# How to acquiring only the latest image from the buffer

**URL:** <https://forum.commonvisionblox.com/t/how-to-acquiring-only-the-latest-image-from-the-buffer/1061>\
**Category:** Python API\
**Created:** [February 19, 2020, 10:11am UTC](https://forum.commonvisionblox.com/t/how-to-acquiring-only-the-latest-image-from-the-buffer/1061 "2020-02-19T10:11:05Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![piotrM](https://avatars.discourse-cdn.com/v4/letter/p/d07c76/32.png) [@piotrM](https://forum.commonvisionblox.com/u/piotrM)\
**Post date:** [February 19, 2020, 10:11am UTC](https://forum.commonvisionblox.com/t/how-to-acquiring-only-the-latest-image-from-the-buffer/1061/1 "2020-02-19T10:11:05Z")

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Hi,

I am working with 4 cameras that are being triggered from PLC every 0.3-0.6 sec depending on how we set it. Sometimes 2 frames are grabbed and I when I use stream.wait() I receive the second photo form the last trigger and not the current photo. The result is that 2 cameras show latest photo and 2 might have the old one.

Can I somehow clear the buffer on ensure that I am getting the latest photo when using stream.wait()? I was trying to use ring\_buffer.lock\_mode to lock the buffer and access the last buffer photo but I have no idea how to access the latest photo and when to call stream.wait() in that situation.

I was also trying the Acquisition mode as single frame but I don’t know how to exactly use it and if it is even a way to go.

Or maybe I can manually somehow clear the camera buffer?

Thanks!  
Piotr

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**Author:** ![parsd](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.commonvisionblox.com/parsd/32/7_2.png) [@parsd](https://forum.commonvisionblox.com/u/parsd)\
**Post date:** [February 25, 2020, 1:11pm UTC](https://forum.commonvisionblox.com/t/how-to-acquiring-only-the-latest-image-from-the-buffer/1061/2 "2020-02-25T13:11:21Z")

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Hi @piotrM,

sorry for the late reply. This function should do what you want:

```auto
import typing
import cvb

def wait_for_newest(stream: cvb.Stream, time_span: typing.Optional[int] = None) -> typing.Tuple[cvb.StreamImage, cvb.WaitStatus]:
    while True:
        image, status = stream.wait() if time_span is None else stream.wait_for(time_span)
        num_pending = stream.statistics[cvb.StreamInfo.NumBuffersPending]
        if status is not cvb.WaitStatus.Ok or num_pending == 0:
            return image, status

```

So you could use this either like `wait_for_newest(device.stream)` or add it to the methods of your current stream (assuming your `cvb.Device` is _device_) via Python’s descriptor protocol:

```auto
device.stream.wait_for_newest = wait_for_newest. __get__ (device.stream)

```

Then you can call `device.stream.wait_for_newest()` directly. But keep in mind that you have to do the assignment for every new `cvb.Stream` object you create via `cvb.DeviceFactory.open`…

This is for usage with lockmode auto, though. Which is perfect for the use case you have in mind. It works, because `stream.wait` returns immediately if there is still an image in the ring buffer (num buffers pending \> 0).

**Attention:**  
You still must be, or make sure that you are in sync with your triggers. Not that you get in an overlap scenario where you get 4 images of the current batch and one from the next batch. Or what happens if a frame of one of the cameras is dropped due to transfer issues?

To prevent something like that you need to inspect the time stamps: `image.raw_timestamp`. It is called raw as this is just a number. The meaning depends on the hardware used… For more in depth description on transfer monitoring look at post here:

[https://forum.commonvisionblox.com/t/getting-started-with-cvb-net/246/15?u=parsd](https://forum.commonvisionblox.com/t/getting-started-with-cvb-net/246/15)

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<div class="post-metadata">

**Author:** ![piotrM](https://avatars.discourse-cdn.com/v4/letter/p/d07c76/32.png) [@piotrM](https://forum.commonvisionblox.com/u/piotrM)\
**Post date:** [March 3, 2020, 10:37am UTC](https://forum.commonvisionblox.com/t/how-to-acquiring-only-the-latest-image-from-the-buffer/1061/3 "2020-03-03T10:37:47Z")

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Thanks a lot! Sorry for a late response. I will try this code out and let you know how it went.