075378		99.94006157
2.00009346		99.2898941
2.009868622		100.219965
2.00009346		99.97010231
1.989841461		100.3201008
2.00009346		99.65991974
2.079963684		100.2500057
2.660036087		100.6000042
1.260042191		99.07984734
1.999855042		100.1400948
2.350091934		99.81989861
1.71995163		100.4400253
2.00009346		100.0401974
1.929998398		99.47991371
1.999855042		99.92003441
2.390146255		100.0299454
1.519918442		100.5599499
2.089977264		99.43008423
2.089977264		99.95985031
1.640081406		99.98011589
2.259969711		100.1200676
2.01010704		100.4998684
2.169847488		99.32994843
1.830101013		100.2800465
2.009868622		99.35998917
2.75015831		100.8901596
1.749992371		99.13992882
1.489877701		101.0200977
2.00009346		99.18999672
2.009868622		100.9399891
1.99007988		98.98996353
2.140045166		100.4199982
2.009868622		99.43985939
1.550197601		100.0201702
3.010034561		100.0199318
2.009868622		100.4700661

As you can see, the stage 1 which is fast framerate is not very consistent. It must be near 2ms, but they are in the range of 1~3ms and sometimes it is even 0ms or more than 3ms
Also, the relatively slow stage 2 shows the initial framerate is very fast. and it reaches to the specified framerate.

Is my method of specifying the framerate wrong?

Is your camera operational in Basler pylon viewer on your platform

Yes

Hardware setup & camera model(s) used

acA1920-150uc
USB3 communication with PC.

Runtime information:

OS is windows 11 

pylon Viewer 64-Bit
pylon Release 7.4.0.14900
pylon C++ SDK 7.4.0.38864
pylon Application 2.1.0.14100
pylon Viewer 7.4.0.14100

python: 3.11.7 | packaged by Anaconda, Inc. | (main, Dec 15 2023, 18:05:47) [MSC v.1916 64 bit (AMD64)]
platform: win32/AMD64/10
pypylon: 3.0.1 / 7.4.0.38864

[SMA2016a]

it is not clear for me what time you want to measure? it seems to be for me that the measurement is not stable on your PC in highspeed mode.

how affect his your application? did you check the timestamp if grab result? also print block ids to see if the system loses images

[thiesmoeller]

As mentioned by @SMA2016a you measure the time when you receive the frame on your host and not when the acquisition took place.

As you are not running on a RTOS, the time when your user process wakes up ( RetrieveResult returns ) can jitter quite heavy depending on overall system load.