Reading sent image over Uart

OpenMV Boards
1

Hi OpenMV People,

I was able to send and save an image from OpenMV to a Pycom board following OpenMV forums;

uart = UART(3, 115200, bits=8 , parity=None , timeout_char=2000)
img = img.compress(quality=10)
uart.write(img)

However, I have a hard time converting the saved image from Pycom flash memory to an image on my computer to check if it sent it correctly.
I found a base64 decode to image from this link: How to convert Byte Data to Image in Python (using Pillow library) - YouTube
Since Uart does not do base64 encoding mentioned in the video, I removed that part as follows and just tried to display it using imshow function; but it did not work;

import PIL.Image as Image
import io
from byte_array_fromOpenMV import byte_data
img = Image.open(byte_data)
img.show()

The start of OpenMV transmitted image looks like:

b’\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x01\x00\x00\x00\x00\x00\x00\xff\xfe\x00\x0c\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xdb\x00C\x00P7<F<2PFAFZUP_x\xc8\x82xnnx\xf5\xaf\xb9\x91\xc8\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xc0\x00\x0b\x08\x00<\x00P\x01\x01\x11\x00\xff\xc4\x00\x1f\x00\x00\x01\x05\x01\x01\x01\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\xff\xc4\x00\xb5\x10\x00\x02\x01\x03\x03\x02\x04\x03\x05\x05\x04\x04\x00\x00\x01}\x01\x02\x03\x00\x04\x11\x05\x12!1A\x06\x13Qa\x07"q\x142\x81\x91\xa1\x08#B\xb1\xc1\x15R\xd1\xf0$3br\x82\t\n\x16\x17\x18\x19\x1a%&'()*456789:CDEFGHIJSTUVWXYZcdefghijstuvwxyz\x83.…’

The Python Error in Computer;
UnicodeDecodeError: ‘utf-8’ codec can’t decode byte 0xff in position 0: invalid start byte

I am not sure what type the file transmitted is, it looks like it is a hex file, but I don’t know how to convert it back to an image!

Thank you in advance for your help!
MoZen

2

It’s a JPEG image, save it to file and open it.

1 Like
3

Thanks, yes eventually I realized it is JPEG.
I used ubinascii.b2a_base64(img.compress(quality=10)) to make it base64 encoding then decoded it using the mentioned code in the computer and got back the image.

4

Hi! I have question about data size. I want to send an image object through UART to another STM32, and then via COM port to PC (then in Qt process it into an image, like here.
In order to receive data from OpenMV by STM32 I need to know the length of message sent. Can it be known? Is it a constant value, like for example 32 bytes?
Thanks!
Also, If you have any suggestions on how my idea can be done easier, I’m open for it :slight_smile:

5

Use the RPC interface library please.

6

I would prefer not to, because I dont want to use RPC library on my STM32 in order to receive this data. I would just like to know the size of message. If its not constant value, or known value then okay. I will find a way through.

7

That’s fine. But, we’ve answered so many questions about basic python programming and how to write UART code that we wrote the library.

As such… please search the forums for previous answers on this for help support. Generally, syncing data between two devices is hard and you need to know what you are doing and how COMs work to get a good result. Our library makes that easy for you.